Black Flies

These pests are outside the authority of the Vector Control Program. We offer educational information but do not control or regulate these pests. 

Black Fly Facts

Black flies, also known as buffalo gnats, are small humpbacked flies that can come in many different colors including shades of black, brown, gray, and yellow. These flies can be aggressive biters.

Female black flies bite humans, as well as domestic and wild animals. Black flies tend to bite during the day. Certain types of black flies prefer a specific host, but most will prey on a range of hosts. 

Habitat and Life Cycle

Black flies need running water in which to breed. Female black flies lay their eggs on submerged objects in streams such as plants, rocks, twigs, or leaves. The eggs hatch and develop in the water until they are ready to emerge as adults. The complete life cycle from egg to adult can last from 6 to 15 weeks.

Adult black flies can often be seen in swarms in the late spring and early summer. 

Black Fly Prevention and Control 
Fly repellents are somewhat effective in preventing bites but need frequent re-application. It is best to wear pants and long-sleeved shirts in areas with black flies.

Controlling black flies is difficult due to the nature of their breeding sites but there are some products labeled for black fly control. Always follow label instructions.

More information

Nuisance Flies (California Department of Public Health)

Black flies (University of Florida)