Diura bicaudata, Southerndale Beck, 13 May 19 (1 of 4)
Diura bicaudata stonefly by Southerndale Beck near Skiddaw, 13 May 19.
As the forecast for the day was very promising I thought I'd have a third go at collecting a Diura bicaudata stonefly from a suitable lakeland site, ie a stony stream at an altitude of over 300m. Southerndale Beck between Skiddaw and Ullock Pike seemed like a good choice as there's a convenient parking spot near High Side and it's only a 35-minute drive away.
Despite the fact that there's no footpath it turned out to be an excellent route and it was possible to follow the stream quite closely, and check out the rocks along most of the climb, without too much difficulty (see later photos). Although it took over three hours, I did eventually find a single specimen at an altitude of 385m - and on this occasion it stayed put for long enough for me to get a decent in situ shot before ushering it into a container (Photo 1).
The remaining photos were taken later in the day using the integral camera on my SX10D microscope. Photo 2 includes a length measurement, Photo 3 shows the head/pronotum and a dorsal view of the end of the abdomen, and Photo 4 both of the forewings.
Note on identification: Identified as a Perlodidae from Hynes (Ref 1) which unlike the simplified AIDGAP key avoids reference to wings for this species. Colouring and the fact that the male is not fully winged and the tenth tergum is not longitudinally divided means that the specimen must be either Perlodes mortoni or Diura bicaudata. The dorsal view of the lower abdomen (Photo 3, right) is a decent match to that shown in Hynes Fig 16E for the latter and differs noticeably for that shown in Fig 16C for the former. Both forewings are shown in Photo 4 and neither is a good overall match to either of the reference sketches shown in Figures 6B and 6D for the two species. However, in the area of interest (tip of the wing near the costa) Diura bicaudata is judged to be the better fit. Finally, the altitude of the sighting is consistent with the Hynes specification for Diura bicaudata, ie above 1000ft (305m), but marginally beyond the limit specified for Perlodes mortoni, ie up to about 1200 ft (366m).
Ref 1: H B N Hynes "A Key to the Adults and Nymphs of the British Stoneflies (Plecoptera)", Freshwater Biological Association, Scientific Publication No 17, 1958.
Diura bicaudata, Southerndale Beck, 13 May 19 (1 of 4)
Diura bicaudata stonefly by Southerndale Beck near Skiddaw, 13 May 19.
As the forecast for the day was very promising I thought I'd have a third go at collecting a Diura bicaudata stonefly from a suitable lakeland site, ie a stony stream at an altitude of over 300m. Southerndale Beck between Skiddaw and Ullock Pike seemed like a good choice as there's a convenient parking spot near High Side and it's only a 35-minute drive away.
Despite the fact that there's no footpath it turned out to be an excellent route and it was possible to follow the stream quite closely, and check out the rocks along most of the climb, without too much difficulty (see later photos). Although it took over three hours, I did eventually find a single specimen at an altitude of 385m - and on this occasion it stayed put for long enough for me to get a decent in situ shot before ushering it into a container (Photo 1).
The remaining photos were taken later in the day using the integral camera on my SX10D microscope. Photo 2 includes a length measurement, Photo 3 shows the head/pronotum and a dorsal view of the end of the abdomen, and Photo 4 both of the forewings.
Note on identification: Identified as a Perlodidae from Hynes (Ref 1) which unlike the simplified AIDGAP key avoids reference to wings for this species. Colouring and the fact that the male is not fully winged and the tenth tergum is not longitudinally divided means that the specimen must be either Perlodes mortoni or Diura bicaudata. The dorsal view of the lower abdomen (Photo 3, right) is a decent match to that shown in Hynes Fig 16E for the latter and differs noticeably for that shown in Fig 16C for the former. Both forewings are shown in Photo 4 and neither is a good overall match to either of the reference sketches shown in Figures 6B and 6D for the two species. However, in the area of interest (tip of the wing near the costa) Diura bicaudata is judged to be the better fit. Finally, the altitude of the sighting is consistent with the Hynes specification for Diura bicaudata, ie above 1000ft (305m), but marginally beyond the limit specified for Perlodes mortoni, ie up to about 1200 ft (366m).
Ref 1: H B N Hynes "A Key to the Adults and Nymphs of the British Stoneflies (Plecoptera)", Freshwater Biological Association, Scientific Publication No 17, 1958.