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When an Insect - Spiders, too - triggers those tiny red hairs on the inner lobes of a Venus Flytrap (see inset), the Trap snaps shut capturing a tasty morsel. It'll struggle a bit but inexorably our Insect will be caught up in a tightening, barred cell. There are just enough of those triggers to ensure that it's really an insect that's alighted on that lobe and not some little piece of detritus.
Our Caught Spider was unwisely spinning her web on Venus's 'teeth'; you can see part of it on the left. Somehow Ariadne must have lost her own thread and venturing 'south' triggered those hairs. Prisoner! and soon to be dissolved for a meal by Venus's enzymatic secretions. So far so bad for her; so far so good for Venus...
Or is it really good for Lady Trap? In this case: nope. Her Trigger Hairs felt bigger than her stomach. Ariadne is rather too big for her; body parts are sticking out from Venus's prison. Those spider legs can't be covered in 'antiseptic' digestive fluid. They're open to the air and to the manifold fungi and bacteria that dispose of dead insects. Soon those body parts will turn black, and in turn they'll infect pretty Green Trap, turning her Black to Death as well. Retribution for gluttony?...
The modified leaf of Venus-flytrap; when an insect crawls on the surface of the leaf and touches at least two trigger hairs, the two sides of the leaf close and the insect is trapped inside and digested
www.esa.org/esablog/research/strange-but-true-tales-from-...
Dionaea muscipula
I doubt I have to tell anyone what this one is. But I can tell you some things you may not know about them.
First off, if you have one of these, don't try to feed it bologna or any other "meat" that isn't bugs. As I read somewhere once, these evolved in swamps where insects were present, not where cows were tripping and falling in, so their digestive enzymes are geared toward bug protein, not cow protein.
Second, see those trigger hairs? Not the edge points, but the three little dark hairs inside. Those actually need to be touched not just once but twice in succession in order to get the trap to close. This is to prevent false triggers from something like a raindrop, conserving energy for the things that actually have nutritional value.
Pictured here are the hair like triggers and the teeth like cilia that lock in the prey. These grow to an average of 2 1/2" (6.4 cm) tall. Some higher, some lower.
Closing of the trap is triggered by contact with one or more of the hinged trigger hairs twice in succession. The actual closing involves a complex interaction between elasticity, turgor (pressure of the cell contents against the cell wall) and growth.
When I visited the Green Swamp in early May, the leaves on all the Venus Flytrap plants (Dionaea muscipula) were young and fresh. If you look carefully, you can see trigger hairs on the inner surfaces of the traps. (These are far less obvious than the "fingers" along the margins of the leaves.) When an insect walks into the trap and bumps into a trigger hair, the trap closes.
The Green Swamp is located near Wilmington, North Carolina.