The female Deer-Horse Fly are bloodsucking and the bites can be very painful. They can be serious pests of livestock and humans. The males are found on flowers and feed only on nectar and pollen. The adults are often seen around swamps, marshes, and ponds.
The larvae are aquatic and are mostly found in shallow water or moist soil. Most of the larvae are predaceous.
Some deer-horse fly transmits diseases such as tularemia and anthrax in the United States and Africa. These flies are medium to large-sized with stout bodies. The eyes are often brightly colored with a pattern of stripes. The eyes touch each other on the top of the head in males and are separated in the females.
Deer flies are up to 12 mm long, a bit larger than houseflies but still smaller than horse flies. They are black and yellow, black or sometimes grey. Their wings are cross-banded with black stripes, and their eyes are brightly colored (gold, green, orange, or blue). The genus name Chrysops, in fact, is derived from the Greek word chrysos, which literally means gold eyes.
Female flies require blood in order to make viable eggs. Reproduction is not possible without this. Typically, females wait in shady areas for a possible prey to pass by, a deer, cattle, other large undulates, and of course humans. They always seem to go for that spot you can’t reach and when one bites you, you know it.
Horsefly females are also very aggressive blood feeders. although the males do not bite but instead feed on pollen and plant nectar. Female horse flies usually bite large, stationary animals, attacking the legs or body. Horseflies have a range of animals that they bite, this includes livestock, humans, pets, and birds.