Corixa booby (small).
Sometimes, when they're really fussy, you have to drop sizes - even in April.
This is a smaller version of the Corixa Booby. I've tied it short on a 16. In order to fish smallish flies like this effectively you'll need to go as light as a five or six weight.
Also works as a summer dry fly of course. Notice how scruffy it is, difficult to achieve that bit.
Tying instructions:
Size 16, debarb, tie in strip of black ethafoam at bend. Seal fur body (black), rib, pull foam back over and tie off. Pantone the back in black.