Category 3 Blowfly

Foam, and a fine wire hook on purpose

Built out of foam rather than hair, which means it floats high and keeps floating after a fish has chewed it. It sits on a fine wire hook, and that is deliberate: fine wire is light enough not to drag a foam fly down at the front. The maker's own note is that big trout have bent one on him but never broken one. Easy to see on the water, which matters more with a blowfly than with most things, because they get eaten fast.