No, I can't explain it. No, it doesn't look like any insect I've ever seen. And no, I wouldn't leave home without a few in my fly box. You shouldn't either.
The Purple Chubby, like most flies in my personal "Golden Fly Box,"earned a spot by producing when nothing else would, or at least not at the same level. I was fishing the Big Hole River in Montana with my friend Joe Begin from Winston Rods a few years ago when this funny looking fly made me look good. There had been a Salmonfly hatch the week before, but the big bugs had come and gone. Remembering something my friend Jeff Perin had said about the effectiveness of the pattern after the hatch, I tyed on a Purple Chubby and crushed it. The fishing, not the fly.
Since then, I have found that it works well before, during, and after the big bugs fade from the bushes. Fish it alone or as a hopper/dropper combo throughout the spring and early summer, but keep it handy as a general attractor pattern all year round. Purple is the new tan, and it works.
Hook: TMC 5212 Sz 10
Tail: UV Pearl Krystal Flash
Body: Purple Ice Dub
Under Wing: Black 2mm Fly Foam
Wing: Silver Gray EP Fiber