Is it a hare's ear? Or a woolly bugger? Maybe its a crayfish? At the end of the day, it's big, it's nasty and it catches fish - bass, trout, carp, panfish - anything that likes a big buggy meal.
Perdigon variants in multiple colours are a great go-to for euro-nymphing in both local waters, and those further afield. Tungsten gets you down quick and the glossy body has the extra bit of flash to get the trout's attention.