Tungsten bead Black or copper slotted tungsten bead (1, sized to hook)
Chenille or floss Chartreuse fine chenille (short length for the peeping larva)
Hare's ear dubbing (guard hairs left in) Natural brown hare s mask dubbing (a rough pinch for the case)
Copper wire Copper wire (small, for the rib)
Hungarian partridge Brown hen hackle (1 feather for the legs)
Hare's mask or ostrich herl Dark brown/black dubbing (a small pinch for the head)
How to tie it
Slide the tungsten bead to the eye and start brown thread behind it, running a base back to the bend. This fly imitates a cased caddis with the grub peeking out, so the case fills most of the shank.
At the bend, tie in the copper wire, then dub a fat, deliberately shaggy hare's-ear body forward over the rear two-thirds of the shank to build the bulky stick-and-sand case.
Counter-wrap the copper rib forward in 4-5 open turns to armor the case, tie off, and rake the dubbing with a bodkin so it looks rough and grubby, not neat.
Just behind the bead, tie in a short length of chartreuse chenille or floss and wrap a small, bright segment for the peeping larva head poking out the front of the case. This bright spot is the trigger.
Fold a partridge feather and take 1-2 turns of soft hackle over the chartreuse for legs, sweeping fibers back to about one hook gap.
Dub or wind a small dark hare/ostrich head over the last turns behind the bead, whip finish, and add a drop of cement.