These are pretty much always called Garden Hackles.
Earthworms frequently end up in the stream after they make a wrong turn crawling around on a rainy day, and trout relish them. It is interesting that fly fishers frown upon the San Juan Worm, a popular artificial imitaiton, considering that this form of terrestrial hatch-matching is just as rooted in biology as any ant or beetle fisherman's sport.
Since worms fit easily onto a hook, many fishermen skip all the feathers & thread tying and go straight for their favorite all-natural fly pattern: the real, live, wiggling "Garden Hackle."