Black Fly


Actual Size: 1 to 5 mm

Characteristics: Black, with some gray and possibly reddish color.

Legs: 6

Antennae: Yes

Wings: Yes

Habitat: Most common near slow-moving sources of water, such as streams.


  • Breeds in slow running water.
  • Only the females are blood feeders and will readily bite.
  • Reactions to black fly bites are collectively known as “black fly fever.”

Black Flies in San Angelo

Black flies are small, blood-sucking insects commonly found in various parts of the United States and Canada. This pest goes by different names, including buffalo gnats and turkey gnats. They are notorious for flying around people’s heads and can occasionally get into eyes and ears or crawl into the hair. It’s important to note that only the female black flies are blood feeders, and they will readily bite both humans and animals to obtain a blood meal.

During late spring and early summer, especially in the more northern latitudes, black flies may appear in large numbers. Their presence can be particularly troublesome during this time, making outdoor activities challenging in heavily infested areas.

Black Fly Habitat

Black flies have a unique breeding habitat, as they exclusively breed in running water. The larvae and pupae of black flies develop in flowing water that is typically non-polluted and has a high level of dissolved oxygen. It’s important to note that black fly larvae thrive in oxygenated water sources, which means that adult black flies are usually found near slow-moving streams, creeks, or rivers where the immature stages develop.

The term “flowing water” doesn’t necessarily mean white water rapids; instead, it indicates that the water must be in motion. Lakes and ponds with stagnant water are unsuitable for black fly development as they require the continuous flow of water for their life cycle.

Black Fly Behaviors, Threats, or Dangers

Black flies can indeed be bothersome biting pests, but fortunately, in the U.S., they are not known to transmit diseases to humans. However, the bites of black flies can trigger various reactions in humans, ranging from a small puncture wound at the site of the original blood meal to more severe swelling, sometimes reaching the size of a golf ball. Collectively, these reactions to black fly bites are known as “black fly fever” and may include symptoms like headaches, nausea, fever, and swollen lymph nodes in the neck.

Although black flies do not pose a direct health threat to humans, they can be a nuisance, and they can transmit diseases to animals or livestock. While these diseases do not affect humans, they can cause serious health issues for animals.

If you are dealing with a black fly problem on your property, contact your local fly exterminators.