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Photo: Matt www.flickr.com/photos/cheaterfive/
1. Pectoralis Major
Latin, pectoralis, chest; major, large.
Along with pectoralis minor, it forms the anterior wall of the axilla.
Origin
Clavicular head: Medial half or two-thirds of front of clavicle. Sternocostal portion: Sternum and adjacent upper six costal cartilages.
Insertion
Upper shaft of humerus.
Action
Adducts and medially rotates the humerus.
Clavicular portion Flexes and medially rotates the shoulder joint, and horizontally adducts the humerus towards the opposite shoulder. Sternocostal portion: Obliquely adducts the humerus toward the opposite hip. The pectoralis major is one of the main climbing muscles, pulling the body up to the fixed arm.
Nerve
Nerve to upper fibres: Lateral pectoral nerve, C5, 6, 7.
Nerve to lower fibres: Lateral and medial pectoral nerves, 6, 7, 8, T1.
Basic functional movement
Clavicular portion: Brings arm forwards and across the body, as in applying deodorant to opposite armpit.
Sternal portion: Pulling down from above, such as a rope in bell ringing.
Sports that heavily utilise this muscle
Examples: Racket sports such as tennis. Golf. Baseball pitching. Gymnastics (rings and high bar). Judo. Wrestling.
Movements or injuries that may damage this muscle
Indian wrestling and other strength activities that force medial rotation and adduction can damage the insertion of this muscle.
Common problems when muscle is tight
Rounds the back and restricts expansion of chest, restricting lateral rotation and abduction of the shoulder.
Strengthening exercises
Bench press
Dumb-bell flyes
Vertical flyes ('pec deck' machine/ seated butterfly)
Pull-overs
Dips
Self stretches
Fix arm against a door frame. Step forward keeping your back lengthened, not arched. Raising or lowering arm will stretch different parts of the muscle.
2. Seratus anterior
Latin, serratus, notched; anterior, before.
The serratus anterior forms the medial wall of the axilla, along with the upper five ribs. It is a large muscle composed of a series of finger-like slips. The lower slips interdigitate with the origin of the external oblique.
Origin
Outer surfaces and superior borders of upper eight or nine ribs, and the fascia covering their intercostal spaces.
Insertion
Anterior (costal) surface of the medial border of scapula and inferior angle of scapula.
Action
Protracts scapula (pulls it forward on the ribs and holds it closely into the chest wall). Rotates scapula for abduction and flexion of arm.
Nerve
Long thoracic nerve, C5, 6, 7, 8.
Basic functional movement
PUshing or reaching forwards for something barely within reach.
Sports that heavily utilise this muscle
Examples: Boxing. Shot put.
Common problems when muscle is weak
'Winged scapula' (looking like an angel's wing), especially when holding a weight in front of the body. This is also a feature when the nerve to this muscle is damaged.
Strengthening exercises
Bench press (including inclined version)
Shoulder press
Press ups
Self stretch
In a seated position, hold seat of chair with one arm while turing in the opposite direction.
*Sorrel's note: This muscle is also known as the "super hero muscle" because it is always huge on super heros. The animators have the right idea, because one of the best ways to strengthen this muscle is by punching.
3. Rectus abdominus
Latin, rectum, straight; abdominis, belly/ stomach.
The rectus abdominis is divided into three or four bellies by tendinous muscles. These fibres converge centrally to form the linea alba. Situated anterior to the lower part of rectus abdominis is a frequently absent muscle called pyramidalis, which arises from the pubic crest and inserts into the linea alba. It tenses the linea alba, for reasons unknown. Associated with the six-pack muscles seen in conditioned athletes.
Origin
Pubic crest and symphysis (front of pubic bone).
Insertion
Xiphoid process (base of sternum). Fifth, sixth and seventh costal cartilages.
Action
Flexes lumbar spine. Depresses ribcage. Stabilizes the pelvis during walking.
Nerve
Ventral rami of thoracic nerves, T5-T12.
Basic functional movement
Example: Initiating getting out of a low chair.
Sports that heavily utilise this muscle
All sports.
Common problems when muscle is weak
Injury to lumbar spine, because abdominal muscle tone contributes to stability of lumbar spine.
Strengthening exercises
Sit-ups
Abdominal machine crunch (for upper fibres)
Reverse sit-up (for lower fibres_
Hanging leg raise
4. External (and internal) oblique
Latin, obliquus, diagonal, slanted.
The posterior fibres of the external oblique are usually overlapped by the latissimus dorsi, but in some cases there is a space between the two, known as the lumbar triangle, situated just above the iliac crest. The lumbar triangle is a weak point in the abdominal wall.
Origin
External oblique: Lower eight ribs.
Internal oblique: Iliac crest. Lateral two-thirds of inguinal ligament.
Thoracolumbar fascia (i.e. sheet of connective tissue in lower back).
Insertion
External oblique: Anterior half of iliac crest, and into an abdominal aponeurosis that terminates in the linea alba (a tendinous band extending downwards from the sternum).
Internal oblique: Bottom three or four ribs, and linea alba via aponeurosis.
Action
Compresses abdomen, helping to support the abdominal viscera against the pull of gravity. Contraction of one side alone bends the trunk laterally to that side and rotates in to the opposite side.
Nerve
External oblique: Ventral rami of thoracic nerves, T5-T12.
Internal oblique: Ventral rami of thoracic nerves, T7-T12, ilioinguinal and iliohypogastric nerves.
Basic functional movement
Example: Digging with a shovel, raking.
Sports that heavily utilise these muscles
External obliques: Examples: Gymnastics. Rowing. Rugby.
Internal obliques: Examples: Golf. Javelin. Pole vault.
Common problems when muscles are weak
Injury to lumbar spine, because abdominal muscle tone contributes to stability of lumbar spine.
Strengthening exercises
Twisting it-ups
Abdominal machine crunch (for upper fibers)
Hanging leg raise
Reverse trunk twist
Side bends
Self Stretches
Try to twist using trunk rather than shoulders or arms.
Perform this exercise slowly, thus avoiding the tendency to use momentum.
Avoid or take care if you have back problems; check with your health professional first.
5. Trapezius
Greek, trapezoides, table shaped.
The left and right trapezius, viewed as a whole, create a trapezium in shape, thus giving this muscle its name.
Origin
Base of skull (occipital bone). Spinous processes of seventh cervical (C7) and all thoracic vertebrae, (T1-T12).
Insertion
Lateral third of clavicle. Acromion process. Spine of scapula.
Action
Upper fibres: Pull the shoulder girdle up (elevation). Helps prevent depression of the shoulder girdle when a weight is carried on he shoulder or in the hand.
Middle fibres: Retract (adduct) scapula.
Lower fibres: Depress scapula, particularly against resistance, as when using the hands to get up from a chair.
Upper and lower fibres together: Rotate scapula, as in elevating the arm above the head.
Nerve
Accessory X1 nerve. Ventral ramus of cervical nerves, C2, 3, 4.
Basic functional movement
Example (upper and lower fibres working together): Painting a ceiling.
Sports that heavily utilise this muscle
Examples: Shot put. Boxing. Seated rowing.
Common problems when muscle is chronically tight/ shortened
Upper fibres: Neck pain or stiffness, headaches.
Strengthening exercises
Shoulder press (upper fibres)
Dips (middle/lower fibres)
Chin-ups (middle/lower fibres)
Lateral dumb-bell raises
Stretches
Turn head to right and tuck chin in. Pull left shoulder down. Pull head and left shoulder apart from each other.
6. Omohyoid
7. Sternocleidomastoideus
Greek, sternon, sternum; kleidos, key, clavicle; mastoid, breast-shaped, mastoid process.
This muscle is a long strap muscle with two heads. It is sometimes injured at birth, and may be partly replaced by fibrous tissue that contracts to produce a torticollis (wry neck).
Origin
Sternal head: Anterior surface of upper sternum. Clavicular head: Medial third of clavicle.
Insertion
Mastoid process of temporal bone (bony prominence just behind the ear).
Action
Contraction of both sides together: Flexes neck (draws head forward). Raises sternum, and consequently the ribs, during deep inhalation. Contraction of one side: Tilts the head towards the same side. Rotates head to face the opposite side (and also upward as it does so).
Nerve
Accessory X1 nerve; with sensory supply for proprioception from cervical nerves C2 and C3.
Basic functional movement
Examples: Turning head to look over your shoulder. Raising head from pillow.
Sports that heavily utilise this muscle
Examples: Swimming. Rugby scrummage. American football.
Movements or injuries that may damage this muscle
Extreme whiplash movements.
Common problems when muscle is chronically tight/ shortened
Headache and neck pain.
Strengthening exercise
Sit-ups
Self stretch
Turn head to right. Repeat on opposite side.
8. Subclavius
9. Pectoralis minor
Latin, pectoralis, chest; minor, small.
Pectoralis minor is a flat triangular muscle lying posterior to, and concealed by, pectoralis major. Along with pectoralis major, it forms the anterior wall of the axilla.
Origin
Outer surfaces of third, fourth and fifth ribs and fascia of the corresponding intercostal spaces.
Insertion
Corocoid process of scapula.
Action
Draws scapula forward and downward. Raises ribs during forced inspiration (i.e. it is an accessory muscle of inspiration, if the scapula is stabilized by the rhomboids and trapezius).
Nerve
Medial pectoral nerve with fibres from a communicating branch of the lateral pectoral nerve, C(6), 7, 8 T1.
Basic functional movement
Example: Pushing on arms of chair to stand up.
Sports that heavily utilise this muscle
Racket sports, e.g. tennis, badminton. Baseball pitching. Sprinting.
Common problems when muscle is chronically tight/ shortened
Restricts expansion of chest.
Strengthening exercises
Bench press
Dumb-bell flyes
Pull-overs
Self stretches
Fix arm against a door frame. Step forward keeping your back lengthened, not arched. Raising or lowering arm will stretch different parts of the muscle.
10. Internal intercostal & 11. External intercostal
Latin, inter, between; costal, rib.
The lower external intercostal muscles may blend with the fibres of external oblique, which overlap them, thus effectively forming one continuous sheet of muscle, with the external intercostal fibres seemingly stranded between the ribs. There are 11 external intercostals on each side of the ribcage.
Internal intercostal fibres lie deep to, and run obliquely across, the external intercostals. There are 11 internal intercostals on each side of the ribcage.
Origin
External intercostals: Lower border of a rib.
Internal intercostals: Upper border of a rib and costal cartilage.
Insertion
External intercostals: Upper border of rib below (fribres run obliquely forwards and downwards).
Internal intercostals: Lower border of rib above (fibres run obliquely forwards and upwards towards the costal cartilage).
Action
Muscles contract to stabilize the ribcage during various movements of the trunk. Prevents the intercostal space from bulging out or sucking in during respiration.
Nerve
The corresponding intercostal nerves.
Sports that heavily utilise these muscles
All very active sports.
Common problems when muscles are chronically tight/ shortened
Kyphosis (rounded back) and depressed chest.
Strengthening exercise
Twisting sit-ups
Self stretch
Avoid or take care if you have back problems; check with your health professional first.
12. Internal (and external) oblique
Latin, obliquus, diagonal, slanted.
The posterior fibres of the external oblique are usually overlapped by the latissimus dorsi, but in some cases there is a space between the two, known as the lumbar triangle, situated just above the iliac crest. The lumbar triangle is a weak point in the abdominal wall.
Origin
External oblique: Lower eight ribs.
Internal oblique: Iliac crest. Lateral two-thirds of inguinal ligament.
Thoracolumbar fascia (i.e. sheet of connective tissue in lower back).
Insertion
External oblique: Anterior half of iliac crest, and into an abdominal aponeurosis that terminates in the linea alba (a tendinous band extending downwards from the sternum).
Internal oblique: Bottom three or four ribs, and linea alba via aponeurosis.
Action
Compresses abdomen, helping to support the abdominal viscera against the pull of gravity. Contraction of one side alone bends the trunk laterally to that side and rotates in to the opposite side.
Nerve
External oblique: Ventral rami of thoracic nerves, T5-T12.
Internal oblique: Ventral rami of thoracic neres, T7-T12, ilioinguinal and iliohypogastric nerves.
Basic functional movement
Example: Digging with a shovel, raking.
Sports that heavily utilise these muscles
External obliques: Examples: Gymnastics. Rowing. Rugby.
Internal obliques: Examples: Golf. Javelin. Pole vault.
Common problems when muscles are weak
Injury to lumbar spine, because abdominal muscle tone contributes to stability of lumbar spine.
Strengthening exercises
Twisting it-ups
Abdominal machine crunch (for upper fibers)
Hanging leg raise
Reverse trunk twist
Side bends
Self Stretches
Try to twist using trunk rather than shoulders or arms.
Perform this exercise slowly, thus avoiding the tendency to use momentum.
Avoid or take care if you have back problems; check with your health professional first.
13. Linea alba
14. Bicep brachii
Latin, biceps, two-headed muscle; brahii, of the arm.
Biceps brachii operates over three joints. It has two tendinous heads at its origin and two tendinous insertions. Occasionally it has a third head, originating at the insertion of coracobrachialis. The short head forms part of the lateral wall of the axilla, along with coracograchialis and the humerus.
Origin
Short head: Tip of coracoid process of scapula.
Long head: Supraglenoid tubercle of scapula (area just above socket of shoulder joint).
Insertion
Radial tuberosity (on medial aspect of upper part of shaft of radius). Deep fascia (connective tissue) on medial aspect of forearm.
Action
Flexes elbow joint. Supinates forearm. (It has been described as the muscle that puts in the corkscrew and pulls out the cork). Weakly flexes arm at the shoulder joint.
Nerve
Musculocutaneous nerve, C5, 6.
Basic functional movement
Examples: Picking up an object. Bringing food to mouth.
Sports that heavily utilise this muscle
Examples: Boxing. Climbing. Canoeing. Rowing.
Movements or injuries that may damage this muscle
Lifting heavy objects too suddenly.
Common problems when muscle is chronically tight/ shortened
Flexion deformity of elbow (elbow cannot be fully straightened).
Strengthening exercises
Biceps curl
Chin-ups
Lat. pull downs
External (and internal) oblique
Latin, obliquus, diagonal, slanted.
The posterior fibres of the external oblique are usually overlapped by the latissimus dorsi, but in some cases there is a space between the two, known as the lumbar triangle, situated just above the iliac crest. The lumbar triangle is a weak point in the abdominal wall.
Origin
External oblique: Lower eight ribs.
Internal oblique: Iliac crest. Lateral two-thirds of inguinal ligament.
Thoracolumbar fascia (i.e. sheet of connective tissue in lower back).
Insertion
External oblique: Anterior half of iliac crest, and into an abdominal aponeurosis that terminates in the linea alba (a tendinous band extending downwards from the sternum).
Internal oblique: Bottom three or four ribs, and linea alba via aponeurosis.
Action
Compresses abdomen, helping to support the abdominal viscera against the pull of gravity. Contraction of one side alone bends the trunk laterally to that side and rotates in to the opposite side.
Nerve
External oblique: Ventral rami of thoracic nerves, T5-T12.
Internal oblique: Ventral rami of thoracic neres, T7-T12, ilioinguinal and iliohypogastric nerves.
Basic functional movement
Example: Digging with a shovel, raking.
Sports that heavily utilise these muscles
External obliques: Examples: Gymnastics. Rowing. Rugby.
Internal obliques: Examples: Golf. Javelin. Pole vault.
Common problems when muscles are weak
Injury to lumbar spine, because abdominal muscle tone contributes to stability of lumbar spine.
Strengthening exercises
Twisting it-ups
Abdominal machine crunch (for upper fibers)
Hanging leg raise
Reverse trunk twist
Side bends
Self Stretches
Try to twist using trunk rather than shoulders or arms.
Perform this exercise slowly, thus avoiding the tendency to use momentum.
Avoid or take care if you have back problems; check with your health professional first.
15. Triceps
Latin, triceps, three-headed muscle; brachii, of the arm.
The triceps originates from three heads and is the only muscle on the back of the arm.
Origin
Long head: Infraglenoid tubercle of the scapula (area just below socket of shoulder joint).
Lateral head: Upper half of posterior surface of shaft of humerus.
Medial head: Lower half of posterior surface of shaft of humerus.
Insertion
Olecranon process of the ulna (i.e. upper posterior area of ulna, near the point of the elbows).
Action
Extends (straightens) elbow joint. Long head can adduct the humerus and extend it from the flexed position. Stabilizes shoulder joint.
Nerve
Radial nerve, C6, 7, 8, T1.
Basic functional movement
Examples: Throwing objects. Pushing a door shut.
Sports that heavily utilise this muscle
Examples: Basketball or netball (shooting). Shot put. baseball (pitcher). Volleyball.
Movements or injuries that may damage this muscle
Throwing with excessive force.
Problems when muscle is chronically tight/ shortened
Extension deformity of elbow (elbow cannot be fully flexed); although not very common.
Strengthening exercises
Bench press
Push-ups
Dips
Triceps kick-back
Self Stretches
Keep your head up and elbow as far back as it comfortable, without hollowing your lower back.
Pull your hands towards each other. Most effective when the raised elbow is against the wall.
16. Extensor digitorum
17. Extensor digiti minimi (finger extensors)
Latin, extensor, to extend; digit, finger.
Origin
Common extensor tendon from lateral epicondyle of humerus (i.e. lower lateral end of humerus).
Insertion
Dorsal surfaces of all the phalanges of the four fingers.
Action
Extends the fingers. Assists abduction (divergence) of fingers away from the middle finger.
Nerve
Deep radial (posterior interosseous) nerve, 6, 7, 8.
Basic functional movement
Example: Letting go of objects held in the hand.
Movements or injuries that may damage this muscle
Overflexing the wrist resulting from falling onto the hand.
Common problems when muscle is chronically tight/ shortened/ overused
Tennis elbow (overuse tendonitis of common origin on lateral epicondyle of humerus).
Self stretch
Use one hand to gently lever wrist and fingers into extension.
18. Extensor carpi ulnaris (wrist extensors)
Latin, extensor, to extend.
Includes extensor carpi radialis longus and brevis, and extensor carpi ulnaris.
Origin
Common extensor tendon from lateral epicondyle of humerus (i.e. lower lateral end of humerus).
Insertion
Dorsal surface of metacarpal bones.
Action
Extends the wrist (extensor carpi radialis longus and brevis also abduct the wrist; extensor carpi ulnaris also adducts the wrist).
Nerve
Radialis longus and brevis: Radial nerve, C5, 6, 7, 8.
Extensor carpi ulnaris: Deep radial (posterior interosseous) nerve, C6, 7, 8.
Basic functional movement
Examples: Kneading dough. Typing. Cleaning windows.
Sports that heavily utilise these muscles
Examples: Back hand badminton. Golf. Motorcycle sports (throttle control).
Movements or injuries that may damage these muscles
Overflexing the wrist resulting from falling onto the hand.
Common problems when muscles are chronically tight / shortened/ overused
Tennis elbow (overuse tendonitis of common origin on lateral epicondyle of humerus).
Strengthening exercises
Wrist roller (palm down)
Reverse wrist curl
Most dumb-bell exercises
Self stretches
Use lower hand to gently lever the other wrist into flexion.
19. Flexor carpi ulnaris
Latin, flex, to bend.
Includes: flexor carpi radialis, palmaris longus, flexor carpi ulnaris.
Origin
Common flexor origin on the anterior aspect of the medial epicondyle of humerus (i.e. lower medial end of humerus).
Insertion
Carpals, metacarpals and phalanges.
Action
Flex the wrist (flexor carpi radialis also abducts the wrist; flexor carpi ulnaris also adducts the wrist).
Nerve
Flexor carpi radialis: Median nerve, C6, 7, 8.
Palmaris longus: Median nerve, C(6), 7, 8, T1.
Flexor carpi ulnaris: Ulnar nerve, C7, 8, T1.
Basic functional movement
Examples: Pulling rope in towards you. Wielding an axe or hammer.
Sports that heavily utilise these muscles
Examples: Sailing. Water skiing. Golf. Baseball. Cricket. Volleyball.
Movements or injuries that may damage these muscles
Overextending the wrist resulting from breaking a fall with the hand.
Common problems when muscles are chronically tight/ shortened/ overused
Golfer's elbow (overuse tendonitis of common flexor origin), carpal tunnel syndrome.
Strengthening exercises
Biceps curl
Wrist rolling (palm up)
Wrist curl
Self stretch
Use one hand to gently lever the other wrist into extension.
20. Anconeus
"Aranha em Escala de Cinza", 03 fotos. Usei a Canon 60D, objetivas 70x300mm e a 70x200mm L com extensor tele 2x.
"Gray Scale Spider", 03 photos. I used the Canon 60D, 70x300mm lenses and 70x200mm L with 2x tele extender.
Todos os direitos reservados para Vivaldo Armelin Júnior
Por insignificante que parezca, cada criatura en la tierra tiene su papel y aunque lo desconozcamos realiza una función en el ecosistema, esto es una muestra de ese pequeño mundo dificil de percibir a simple vista.
Uso un objetivo 35-105mm f/3,5 - 4,5 análogo con extensores para lograr este aumento, todo es manual !!
William Optics Zenithstar 61
ZWO ASI120MM
Extensor Orión 1.25
Tripie
700 frames
Frames usados 500
Df: 360
F: 6
Captura: Firecapture
Revelado: Autostakkert + Fitsworks + Lr
Guillermo Cervantes Mosqueda
Observatorio Astronómico Altaïr
Poncitlán Jalisco México
Link para o programa de aumento peniano grátis - machoalphaoficial.com.br/0/aumento-peniano-gratis
Como dito no vídeo para você conseguir aumentar o tamanho do seu pênis é simples mas não é fácil, por que exige um certo empenho para praticar os exercícios de aumento peniano e conseguir finalmente um resultado consistente.
Então para quem tem dúvida se o aumento peniano é verdade ou não, pode acreditar é a mais pura verdade e vou explicar o motivo. O pênis é um músculo e assim como qualquer outro músculo quando estimulado do jeito correto ele sofre uma alteração ficando maior do que era antes e com o tempo isso vai começando a ficar visível. Isso acontece da mesma forma, quando você quer aumentar o tamanho do pênis basta fazer os exercícios corretos para isso e conseguir chegar no resultado almejado.
Nós estamos dando um material de aumento peniano gratuitamente para você poder começar a fazer os exercícios hoje mesmo se possível. Porem, também temos um programa completo com 26 exercícios de aumento peniano que além de deixar o seu pênis maior vai aumentar sua grossura ao mesmo tempo.
Esses exercícios além de aumentar o tamanho do seu brinquedo ajuda em outras coisas como melhorar o seu desempenho sexual, permanecer por mais tempo no sexo, vai te dar um controle total sobre a ejaculação eliminando de uma vez por todas a ejaculação precoce, você vai ter um ereção muito mais rígida e um tempo muito mais curto entre cada ereção.
Mas não estou falando para você comprar nada, por isso estou dando de graça parte dos exercícios do aumento peniano em vídeo-aulas para você aproveitar ao máximo e poder ter um pênis maior, e assim melhorando suas relações sexuais.
Link para o programa de aumento peniano grátis - machoalphaoficial.com.br/0/aumento-peniano-gratis
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Llevamos unos días de buen tiempo, y esto hace que los bichos se animen a salir. Hoy uno de estos simpáticos bichitos se ha animado a hacerme una visita. Lo que yo he interpretado como una oportunidad magnífica para montar en mi 17-70mm el anillo extensor - 20 mm -que un amigo me ha prestado (gracias EwarArt).
La foto esta tal cual sin tocar ningún parámetro, tan solo he borrado algún pelo y polvo que había sobre la mesa y una sombra más oscura en la parte superior (por el flash).
Acabo de devolver al visitante a la calle sano y salvo ;-)
Entre l'interior i l'exterior, algunes plantes, hi coloquen les seve defenses.
Aquesta és una fulla, bé un fragment , ja que tota la fulla ho vaig creure com massa gran.
La veritat és que fan un bon respecte aquestes punxes. No vaig noler possar-hi el dit.
Algunes vegades tens ganes que entre el teu exterior i allò que sents a dins hi haguçessin punxes com les d'aq8ueste plante, després quan perceb que has pogut fet mal et sap greu i pensa que per aquesta planta està molt bé, però per un ésse humà potser no cal.
Una molt bona setmana a tothom
Modelo: Caro contreras
Strobist info: SB800 en 45º con gel rojo vía CLS, SB800 con gel 1/2 CTS a la izquierda y arriba atravez de un paragua traslucido con cable extensor TTL comandando al flash de atrás.
Spiders (order Araneae) are air-breathing arthropods that have eight legs and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of November 2015, at least 45,700 spider species, and 114 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.
Anatomically, spiders differ from other arthropods in that the usual body segments are fused into two tagmata, the cephalothorax and abdomen, and joined by a small, cylindrical pedicel. Unlike insects, spiders do not have antennae. In all except the most primitive group, the Mesothelae, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.
Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of glands. Spider webs vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-web spiders. Spider-like arachnids with silk-producing spigots appeared in the Devonian period about 386 million years ago, but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years ago, and are very similar to the most primitive surviving suborder, the Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appeared in the Triassic period, before 200 million years ago.
A herbivorous species, Bagheera kiplingi, was described in 2008, but all other known species are predators, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lassoing it with sticky bolas, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the genus Portia show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, and they liquefy their food by flooding it with digestive enzymes and grinding it with the bases of their pedipalps, as they do not have true jaws.
Male spiders identify themselves by a variety of complex courtship rituals to avoid being eaten by the females. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the widow spiders, to co-operative hunting and food-sharing. Although most spiders live for at most two years, tarantulas and other mygalomorph spiders can live up to 25 years in captivity.
While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticides. Spider silk provides a combination of lightness, strength and elasticity that is superior to that of synthetic materials, and spider silk genes have been inserted into mammals and plants to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and mythology symbolizing various combinations of patience, cruelty and creative powers. An abnormal fear of spiders is called arachnophobia.
DESCRIPTION
BODY PLAN
Spiders are chelicerates and therefore arthropods. As arthropods they have: segmented bodies with jointed limbs, all covered in a cuticle made of chitin and proteins; heads that are composed of several segments that fuse during the development of the embryo.[7] Being chelicerates, their bodies consist of two tagmata, sets of segments that serve similar functions: the foremost one, called the cephalothorax or prosoma, is a complete fusion of the segments that in an insect would form two separate tagmata, the head and thorax; the rear tagma is called the abdomen or opisthosoma. In spiders, the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel. The pattern of segment fusion that forms chelicerates' heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the antennae typical of most arthropods. In fact, chelicerates' only appendages ahead of the mouth are a pair of chelicerae, and they lack anything that would function directly as "jaws". The first appendages behind the mouth are called pedipalps, and serve different functions within different groups of chelicerates.
Spiders and scorpions are members of one chelicerate group, the arachnids. Scorpions' chelicerae have three sections and are used in feeding. Spiders' chelicerae have two sections and terminate in fangs that are generally venomous, and fold away behind the upper sections while not in use. The upper sections generally have thick "beards" that filter solid lumps out of their food, as spiders can take only liquid food. Scorpions' pedipalps generally form large claws for capturing prey, while those of spiders are fairly small appendages whose bases also act as an extension of the mouth; in addition, those of male spiders have enlarged last sections used for sperm transfer.
In spiders, the cephalothorax and abdomen are joined by a small, cylindrical pedicel, which enables the abdomen to move independently when producing silk. The upper surface of the cephalothorax is covered by a single, convex carapace, while the underside is covered by two rather flat plates. The abdomen is soft and egg-shaped. It shows no sign of segmentation, except that the primitive Mesothelae, whose living members are the Liphistiidae, have segmented plates on the upper surface.
Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas round the reproductive and excretory systems. Its place is largely taken by a hemocoel, a cavity that runs most of the length of the body and through which blood flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end. However, in spiders, it occupies only the upper part of the abdomen, and blood is discharged into the hemocoel by one artery that opens at the rear end of the abdomen and by branching arteries that pass through the pedicle and open into several parts of the cephalothorax. Hence spiders have open circulatory systems. The blood of many spiders that have book lungs contains the respiratory pigment hemocyanin to make oxygen transport more efficient.
Spiders have developed several different respiratory anatomies, based on book lungs, a tracheal system, or both. Mygalomorph and Mesothelae spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen. This is also the case for some basal araneomorph spiders, like the family Hypochilidae, but the remaining members of this group have just the anterior pair of book lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs. The trachea system has most likely evolved in small ancestors to help resist desiccation. The trachea were originally connected to the surroundings through a pair of openings called spiracles, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and moved backwards close to the spinnerets. Spiders that have tracheae generally have higher metabolic rates and better water conservation. Spiders are ectotherms, so environmental temperatures affect their activity.
FEEDING, DIGESTION AND EXCRETION
Uniquely among chelicerates, the final sections of spiders' chelicerae are fangs, and the great majority of spiders can use them to inject venom into prey from venom glands in the roots of the chelicerae. The family Uloboridae has lost its venom glands, and kills its prey with silk instead. Like most arachnids, including scorpions, spiders have a narrow gut that can only cope with liquid food and spiders have two sets of filters to keep solids out. They use one of two different systems of external digestion. Some pump digestive enzymes from the midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the pedipalps, while flooding it with enzymes; in these species, the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing.
The stomach in the cephalothorax acts as a pump that sends the food deeper into the digestive system. The mid gut bears many digestive ceca, compartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax.
Most spiders convert nitrogenous waste products into uric acid, which can be excreted as a dry material. Malphigian tubules ("little tubes") extract these wastes from the blood in the hemocoel and dump them into the cloacal chamber, from which they are expelled through the anus. Production of uric acid and its removal via Malphigian tubules are a water-conserving feature that has evolved independently in several arthropod lineages that can live far away from water,[14] for example the tubules of insects and arachnids develop from completely different parts of the embryo. However, a few primitive spiders, the sub-order Mesothelae and infra-order Mygalomorphae, retain the ancestral arthropod nephridia ("little kidneys"), which use large amounts of water to excrete nitrogenous waste products as ammonia.
CENTRAL NERVOS SYSTEM
The basic arthropod central nervous system consists of a pair of nerve cords running below the gut, with paired ganglia as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the esophagus is encircled by this conglomeration of ganglia. Except for the primitive Mesothelae, of which the Liphistiidae are the sole surviving family, spiders have the much more centralized nervous system that is typical of arachnids: all the ganglia of all segments behind the esophagus are fused, so that the cephalothorax is largely filled with nervous tissue and there are no ganglia in the abdomen; in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused.
Despite the relatively small central nervous system, some spiders (like Portia) exhibit complex behaviour, including the ability to use a trial-and-error approach.
SENSE ORGANS
EYES
Most spiders have four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropods are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However, the main eyes at the front of spiders' heads are pigment-cup ocelli that are capable of forming images. The other eyes are thought to be derived from the compound eyes of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the main eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidum, and wolf spiders can be spotted by torch light reflected from the tapeta. On the other hand, jumping spiders' secondary eyes have no tapeta. Some jumping spiders' visual acuity exceeds by a factor of ten that of dragonflies, which have by far the best vision among insects; in fact the human eye is only about five times sharper than a jumping spider's. They achieve this by a telephoto-like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.
There are spiders with a reduced number of eyes, of these those with six-eyes are the most numerous and are missing a pair of eyes on the anterior median line, others species have four-eyes and some just two. Cave dwelling species have no eyes, or possess vestigial eyes incapable of sight.
OTHER SENSES
As with other arthropods, spiders' cuticles would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact, spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called setae, respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste and smell, often by means of setae. Pedipalps carry a large number of such setae sensitive to contact chemicals and air-borne smells, such as female pheromones. Spiders also have in the joints of their limbs slit sensillae that detect forces and vibrations. In web-building spiders, all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively.
Like most arthropods, spiders lack balance and acceleration sensors and rely on their eyes to tell them which way is up. Arthropods' proprioceptors, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. On the other hand, little is known about what other internal sensors spiders or other arthropods may have.
LOCOMOTION
Each of the eight legs of a spider consists of seven distinct parts. The part closest to and attaching the leg to the cephalothorax is the coxa; the next segment is the short trochanter that works as a hinge for the following long segment, the femur; next is the spider's knee, the patella, which acts as the hinge for the tibia; the metatarsus is next, and it connects the tibia to the tarsus (which may be thought of as a foot of sorts); the tarsus ends in a claw made up of either two or three points, depending on the family to which the spider belongs. Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. The only extensor muscles in spider legs are located in the three hip joints (bordering the coxa and the trochanter). As a result, a spider with a punctured cephalothorax cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs. Although larger spiders use hydraulics to straighten their legs, unlike smaller jumping spiders they depend on their flexor muscles to generate the propulsive force for their jumps.
Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine hairs between the paired claws at the tips of their legs. These tufts, known as scopulae, consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. Spiders, like most other arachnids, keep at least four legs on the surface while walking or running.
SILK PRODUCTION
The abdomen has no appendages except those that have been modified to form one to four (usually three) pairs of short, movable spinnerets, which emit silk. Each spinneret has many spigots, each of which is connected to one silk gland. There are at least six types of silk gland, each producing a different type of silk.
Silk is mainly composed of a protein very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein. It is similar in tensile strength to nylon and biological materials such as chitin, collagen and cellulose, but is much more elastic. In other words, it can stretch much further before breaking or losing shape.
Some spiders have a cribellum, a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum, a comb-like set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However, most modern groups of spiders have lost the cribellum.
Tarantulas also have silk glands in their feet.
Even species that do not build webs to catch prey use silk in several ways: as wrappers for sperm and for fertilized eggs; as a "safety rope"; for nest-building; and as "parachutes" by the young of some species.
REPRODUCTION AND LIFE CYCLE
Spiders reproduce sexually and fertilization is internal but indirect, in other words the sperm is not inserted into the female's body by the male's genitals but by an intermediate stage. Unlike many land-living arthropods, male spiders do not produce ready-made spermatophores (packages of sperm), but spin small sperm webs on to which they ejaculate and then transfer the sperm to special syringe-like structures, palpal bulbs or palpal organs, borne on the tips of the pedipalps of mature males. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or "safety ropes", the male can identify the species and sex of these objects by "smell".
Spiders generally use elaborate courtship rituals to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In web-weaving species, precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female's body are important in many spiders that hunt actively, and may "hypnotize" the female. Gestures and dances by the male are important for jumping spiders, which have excellent eyesight. If courtship is successful, the male injects his sperm from the palpal bulbs into the female's genital opening, known as the epigyne, on the underside of her abdomen. Female's reproductive tracts vary from simple tubes to systems that include seminal receptacles in which females store sperm and release it when they are ready.
Males of the genus Tidarren amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of male's body mass in this species, and detaching one of the two improves mobility. In the Yemeni species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime, the female feeds on the palpless male. In over 60% of cases, the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female's genital opening; in fact, the males co-operate by trying to impale themselves on the females' fangs. Observation shows that most male redbacks never get an opportunity to mate, and the "lucky" ones increase the likely number of offspring by ensuring that the females are well-fed. However, males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates' webs.
Females lay up to 3,000 eggs in one or more silk egg sacs, which maintain a fairly constant humidity level. In some species, the females die afterwards, but females of other species protect the sacs by attaching them to their webs, hiding them in nests, carrying them in the chelicerae or attaching them to the spinnerets and dragging them along.
Baby spiders pass all their larval stages inside the egg and hatch as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a wolf spider's brood cling to rough bristles on the mother's back, and females of some species respond to the "begging" behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitate food.
Like other arthropods, spiders have to molt to grow as their cuticle ("skin") cannot stretch. In some species males mate with newly molted females, which are too weak to be dangerous to the males. Most spiders live for only one to two years, although some tarantulas can live in captivity for over 20 years.
SIZE
Spiders occur in a large range of sizes. The smallest, Patu digua from Colombia, are less than 0.37 mm in body length. The largest and heaviest spiders occur among tarantulas, which can have body lengths up to 90 mm and leg spans up to 250 mm.
ECOLOGY AND BEHAVIOR
NON-PREDATORY FEEDING
Although spiders are generally regarded as predatory, the jumping spider Bagheera kiplingi gets over 90% of its food from fairly solid plant material produced by acacias as part of a mutually beneficial relationship with a species of ant.
Juveniles of some spiders in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae feed on plant nectar. Laboratory studies show that they do so deliberately and over extended periods, and periodically clean themselves while feeding. These spiders also prefer sugar solutions to plain water, which indicates that they are seeking nutrients. Since many spiders are nocturnal, the extent of nectar consumption by spiders may have been underestimated. Nectar contains amino acids, lipids, vitamins and minerals in addition to sugars, and studies have shown that other spider species live longer when nectar is available. Feeding on nectar avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes.
Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages.
METHODS OF CAPTURING PREY
The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations.
Females of the water spider Argyroneta aquatica build underwater "diving bell" webs that they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling.
Net-casting spiders weave only small webs, but then manipulate them to trap prey. Those of the genus Hyptiotes and the family Theridiosomatidae stretch their webs and then release them when prey strike them, but do not actively move their webs. Those of the family Deinopidae weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs' area by a factor of up to ten. Experiments have shown that Deinopis spinosus has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of Deinopis subrufa appears to live mainly on tipulid flies that they catch with the backwards strike.
Mature female bolas spiders of the genus Mastophora build "webs" that consist of only a single "trapeze line", which they patrol. They also construct a bolas made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromones of moths, and then swing the bolas at the moths. Although they miss on about 50% of strikes, they catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas. Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract moth flies, and catch them with their front pairs of legs.
The primitive Liphistiidae, the "trapdoor spiders" of the family Ctenizidae and many tarantulas are ambush predators that lurk in burrows, often closed by trapdoors and often surrounded by networks of silk threads that alert these spiders to the presence of prey. Other ambush predators do without such aids, including many crab spiders, and a few species that prey on bees, which see ultraviolet, can adjust their ultraviolet reflectance to match the flowers in which they are lurking. Wolf spiders, jumping spiders, fishing spiders and some crab spiders capture prey by chasing it, and rely mainly on vision to locate prey.Some jumping spiders of the genus Portia hunt other spiders in ways that seem intelligent, outflanking their victims or luring them from their webs. Laboratory studies show that Portia's instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species. However, they seem to be relatively slow "thinkers", which is not surprising, as their brains are vastly smaller than those of mammalian predators.
Ant-mimicking spiders face several challenges: they generally develop slimmer abdomens and false "waists" in the cephalothorax to mimic the three distinct regions (tagmata) of an ant's body; they wave the first pair of legs in front of their heads to mimic antennae, which spiders lack, and to conceal the fact that they have eight legs rather than six; they develop large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective hairs to resemble the shiny bodies of ants. In some spider species, males and females mimic different ant species, as female spiders are usually much larger than males. Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant; for example, many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus Synemosyna walk on the outer edges of leaves in the same way as Pseudomyrmex. Ant-mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However, several ant-mimicking spiders prey either on ants or on the ants' "livestock", such as aphids. When at rest, the ant-mimicking crab spider Amyciaea does not closely resemble Oecophylla, but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill, some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.
DEFENSE
There is strong evidence that spiders' coloration is camouflage that helps them to evade their major predators, birds and parasitic wasps, both of which have good color vision. Many spider species are colored so as to merge with their most common backgrounds, and some have disruptive coloration, stripes and blotches that break up their outlines. In a few species, such as the Hawaiian happy-face spider, Theridion grallator, several coloration schemes are present in a ratio that appears to remain constant, and this may make it more difficult for predators to recognize the species. Most spiders are insufficiently dangerous or unpleasant-tasting for warning coloration to offer much benefit. However, a few species with powerful venoms, large jaws or irritant hairs have patches of warning colors, and some actively display these colors when threatened.
Many of the family Theraphosidae, which includes tarantulas and baboon spiders, have urticating hairs on their abdomens and use their legs to flick them at attackers. These hairs are fine setae (bristles) with fragile bases and a row of barbs on the tip. The barbs cause intense irritation but there is no evidence that they carry any kind of venom. A few defend themselves against wasps by including networks of very robust threads in their webs, giving the spider time to flee while the wasps are struggling with the obstacles. The golden wheeling spider, Carparachne aureoflava, of the Namibian desert escapes parasitic wasps by flipping onto its side and cartwheeling down sand dunes.
SOZIAL SPIDERS
A few spider species that build webs live together in large colonies and show social behavior, although not as complex as in social insects. Anelosimus eximius (in the family Theridiidae) can form colonies of up to 50,000 individuals. The genus Anelosimus has a strong tendency towards sociality: all known American species are social, and species in Madagascar are at least somewhat social. Members of other species in the same family but several different genera have independently developed social behavior. For example, although Theridion nigroannulatum belongs to a genus with no other social species, T. nigroannulatum build colonies that may contain several thousand individuals that co-operate in prey capture and share food. Other communal spiders include several Philoponella species (family Uloboridae), Agelena consociata (family Agelenidae) and Mallos gregalis (family Dictynidae). Social predatory spiders need to defend their prey against kleptoparasites ("thieves"), and larger colonies are more successful in this. The herbivorous spider Bagheera kiplingi lives in small colonies which help to protect eggs and spiderlings. Even widow spiders (genus Latrodectus), which are notoriously cannibalistic, have formed small colonies in captivity, sharing webs and feeding together.
WEB TYPES
There is no consistent relationship between the classification of spiders and the types of web they build: species in the same genus may build very similar or significantly different webs. Nor is there much correspondence between spiders' classification and the chemical composition of their silks. Convergent evolution in web construction, in other words use of similar techniques by remotely related species, is rampant. Orb web designs and the spinning behaviors that produce them are the best understood. The basic radial-then-spiral sequence visible in orb webs and the sense of direction required to build them may have been inherited from the common ancestors of most spider groups. However, the majority of spiders build non-orb webs. It used to be thought that the sticky orb web was an evolutionary innovation resulting in the diversification of the Orbiculariae. Now, however, it appears that non-orb spiders are a sub-group that evolved from orb-web spiders, and non-orb spiders have over 40% more species and are four times as abundant as orb-web spiders. Their greater success may be because sphecid wasps, which are often the dominant predators of spiders, much prefer to attack spiders that have flat webs.
ORB WEBS
About half the potential prey that hit orb webs escape. A web has to perform three functions: intercepting the prey (intersection), absorbing its momentum without breaking (stopping), and trapping the prey by entangling it or sticking to it (retention). No single design is best for all prey. For example: wider spacing of lines will increase the web's area and hence its ability to intercept prey, but reduce its stopping power and retention; closer spacing, larger sticky droplets and thicker lines would improve retention, but would make it easier for potential prey to see and avoid the web, at least during the day. However, there are no consistent differences between orb webs built for use during the day and those built for use at night. In fact, there is no simple relationship between orb web design features and the prey they capture, as each orb-weaving species takes a wide range of prey.
The hubs of orb webs, where the spiders lurk, are usually above the center, as the spiders can move downwards faster than upwards. If there is an obvious direction in which the spider can retreat to avoid its own predators, the hub is usually offset towards that direction.
Horizontal orb webs are fairly common, despite being less effective at intercepting and retaining prey and more vulnerable to damage by rain and falling debris. Various researchers have suggested that horizontal webs offer compensating advantages, such as reduced vulnerability to wind damage; reduced visibility to prey flying upwards, because of the back-lighting from the sky; enabling oscillations to catch insects in slow horizontal flight. However, there is no single explanation for the common use of horizontal orb webs.
Spiders often attach highly visible silk bands, called decorations or stabilimenta, to their webs. Field research suggests that webs with more decorative bands captured more prey per hour. However, a laboratory study showed that spiders reduce the building of these decorations if they sense the presence of predators.
In 1973, Skylab 3 took two orb-web spiders into space to test their web-spinning capabilities in zero gravity. At first, both produced rather sloppy webs, but they adapted quickly.
Tangleweb spiders (cobweb spiders)
Members of the family Theridiidae weave irregular, tangled, three-dimensional webs, popularly known as cobwebs. There seems to be an evolutionary trend towards a reduction in the amount of sticky silk used, leading to its total absence in some species. The construction of cobwebs is less stereotyped than that of orb-webs, and may take several days.
OTHER TYPES OF WEBS
The Linyphiidae generally make horizontal but uneven sheets, with tangles of stopping threads above. Insects that hit the stopping threads fall onto the sheet or are shaken onto it by the spider, and are held by sticky threads on the sheet until the spider can attack from below.
EVOLUTION
FOSSIL RECORD
Although the fossil record of spiders is considered poor, almost 1000 species have been described from fossils. Because spiders' bodies are quite soft, the vast majority of fossil spiders have been found preserved in amber. The oldest known amber that contains fossil arthropods dates from 130 million years ago in the Early Cretaceous period. In addition to preserving spiders' anatomy in very fine detail, pieces of amber show spiders mating, killing prey, producing silk and possibly caring for their young. In a few cases, amber has preserved spiders' egg sacs and webs, occasionally with prey attached; the oldest fossil web found so far is 100 million years old. Earlier spider fossils come from a few lagerstätten, places where conditions were exceptionally suited to preserving fairly soft tissues.
The oldest known exclusively terrestrial arachnid is the trigonotarbid Palaeotarbus jerami, from about 420 million years ago in the Silurian period, and had a triangular cephalothorax and segmented abdomen, as well as eight legs and a pair of pedipalps. Attercopus fimbriunguis, from 386 million years ago in the Devonian period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider at the time of its discovery. However, these spigots may have been mounted on the underside of the abdomen rather than on spinnerets, which are modified appendages and whose mobility is important in the building of webs. Hence Attercopus and the similar Permian arachnid Permarachne may not have been true spiders, and probably used silk for lining nests or producing egg-cases rather than for building webs. The largest known fossil spider as of 2011 is the araneid Nephila jurassica, from about 165 million years ago, recorded from Daohuogo, Inner Mongolia in China. Its body length is almost 25 mm.
Several Carboniferous spiders were members of the Mesothelae, a primitive group now represented only by the Liphistiidae. The mesothelid Paleothele montceauensis, from the Late Carboniferous over 299 million years ago, had five spinnerets. Although the Permian period 299 to 251 million years ago saw rapid diversification of flying insects, there are very few fossil spiders from this period.
The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appear in the Triassic well before 200 million years ago. Some Triassic mygalomorphs appear to be members of the family Hexathelidae, whose modern members include the notorious Sydney funnel-web spider, and their spinnerets appear adapted for building funnel-shaped webs to catch jumping insects. Araneomorphae account for the great majority of modern spiders, including those that weave the familiar orb-shaped webs. The Jurassic and Cretaceous periods provide a large number of fossil spiders, including representatives of many modern families.
FAMILY TREE
It is now agreed that spiders (Araneae) are monophyletic (i.e., members of a group of organisms that form a clade, consisting of a last common ancestor and all of its descendants). There has been debate about what their closest evolutionary relatives are, and how all of these evolved from the ancestral chelicerates, which were marine animals. The cladogram on the right is based on J. W. Shultz' analysis (2007). Other views include proposals that: scorpions are more closely related to the extinct marine scorpion-like eurypterids than to spiders; spiders and Amblypygi are a monophyletic group. The appearance of several multi-way branchings in the tree on the right shows that there are still uncertainties about relationships between the groups involved.
Arachnids lack some features of other chelicerates, including backward-pointing mouths and gnathobases ("jaw bases") at the bases of their legs; both of these features are part of the ancestral arthropod feeding system. Instead, they have mouths that point forwards and downwards, and all have some means of breathing air. Spiders (Araneae) are distinguished from other arachnid groups by several characteristics, including spinnerets and, in males, pedipalps that are specially adapted for sperm transfer.
TAXONOMY
Spiders are divided into two suborders, Mesothelae and Opisthothelae, of which the latter contains two infraorders, Mygalomorphae and Araneomorphae. Nearly 46,000 living species of spiders (order Araneae) have been identified and are currently grouped into about 114 families and about 4,000 genera by arachnologists.
WIKIPEDIA
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Spiders (order Araneae) are air-breathing arthropods that have eight legs and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of November 2015, at least 45,700 spider species, and 114 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.
Anatomically, spiders differ from other arthropods in that the usual body segments are fused into two tagmata, the cephalothorax and abdomen, and joined by a small, cylindrical pedicel. Unlike insects, spiders do not have antennae. In all except the most primitive group, the Mesothelae, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.
Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of glands. Spider webs vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-web spiders. Spider-like arachnids with silk-producing spigots appeared in the Devonian period about 386 million years ago, but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years ago, and are very similar to the most primitive surviving suborder, the Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appeared in the Triassic period, before 200 million years ago.
A herbivorous species, Bagheera kiplingi, was described in 2008, but all other known species are predators, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lassoing it with sticky bolas, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the genus Portia show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, and they liquefy their food by flooding it with digestive enzymes and grinding it with the bases of their pedipalps, as they do not have true jaws.
Male spiders identify themselves by a variety of complex courtship rituals to avoid being eaten by the females. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the widow spiders, to co-operative hunting and food-sharing. Although most spiders live for at most two years, tarantulas and other mygalomorph spiders can live up to 25 years in captivity.
While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticides. Spider silk provides a combination of lightness, strength and elasticity that is superior to that of synthetic materials, and spider silk genes have been inserted into mammals and plants to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and mythology symbolizing various combinations of patience, cruelty and creative powers. An abnormal fear of spiders is called arachnophobia.
DESCRIPTION
BODY PLAN
Spiders are chelicerates and therefore arthropods. As arthropods they have: segmented bodies with jointed limbs, all covered in a cuticle made of chitin and proteins; heads that are composed of several segments that fuse during the development of the embryo.[7] Being chelicerates, their bodies consist of two tagmata, sets of segments that serve similar functions: the foremost one, called the cephalothorax or prosoma, is a complete fusion of the segments that in an insect would form two separate tagmata, the head and thorax; the rear tagma is called the abdomen or opisthosoma. In spiders, the cephalothorax and abdomen are connected by a small cylindrical section, the pedicel. The pattern of segment fusion that forms chelicerates' heads is unique among arthropods, and what would normally be the first head segment disappears at an early stage of development, so that chelicerates lack the antennae typical of most arthropods. In fact, chelicerates' only appendages ahead of the mouth are a pair of chelicerae, and they lack anything that would function directly as "jaws". The first appendages behind the mouth are called pedipalps, and serve different functions within different groups of chelicerates.
Spiders and scorpions are members of one chelicerate group, the arachnids. Scorpions' chelicerae have three sections and are used in feeding. Spiders' chelicerae have two sections and terminate in fangs that are generally venomous, and fold away behind the upper sections while not in use. The upper sections generally have thick "beards" that filter solid lumps out of their food, as spiders can take only liquid food. Scorpions' pedipalps generally form large claws for capturing prey, while those of spiders are fairly small appendages whose bases also act as an extension of the mouth; in addition, those of male spiders have enlarged last sections used for sperm transfer.
In spiders, the cephalothorax and abdomen are joined by a small, cylindrical pedicel, which enables the abdomen to move independently when producing silk. The upper surface of the cephalothorax is covered by a single, convex carapace, while the underside is covered by two rather flat plates. The abdomen is soft and egg-shaped. It shows no sign of segmentation, except that the primitive Mesothelae, whose living members are the Liphistiidae, have segmented plates on the upper surface.
Like other arthropods, spiders are coelomates in which the coelom is reduced to small areas round the reproductive and excretory systems. Its place is largely taken by a hemocoel, a cavity that runs most of the length of the body and through which blood flows. The heart is a tube in the upper part of the body, with a few ostia that act as non-return valves allowing blood to enter the heart from the hemocoel but prevent it from leaving before it reaches the front end. However, in spiders, it occupies only the upper part of the abdomen, and blood is discharged into the hemocoel by one artery that opens at the rear end of the abdomen and by branching arteries that pass through the pedicle and open into several parts of the cephalothorax. Hence spiders have open circulatory systems. The blood of many spiders that have book lungs contains the respiratory pigment hemocyanin to make oxygen transport more efficient.
Spiders have developed several different respiratory anatomies, based on book lungs, a tracheal system, or both. Mygalomorph and Mesothelae spiders have two pairs of book lungs filled with haemolymph, where openings on the ventral surface of the abdomen allow air to enter and diffuse oxygen. This is also the case for some basal araneomorph spiders, like the family Hypochilidae, but the remaining members of this group have just the anterior pair of book lungs intact while the posterior pair of breathing organs are partly or fully modified into tracheae, through which oxygen is diffused into the haemolymph or directly to the tissue and organs. The trachea system has most likely evolved in small ancestors to help resist desiccation. The trachea were originally connected to the surroundings through a pair of openings called spiracles, but in the majority of spiders this pair of spiracles has fused into a single one in the middle, and moved backwards close to the spinnerets. Spiders that have tracheae generally have higher metabolic rates and better water conservation. Spiders are ectotherms, so environmental temperatures affect their activity.
FEEDING, DIGESTION AND EXCRETION
Uniquely among chelicerates, the final sections of spiders' chelicerae are fangs, and the great majority of spiders can use them to inject venom into prey from venom glands in the roots of the chelicerae. The family Uloboridae has lost its venom glands, and kills its prey with silk instead. Like most arachnids, including scorpions, spiders have a narrow gut that can only cope with liquid food and spiders have two sets of filters to keep solids out. They use one of two different systems of external digestion. Some pump digestive enzymes from the midgut into the prey and then suck the liquified tissues of the prey into the gut, eventually leaving behind the empty husk of the prey. Others grind the prey to pulp using the chelicerae and the bases of the pedipalps, while flooding it with enzymes; in these species, the chelicerae and the bases of the pedipalps form a preoral cavity that holds the food they are processing.
The stomach in the cephalothorax acts as a pump that sends the food deeper into the digestive system. The mid gut bears many digestive ceca, compartments with no other exit, that extract nutrients from the food; most are in the abdomen, which is dominated by the digestive system, but a few are found in the cephalothorax.
Most spiders convert nitrogenous waste products into uric acid, which can be excreted as a dry material. Malphigian tubules ("little tubes") extract these wastes from the blood in the hemocoel and dump them into the cloacal chamber, from which they are expelled through the anus. Production of uric acid and its removal via Malphigian tubules are a water-conserving feature that has evolved independently in several arthropod lineages that can live far away from water,[14] for example the tubules of insects and arachnids develop from completely different parts of the embryo. However, a few primitive spiders, the sub-order Mesothelae and infra-order Mygalomorphae, retain the ancestral arthropod nephridia ("little kidneys"), which use large amounts of water to excrete nitrogenous waste products as ammonia.
CENTRAL NERVOS SYSTEM
The basic arthropod central nervous system consists of a pair of nerve cords running below the gut, with paired ganglia as local control centers in all segments; a brain formed by fusion of the ganglia for the head segments ahead of and behind the mouth, so that the esophagus is encircled by this conglomeration of ganglia. Except for the primitive Mesothelae, of which the Liphistiidae are the sole surviving family, spiders have the much more centralized nervous system that is typical of arachnids: all the ganglia of all segments behind the esophagus are fused, so that the cephalothorax is largely filled with nervous tissue and there are no ganglia in the abdomen; in the Mesothelae, the ganglia of the abdomen and the rear part of the cephalothorax remain unfused.
Despite the relatively small central nervous system, some spiders (like Portia) exhibit complex behaviour, including the ability to use a trial-and-error approach.
SENSE ORGANS
EYES
Most spiders have four pairs of eyes on the top-front area of the cephalothorax, arranged in patterns that vary from one family to another. The pair at the front are of the type called pigment-cup ocelli ("little eyes"), which in most arthropods are only capable of detecting the direction from which light is coming, using the shadow cast by the walls of the cup. However, the main eyes at the front of spiders' heads are pigment-cup ocelli that are capable of forming images. The other eyes are thought to be derived from the compound eyes of the ancestral chelicerates, but no longer have the separate facets typical of compound eyes. Unlike the main eyes, in many spiders these secondary eyes detect light reflected from a reflective tapetum lucidum, and wolf spiders can be spotted by torch light reflected from the tapeta. On the other hand, jumping spiders' secondary eyes have no tapeta. Some jumping spiders' visual acuity exceeds by a factor of ten that of dragonflies, which have by far the best vision among insects; in fact the human eye is only about five times sharper than a jumping spider's. They achieve this by a telephoto-like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow.
There are spiders with a reduced number of eyes, of these those with six-eyes are the most numerous and are missing a pair of eyes on the anterior median line, others species have four-eyes and some just two. Cave dwelling species have no eyes, or possess vestigial eyes incapable of sight.
OTHER SENSES
As with other arthropods, spiders' cuticles would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. In fact, spiders and other arthropods have modified their cuticles into elaborate arrays of sensors. Various touch sensors, mostly bristles called setae, respond to different levels of force, from strong contact to very weak air currents. Chemical sensors provide equivalents of taste and smell, often by means of setae. Pedipalps carry a large number of such setae sensitive to contact chemicals and air-borne smells, such as female pheromones. Spiders also have in the joints of their limbs slit sensillae that detect forces and vibrations. In web-building spiders, all these mechanical and chemical sensors are more important than the eyes, while the eyes are most important to spiders that hunt actively.
Like most arthropods, spiders lack balance and acceleration sensors and rely on their eyes to tell them which way is up. Arthropods' proprioceptors, sensors that report the force exerted by muscles and the degree of bending in the body and joints, are well understood. On the other hand, little is known about what other internal sensors spiders or other arthropods may have.
LOCOMOTION
Each of the eight legs of a spider consists of seven distinct parts. The part closest to and attaching the leg to the cephalothorax is the coxa; the next segment is the short trochanter that works as a hinge for the following long segment, the femur; next is the spider's knee, the patella, which acts as the hinge for the tibia; the metatarsus is next, and it connects the tibia to the tarsus (which may be thought of as a foot of sorts); the tarsus ends in a claw made up of either two or three points, depending on the family to which the spider belongs. Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, spiders and a few other groups still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors. The only extensor muscles in spider legs are located in the three hip joints (bordering the coxa and the trochanter). As a result, a spider with a punctured cephalothorax cannot extend its legs, and the legs of dead spiders curl up. Spiders can generate pressures up to eight times their resting level to extend their legs, and jumping spiders can jump up to 50 times their own length by suddenly increasing the blood pressure in the third or fourth pair of legs. Although larger spiders use hydraulics to straighten their legs, unlike smaller jumping spiders they depend on their flexor muscles to generate the propulsive force for their jumps.
Most spiders that hunt actively, rather than relying on webs, have dense tufts of fine hairs between the paired claws at the tips of their legs. These tufts, known as scopulae, consist of bristles whose ends are split into as many as 1,000 branches, and enable spiders with scopulae to walk up vertical glass and upside down on ceilings. It appears that scopulae get their grip from contact with extremely thin layers of water on surfaces. Spiders, like most other arachnids, keep at least four legs on the surface while walking or running.
SILK PRODUCTION
The abdomen has no appendages except those that have been modified to form one to four (usually three) pairs of short, movable spinnerets, which emit silk. Each spinneret has many spigots, each of which is connected to one silk gland. There are at least six types of silk gland, each producing a different type of silk.
Silk is mainly composed of a protein very similar to that used in insect silk. It is initially a liquid, and hardens not by exposure to air but as a result of being drawn out, which changes the internal structure of the protein. It is similar in tensile strength to nylon and biological materials such as chitin, collagen and cellulose, but is much more elastic. In other words, it can stretch much further before breaking or losing shape.
Some spiders have a cribellum, a modified spinneret with up to 40,000 spigots, each of which produces a single very fine fiber. The fibers are pulled out by the calamistrum, a comb-like set of bristles on the jointed tip of the cribellum, and combined into a composite woolly thread that is very effective in snagging the bristles of insects. The earliest spiders had cribella, which produced the first silk capable of capturing insects, before spiders developed silk coated with sticky droplets. However, most modern groups of spiders have lost the cribellum.
Tarantulas also have silk glands in their feet.
Even species that do not build webs to catch prey use silk in several ways: as wrappers for sperm and for fertilized eggs; as a "safety rope"; for nest-building; and as "parachutes" by the young of some species.
REPRODUCTION AND LIFE CYCLE
Spiders reproduce sexually and fertilization is internal but indirect, in other words the sperm is not inserted into the female's body by the male's genitals but by an intermediate stage. Unlike many land-living arthropods, male spiders do not produce ready-made spermatophores (packages of sperm), but spin small sperm webs on to which they ejaculate and then transfer the sperm to special syringe-like structures, palpal bulbs or palpal organs, borne on the tips of the pedipalps of mature males. When a male detects signs of a female nearby he checks whether she is of the same species and whether she is ready to mate; for example in species that produce webs or "safety ropes", the male can identify the species and sex of these objects by "smell".
Spiders generally use elaborate courtship rituals to prevent the large females from eating the small males before fertilization, except where the male is so much smaller that he is not worth eating. In web-weaving species, precise patterns of vibrations in the web are a major part of the rituals, while patterns of touches on the female's body are important in many spiders that hunt actively, and may "hypnotize" the female. Gestures and dances by the male are important for jumping spiders, which have excellent eyesight. If courtship is successful, the male injects his sperm from the palpal bulbs into the female's genital opening, known as the epigyne, on the underside of her abdomen. Female's reproductive tracts vary from simple tubes to systems that include seminal receptacles in which females store sperm and release it when they are ready.
Males of the genus Tidarren amputate one of their palps before maturation and enter adult life with one palp only. The palps are 20% of male's body mass in this species, and detaching one of the two improves mobility. In the Yemeni species Tidarren argo, the remaining palp is then torn off by the female. The separated palp remains attached to the female's epigynum for about four hours and apparently continues to function independently. In the meantime, the female feeds on the palpless male. In over 60% of cases, the female of the Australian redback spider kills and eats the male after it inserts its second palp into the female's genital opening; in fact, the males co-operate by trying to impale themselves on the females' fangs. Observation shows that most male redbacks never get an opportunity to mate, and the "lucky" ones increase the likely number of offspring by ensuring that the females are well-fed. However, males of most species survive a few matings, limited mainly by their short life spans. Some even live for a while in their mates' webs.
Females lay up to 3,000 eggs in one or more silk egg sacs, which maintain a fairly constant humidity level. In some species, the females die afterwards, but females of other species protect the sacs by attaching them to their webs, hiding them in nests, carrying them in the chelicerae or attaching them to the spinnerets and dragging them along.
Baby spiders pass all their larval stages inside the egg and hatch as spiderlings, very small and sexually immature but similar in shape to adults. Some spiders care for their young, for example a wolf spider's brood cling to rough bristles on the mother's back, and females of some species respond to the "begging" behaviour of their young by giving them their prey, provided it is no longer struggling, or even regurgitate food.
Like other arthropods, spiders have to molt to grow as their cuticle ("skin") cannot stretch. In some species males mate with newly molted females, which are too weak to be dangerous to the males. Most spiders live for only one to two years, although some tarantulas can live in captivity for over 20 years.
SIZE
Spiders occur in a large range of sizes. The smallest, Patu digua from Colombia, are less than 0.37 mm in body length. The largest and heaviest spiders occur among tarantulas, which can have body lengths up to 90 mm and leg spans up to 250 mm.
ECOLOGY AND BEHAVIOR
NON-PREDATORY FEEDING
Although spiders are generally regarded as predatory, the jumping spider Bagheera kiplingi gets over 90% of its food from fairly solid plant material produced by acacias as part of a mutually beneficial relationship with a species of ant.
Juveniles of some spiders in the families Anyphaenidae, Corinnidae, Clubionidae, Thomisidae and Salticidae feed on plant nectar. Laboratory studies show that they do so deliberately and over extended periods, and periodically clean themselves while feeding. These spiders also prefer sugar solutions to plain water, which indicates that they are seeking nutrients. Since many spiders are nocturnal, the extent of nectar consumption by spiders may have been underestimated. Nectar contains amino acids, lipids, vitamins and minerals in addition to sugars, and studies have shown that other spider species live longer when nectar is available. Feeding on nectar avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes.
Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages.
METHODS OF CAPTURING PREY
The best-known method of prey capture is by means of sticky webs. Varying placement of webs allows different species of spider to trap different insects in the same area, for example flat horizontal webs trap insects that fly up from vegetation underneath while flat vertical webs trap insects in horizontal flight. Web-building spiders have poor vision, but are extremely sensitive to vibrations.
Females of the water spider Argyroneta aquatica build underwater "diving bell" webs that they fill with air and use for digesting prey, molting, mating and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling.
Net-casting spiders weave only small webs, but then manipulate them to trap prey. Those of the genus Hyptiotes and the family Theridiosomatidae stretch their webs and then release them when prey strike them, but do not actively move their webs. Those of the family Deinopidae weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs' area by a factor of up to ten. Experiments have shown that Deinopis spinosus has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of Deinopis subrufa appears to live mainly on tipulid flies that they catch with the backwards strike.
Mature female bolas spiders of the genus Mastophora build "webs" that consist of only a single "trapeze line", which they patrol. They also construct a bolas made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromones of moths, and then swing the bolas at the moths. Although they miss on about 50% of strikes, they catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas. Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract moth flies, and catch them with their front pairs of legs.
The primitive Liphistiidae, the "trapdoor spiders" of the family Ctenizidae and many tarantulas are ambush predators that lurk in burrows, often closed by trapdoors and often surrounded by networks of silk threads that alert these spiders to the presence of prey. Other ambush predators do without such aids, including many crab spiders, and a few species that prey on bees, which see ultraviolet, can adjust their ultraviolet reflectance to match the flowers in which they are lurking. Wolf spiders, jumping spiders, fishing spiders and some crab spiders capture prey by chasing it, and rely mainly on vision to locate prey.Some jumping spiders of the genus Portia hunt other spiders in ways that seem intelligent, outflanking their victims or luring them from their webs. Laboratory studies show that Portia's instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly how to overcome new prey species. However, they seem to be relatively slow "thinkers", which is not surprising, as their brains are vastly smaller than those of mammalian predators.
Ant-mimicking spiders face several challenges: they generally develop slimmer abdomens and false "waists" in the cephalothorax to mimic the three distinct regions (tagmata) of an ant's body; they wave the first pair of legs in front of their heads to mimic antennae, which spiders lack, and to conceal the fact that they have eight legs rather than six; they develop large color patches round one pair of eyes to disguise the fact that they generally have eight simple eyes, while ants have two compound eyes; they cover their bodies with reflective hairs to resemble the shiny bodies of ants. In some spider species, males and females mimic different ant species, as female spiders are usually much larger than males. Ant-mimicking spiders also modify their behavior to resemble that of the target species of ant; for example, many adopt a zig-zag pattern of movement, ant-mimicking jumping spiders avoid jumping, and spiders of the genus Synemosyna walk on the outer edges of leaves in the same way as Pseudomyrmex. Ant-mimicry in many spiders and other arthropods may be for protection from predators that hunt by sight, including birds, lizards and spiders. However, several ant-mimicking spiders prey either on ants or on the ants' "livestock", such as aphids. When at rest, the ant-mimicking crab spider Amyciaea does not closely resemble Oecophylla, but while hunting it imitates the behavior of a dying ant to attract worker ants. After a kill, some ant-mimicking spiders hold their victims between themselves and large groups of ants to avoid being attacked.
DEFENSE
There is strong evidence that spiders' coloration is camouflage that helps them to evade their major predators, birds and parasitic wasps, both of which have good color vision. Many spider species are colored so as to merge with their most common backgrounds, and some have disruptive coloration, stripes and blotches that break up their outlines. In a few species, such as the Hawaiian happy-face spider, Theridion grallator, several coloration schemes are present in a ratio that appears to remain constant, and this may make it more difficult for predators to recognize the species. Most spiders are insufficiently dangerous or unpleasant-tasting for warning coloration to offer much benefit. However, a few species with powerful venoms, large jaws or irritant hairs have patches of warning colors, and some actively display these colors when threatened.
Many of the family Theraphosidae, which includes tarantulas and baboon spiders, have urticating hairs on their abdomens and use their legs to flick them at attackers. These hairs are fine setae (bristles) with fragile bases and a row of barbs on the tip. The barbs cause intense irritation but there is no evidence that they carry any kind of venom. A few defend themselves against wasps by including networks of very robust threads in their webs, giving the spider time to flee while the wasps are struggling with the obstacles. The golden wheeling spider, Carparachne aureoflava, of the Namibian desert escapes parasitic wasps by flipping onto its side and cartwheeling down sand dunes.
SOZIAL SPIDERS
A few spider species that build webs live together in large colonies and show social behavior, although not as complex as in social insects. Anelosimus eximius (in the family Theridiidae) can form colonies of up to 50,000 individuals. The genus Anelosimus has a strong tendency towards sociality: all known American species are social, and species in Madagascar are at least somewhat social. Members of other species in the same family but several different genera have independently developed social behavior. For example, although Theridion nigroannulatum belongs to a genus with no other social species, T. nigroannulatum build colonies that may contain several thousand individuals that co-operate in prey capture and share food. Other communal spiders include several Philoponella species (family Uloboridae), Agelena consociata (family Agelenidae) and Mallos gregalis (family Dictynidae). Social predatory spiders need to defend their prey against kleptoparasites ("thieves"), and larger colonies are more successful in this. The herbivorous spider Bagheera kiplingi lives in small colonies which help to protect eggs and spiderlings. Even widow spiders (genus Latrodectus), which are notoriously cannibalistic, have formed small colonies in captivity, sharing webs and feeding together.
WEB TYPES
There is no consistent relationship between the classification of spiders and the types of web they build: species in the same genus may build very similar or significantly different webs. Nor is there much correspondence between spiders' classification and the chemical composition of their silks. Convergent evolution in web construction, in other words use of similar techniques by remotely related species, is rampant. Orb web designs and the spinning behaviors that produce them are the best understood. The basic radial-then-spiral sequence visible in orb webs and the sense of direction required to build them may have been inherited from the common ancestors of most spider groups. However, the majority of spiders build non-orb webs. It used to be thought that the sticky orb web was an evolutionary innovation resulting in the diversification of the Orbiculariae. Now, however, it appears that non-orb spiders are a sub-group that evolved from orb-web spiders, and non-orb spiders have over 40% more species and are four times as abundant as orb-web spiders. Their greater success may be because sphecid wasps, which are often the dominant predators of spiders, much prefer to attack spiders that have flat webs.
ORB WEBS
About half the potential prey that hit orb webs escape. A web has to perform three functions: intercepting the prey (intersection), absorbing its momentum without breaking (stopping), and trapping the prey by entangling it or sticking to it (retention). No single design is best for all prey. For example: wider spacing of lines will increase the web's area and hence its ability to intercept prey, but reduce its stopping power and retention; closer spacing, larger sticky droplets and thicker lines would improve retention, but would make it easier for potential prey to see and avoid the web, at least during the day. However, there are no consistent differences between orb webs built for use during the day and those built for use at night. In fact, there is no simple relationship between orb web design features and the prey they capture, as each orb-weaving species takes a wide range of prey.
The hubs of orb webs, where the spiders lurk, are usually above the center, as the spiders can move downwards faster than upwards. If there is an obvious direction in which the spider can retreat to avoid its own predators, the hub is usually offset towards that direction.
Horizontal orb webs are fairly common, despite being less effective at intercepting and retaining prey and more vulnerable to damage by rain and falling debris. Various researchers have suggested that horizontal webs offer compensating advantages, such as reduced vulnerability to wind damage; reduced visibility to prey flying upwards, because of the back-lighting from the sky; enabling oscillations to catch insects in slow horizontal flight. However, there is no single explanation for the common use of horizontal orb webs.
Spiders often attach highly visible silk bands, called decorations or stabilimenta, to their webs. Field research suggests that webs with more decorative bands captured more prey per hour. However, a laboratory study showed that spiders reduce the building of these decorations if they sense the presence of predators.
In 1973, Skylab 3 took two orb-web spiders into space to test their web-spinning capabilities in zero gravity. At first, both produced rather sloppy webs, but they adapted quickly.
Tangleweb spiders (cobweb spiders)
Members of the family Theridiidae weave irregular, tangled, three-dimensional webs, popularly known as cobwebs. There seems to be an evolutionary trend towards a reduction in the amount of sticky silk used, leading to its total absence in some species. The construction of cobwebs is less stereotyped than that of orb-webs, and may take several days.
OTHER TYPES OF WEBS
The Linyphiidae generally make horizontal but uneven sheets, with tangles of stopping threads above. Insects that hit the stopping threads fall onto the sheet or are shaken onto it by the spider, and are held by sticky threads on the sheet until the spider can attack from below.
EVOLUTION
FOSSIL RECORD
Although the fossil record of spiders is considered poor, almost 1000 species have been described from fossils. Because spiders' bodies are quite soft, the vast majority of fossil spiders have been found preserved in amber. The oldest known amber that contains fossil arthropods dates from 130 million years ago in the Early Cretaceous period. In addition to preserving spiders' anatomy in very fine detail, pieces of amber show spiders mating, killing prey, producing silk and possibly caring for their young. In a few cases, amber has preserved spiders' egg sacs and webs, occasionally with prey attached; the oldest fossil web found so far is 100 million years old. Earlier spider fossils come from a few lagerstätten, places where conditions were exceptionally suited to preserving fairly soft tissues.
The oldest known exclusively terrestrial arachnid is the trigonotarbid Palaeotarbus jerami, from about 420 million years ago in the Silurian period, and had a triangular cephalothorax and segmented abdomen, as well as eight legs and a pair of pedipalps. Attercopus fimbriunguis, from 386 million years ago in the Devonian period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider at the time of its discovery. However, these spigots may have been mounted on the underside of the abdomen rather than on spinnerets, which are modified appendages and whose mobility is important in the building of webs. Hence Attercopus and the similar Permian arachnid Permarachne may not have been true spiders, and probably used silk for lining nests or producing egg-cases rather than for building webs. The largest known fossil spider as of 2011 is the araneid Nephila jurassica, from about 165 million years ago, recorded from Daohuogo, Inner Mongolia in China. Its body length is almost 25 mm.
Several Carboniferous spiders were members of the Mesothelae, a primitive group now represented only by the Liphistiidae. The mesothelid Paleothele montceauensis, from the Late Carboniferous over 299 million years ago, had five spinnerets. Although the Permian period 299 to 251 million years ago saw rapid diversification of flying insects, there are very few fossil spiders from this period.
The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appear in the Triassic well before 200 million years ago. Some Triassic mygalomorphs appear to be members of the family Hexathelidae, whose modern members include the notorious Sydney funnel-web spider, and their spinnerets appear adapted for building funnel-shaped webs to catch jumping insects. Araneomorphae account for the great majority of modern spiders, including those that weave the familiar orb-shaped webs. The Jurassic and Cretaceous periods provide a large number of fossil spiders, including representatives of many modern families.
FAMILY TREE
It is now agreed that spiders (Araneae) are monophyletic (i.e., members of a group of organisms that form a clade, consisting of a last common ancestor and all of its descendants). There has been debate about what their closest evolutionary relatives are, and how all of these evolved from the ancestral chelicerates, which were marine animals. The cladogram on the right is based on J. W. Shultz' analysis (2007). Other views include proposals that: scorpions are more closely related to the extinct marine scorpion-like eurypterids than to spiders; spiders and Amblypygi are a monophyletic group. The appearance of several multi-way branchings in the tree on the right shows that there are still uncertainties about relationships between the groups involved.
Arachnids lack some features of other chelicerates, including backward-pointing mouths and gnathobases ("jaw bases") at the bases of their legs; both of these features are part of the ancestral arthropod feeding system. Instead, they have mouths that point forwards and downwards, and all have some means of breathing air. Spiders (Araneae) are distinguished from other arachnid groups by several characteristics, including spinnerets and, in males, pedipalps that are specially adapted for sperm transfer.
TAXONOMY
Spiders are divided into two suborders, Mesothelae and Opisthothelae, of which the latter contains two infraorders, Mygalomorphae and Araneomorphae. Nearly 46,000 living species of spiders (order Araneae) have been identified and are currently grouped into about 114 families and about 4,000 genera by arachnologists.
WIKIPEDIA
DEL PAPEL AL MURAL
Por: Pegatina Criolla
“La hoja de papel que se convierte en un mural”
La hoja de papel que deja de ser un simple soporte blanco inerte para darle paso a un muro de concreto con una infinita gama de colores que habla por si solo así este no pronuncie ninguna palabra, no es necesario, que vive por si solo, que se alimenta de las miradas de los desconocidos, que mira desde lo mas alto una ciudad que esta en constante cambio.
El muralismo ha mutado a pasos agigantados, paso de ser un arte de artistas revolucionarios enclaustrados en sus talleres armados de escaleras, andamios, brochas, vinilos y pinceles a convertirse en un movimiento contemporáneo de artistas emergentes que han utilizado este medio para transcender con su mensaje y dejar un legado a través de sus piezas.
La ciudad ha cambiado y con ella sus diferentes espacios una y mil historias que empieza en una hoja de papel se transforma en un mural, una pieza, una producción, una ilustración, un graffiti o una frase.
“MUROS EN BLANCO MENTES VACÍAS” anónimo
El pintar un mural es un oficio de tiempo completo riguroso que demanda no solo tiempo sino también mucha dosis de paciencia, constancia, disciplina y sobre todo de gusto: “no es pintar por pintar.” No es salir a las calles a rayar como muchos piensan, esto es una profesión seria con mucha proyección.
Transformar espacios efímeros en verdaderas piezas de arte , es una de las labores del muralista quien eligió este medio para expresar una posición ya sea critica o de cambio social y sobretodo poder compartir con la gente su propia visión de un mundo ideal.
El pintar es como cocinar debe saber de los ingredientes, debe conocer la receta, debe tener las herramientas necesarias para cocinar, debe tener un equipo que lo apoyen para así deleitar con un gran plato a los comensales en este caso a los transeúntes quienes son nuestro curadores y nuestros mejores críticos.
Todo tiene más sentido cuando el dibujo hecho en una hoja de papel o en cualquier otra superficie pasa a un muro de varias dimensiones, esas pequeñas y livianas líneas de grafito se convierten en grandes trazos de pintura, en manchas de colores, en formas reales o en muchos casos en surrealismos plasmados en cuadriculas proporcionales que dejen en evidencia el expresionismo de cada artista.
Estructuras lineales hechas con un pincel, bocetos en libretas, horas de trabajo, el reporte del clima, curso de alturas, los transeúntes expectantes, las acciones sociales, maquinaria pesada, la comunidad, el equipo de trabajo, varios colores, las experiencias, la fotografía, los festivales, la pintura, las reacciones, los extensores hechos con palos de escoba, las anécdotas, los presupuesto, los proyectos, las promesas, la gestión y sobre todo la satisfacción propia son lo que alimentan la llama viva del muralismo y hace que creamos en esta expresión que esta cogiendo cada vez más fuerza que empezó siendo un simple dibujo en una hoja de papel.
Un diumenge al matí, sense cap espectativa, mig aburrit em truca una bona amiga i em diu : Vols venir fins el Sitjar a fer fotos a les flors?,,. Era una bona proposta, a més no en tenia cap altra.
Ara ja era un diumenge al matí engrescador, lluminós i amb molt bones espectatives.
El Sitjar és un centre de jardinaria que hi ha al sortir del poble, de Salt. A vegades anem lluny i no recordem el que tenim a prop.
A part de flors hi vaig trobar un ambient ben agradable, donant-nos totes les facilitats per poder disfrutar com nens petits fent fotos a les flors i a tot allò que volguèssim.
Em vaig proposar apropar-m'hi força, intentar disfrutar de cada detall, entrant en les intimitats de les flors.
Aquí en teniu una mostra.
A més les estaven regant i tenien gotetes d'aigua que encara feia més interessant intentar les fotos.
Ara puc dir que va ser una diumenge al matí molt aprofitar, amb alegria i molt ben estar, Un diumenge al matí lluminós, ben acompanyat i fent una activitat engrescadora.
Ja veieu com pot canviar un matí només que tingueu la sort de tenir bons amics i bones amigues,
Big huge thanks to Vega for planning a shoot with all of us dressed up as lil fairy nymphs!
Read more and See more of the shoot @ My Way
And big thanks to Minnu as well for her kind heart and incredible talent! Muas~
Skin : LOLA pale-makeup7 | LeLutka
Eye : Planets - Jupiter | LG Boutique
Nails : Gift White Nails | MAI
Lash : Twiggy | Redgrave
Hair : MOA 02 Light Platinum Blonde | 69
Ears : Plain Elf Ears FrontFlop | Mynerva
Wings : LUNATICA Wings | Beauty Avatar | Glam Affair *no longer sold*
Top : PETA White | Glam Affair
Dress : Petiole Dress | Equus
Jewelry : Nizam White | Zaara
Aristobia approximator ♀
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Apilado de 20 tomas con el Sigma 150mm y el anillo extensor Zuiko de 25mm.
"Convertendo e mudando a leitura!", 04 fotografias. Usei a Canon 60D e objetiva 18x55mm (padrão).
"Converting and changing reading!", 04 photographs. I used Canon 60D and 18x55mm lens (standard).Todos os direitos reservados para Vivaldo Armelin Júnior.
The night on June 14 was spetacular, so I decided to try something.
I have an old and low budget setup here:
Skywatcher 102mm f13 Maksutov-Cassegrain
Webcam SPC900NC (Yeap... REALLY old)
Barlow SmartAstronomy 2.5xApo
I used a 5cm tube extensor as well, after the barlow.
WxAstroCapture to record the AVI files, AS!2 to stack and Registax for wavelets.
My considerations: I DO need a bigger telescope and a better camera. 😅
Toma realizada con Nikon D5100
Lente Nikon 35 mm f/2.0
Anillo extensor de 28 mm
Adorama rieles de macro enfoque de 4 vias.
Nikon D5100
Nikon 35 mm f/2.0
28 mm's extending ring
Adorama macro focusing rail set, 4 way.
Takahashi FC76 DCU + Takahashi Modulo Q (Extensor 1.7x)
Filtro Solar Thousand Oaks
Canon 60D
Montura Nexstar SE
Composición de 23 fotos durante el eclipse, con un intervalo de 10 minutos entre cada una. Cada foto:
Exposición: 1/60
Iso: 250
Distancia Focal: 969 mm.
F: 12.7
Procesado: Lightroom + Ps
Guillermo Cervantes Mosqueda
Observatorio Astronómico Altaïr
Poncitlán Jalisco México
El pequeño caracol se ríe de su destino paseando al filo de un tenedor, las formas puntiagudas tanto del tenedor como la del caparazón del caracol.
CÓMO LA HICE:
Es muy similar a la imagen anterior, objetivo inverso canon 50mm f1,8 a diafragma f22, fuelle extensor, flash externo y una gran dosis de paciencia.
La universidad es mentira. El campo te enseña a compartir la fruta y verdura con tu vecino.
Manifiesto por un espacio abandonado. Pintura plástica en extensores apilados de 5 metros sobre muros en ruinas
Cam : fuji finepix s5700 / extensor 210mm ( F: 16 / V : 1/250 )
Fondo : lamina de plastico amerilado naranja
Flash : ng: 12 mas ( relleno positivo )
Acsesorio: filtro gris graduado ( factor 1/2 )
Tecnica : diafragmacion (efecto estrellado ) y compensacion de la exposicion ( 1.1/2 F) Macro relacion .( 5:1 ) diametro vaquita : 2mm
Fotografia y ediccion : Neon
serie de postales navideñas , diambulando entre sacrilegia fina estricta , de elementos acordes a la circunstancia como que un caballo cabellarero que vuele con una crewde renos magicos reno king de nariz roja prendida alviento.
don gordo rojo pascuero desiende con dificultad sus chimeneas , regaloxxx deja ,come galletas leche , y plaf
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postales navideñas a $2.500 incluye tarjetita y afiche a elecciòn .
9.4071844
zaines326@gmail.com
lovelordruls.
xxxns.