Make sure you rinse them first.. I've read in old fishkeeping books that said fish love the stuff... It's just a too messy and smelly to collect them unless you raise them in a sterile environment like how you would raise mealworms. I've never used them.
if they are clean most species of fish i've offered them too snapped them up like candy.
I've been pondering how to raise them in a clean'ish medium. Downside is flies are one of nature's creatures that give me serious willies. I'll handle pretty much anything but i really dont like them .
Mostly cause they land on crap then my food....that really annoys me. But i have used larva for small fish before and had a great reception to it .