Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
This wild-looking little thing completely puzzled me. At first I was thinking beetle or month larva, until I got a look at the pictures on the computer screen. I made a couple of incorrect guesses before entomologist Greg Courtney pointed me in the right direction with Psychodidae. He suggested a possible genus of Thornburghiella, but could not rule out some other members of the tribe Pericomini.
These widely varied terrestrial insects sometimes accidentally jump into trout streams. I have heard of trout being selective to them, but it is not very common. Anglers often call them jassids.
They are very small and are best imitated on hooks sized 22 or smaller. They can be treated the same, from the angler's point of view, as the Cicadellidae family of tree hoppers.
Start a Discussion of Membracidae
References
Swisher, Doug and Carl Richards. 2000. Selective Trout. The Lyons Press.