Midges Flies and Mosquitoes: Diptera

Physical characteristics: Adult big black horse flies are large, heavy-bodied flies and measure 0.35 to 1.1 inches (9 to 28 millimeters) in length. Their wide heads have bulging, brightly colored eyes. The thorax or midsection is gray, while the abdomen is black. The wings are blackish. The larvae are cylinder-shaped and have fine wrinkles along the length of the body.

Geographic range: This species is found in western Canada and the United States, from British Columbia south to California, east to Kansas and Texas.

Habitat: Adults live near ponds, streams, and marshes, while the larvae develop in mud or moist soil along the edges of these habitats.

Adult big black horse flies eat mostly nectar and pollen. Females require a blood meal before they can lay eggs. They suck blood from livestock and humans. (Illustration by Jonathan Higgins. Reproduced by permission.)

Diet: Adults eat mostly nectar and pollen. Females require a blood meal before they can lay eggs. They suck blood from livestock and humans. The larvae prey on other insect larvae, snails, and earthworms.

Behavior and reproduction: Females land on exposed skin to feed. They lay up to one thousand eggs in masses three or four layers deep. The masses are laid on leaves, rocks, or other objects near water or moist areas and are covered with a jellylike material. Hatching larvae fall into the water or on moist soil. They pupate at the margins of pools or other drier areas in the habitat.

Big black horse flies and people: Horse flies are a nuisance to horses and mules because of the painful bites of the female. They will also bite people.

Conservation status: This species is not considered endangered or threatened. ∎