There are many kinds of Dung Flies but the most striking is the yellow Dung Fly. This bright yellow, hairy fly is about 3/8” in length. It has dark bristles on long slender legs.
Dung Flies breed in cow, horse, pig, and sheep dung. The larvae of some species live in decaying plant material and can be very abundant in rotting vegetation and mud along shorelines. Most of the small black flies that fly up if you disturb a fresh cow pat are Dung Flies. The common yellow Dung Fly is a typical example of this family and, although their larva feed on the dung, the adults are predatory and feed on other flies which have come to the dung to feed.
Swarms of the furry, golden males collect on steaming, fresh cowpats. The arrival of females is greeted with a flurry of activity and mating pairs can be seen. The eggs are laid in dung. The females prefer fresh cowpats because older ones form a crust and it becomes very difficult for egg laying. As the pat gets older, therefore, fewer and fewer females arrive.
The larvae feed in the dung, eating organic matter and other smaller fly larvae.
Most Black Flies are about 1/8” long, black or grey colored, short legged, stout, and the thorax is strongly convex, giving a humpbacked, gnat-like appearance.
Like mosquitoes, adult female Black Flies feed on blood and are often serious pests. Black Flies often occur in enormous numbers in the spring and early summer months, close to clean, fast-moving rivers and streams where the larvae develop as semi-aquatic insects. They attack people, cattle, horses, deer, birds and other animals and can transmit some diseases.
Black Flies lacerate the skin and suck blood. On people, they crawl into sleeves, under neck bands, around boot tops and other vulnerable places, especially favoring the head just beneath the brim of a hat. Bites can cause swelling and numb soreness for many days. On cattle and horses, the ears seem to be the favorite feeding location. Adult Black Flies are migratory, commonly flying many miles from larval breeding sites. Unlike mosquitoes, Black Flies are day-time feeders. During sunny, warm days, peak attacks occur in mid-morning and then a more intense phase in the evening, ending at dusk.