What is "botflies"

Usage examples of "botflies".

Longtusk saw that it was a mist of life: vast clouds of insects, mosquitoes and blackflies and warble flies and botflies, that rose from the lakes to plague the great herbivores—including himself—and a dreamier cloud of ballooning spiders and wind-borne larvae, riding the breezes to a new land.

So it was easier simply to medicate the horses regularly-but still it seemed to him that it would be better if the botflies never got at the horses in the first place.