I Wonder Why I Swallowed That Fly...

Why do trout prefer one insect over another? According to one UK paper it could simply be a matter of taste.

"...Of course, I said, part of the reason had to be the huge feeding opportunity that the big fly presents. The sheer size of the fly, when coupled with its profusion, gave the trout the biggest and easiest meal of the year at a time when it was still regaining condition.
"Ah, yes," OGrady said. "But there's another reason. They have to like it, you know. It tastes so good."

Yep, you guessed it. He had given them a taste test. Now that's what I call a hard core angler.