This common name refers to only one family.
These are pretty much always called Ants.
Ants are one of the best-known terrestrial (Terrestrial: Insects which live on land and are fed on by trout only when they incidentally fall into the water are known as "terrestrials" to fly anglers, and they're very important in late summer.) food sources for trout. Wingless ants often stumble by accident into the water, making them a very common "occasional" item on the trout's menu. Imitations of these unlucky critters make excellent searching patterns (Searching pattern: Any artificial fly pattern used when trout that aren't feeding selectively on anything in particular. A searching pattern may be an attractor or an imitation of something specific that the fish might favor even though it's not currently hatching.) in mid- to late summer.
The real fun with ants, however, comes from the mating swarms of winged species. They are spotty and hard to predict, but when they happen to fall over the water they can draw more trout activity than all but the best hatches of huge mayflies.
Formicidae (Ants) Ant Adult
View 7 PicturesI collected this flying ant from the surface of a popular Catskill trout stream, where its species prompted steady rising from selective trout for several late-morning hours. It was mixed with smaller ants of a different color, and I photographed one of them too.