Deer flies can transmit a rare bacterial infection called tularemia, or rabbit fever, according to Healthline. This infection causes skin ulcers, headaches and fevers and can be fatal if left untreated. Tularemia is treatable using antibiotics.
Deer flies are typically about a 1/4 to 1/2 inch long and tend to live near lakes, swamps and pools, according to Healthline. The wings of deer flies have brown and black bands on them, and the flies often have green or yellow eyes.
Although deer flies are commonly seen on hot summer days, they are usually more active during spring. Regardless of the season, deer flies are traditionally more active during the day and become less active during the night. Deer flies feed on the blood of humans and animals.
Deer flies can be avoided by spraying the body and clothing with insect repellent containing Deet when the flies are present, according to the University of Kentucky College of Agriculture, Food and Environment. In most areas, deer flies are only a problem for small stretches throughout the summer months and typically only feed during the day.
