During the larval stage, which lasts one to three years,[4] they feed on small creatures or rotting organic matter near or in the water.

[5] When feeding, the females use scissor-like mandibles and maxillae to make a cross-shaped incision and then lap up the blood.

Anti-coagulants in the saliva of the fly prevents blood from clotting and may cause severe allergic reactions.

Parasites and diseases transmitted by the deer fly include tularemia, anthrax, anaplasmosis, equine infectious anemia, hog cholera, and filiariasis.

[2] Trapping devices and protective clothing, such as long-sleeved shirts and hats, can help avoid the annoyance and bites of aggressive deer flies.