> Are deer flies a biting fly? We've got flies that bite, but I am only vaguely aware of the term deer fly.

There are different. There's the horse fly (https://en.wikipedia.org/wiki/Horse-fly) and its related species deer fly (https://en.wikipedia.org/wiki/Deer_fly) And there's the black fly (https://en.wikipedia.org/wiki/Black_fly) which is a different family. They all bite.