Black Flies

Black fly illustration
Black fly illustration
Black fly on human skin
Black fly on human skin
black fly larvae
mosquitoes and black flies in the sky
bug bite

Also known as buffalo gnats and several other common names, black flies are true flies found in areas with cool-water rivers and streams. Unlike mosquitoes, which lay eggs near stagnant water, black flies prefer running water. The larvae develop attached to submerged rocks and wood. When larvae mature into flying adults, hordes of biting black flies leave people, pets and wildlife with painful, throbbing, itching wounds. Depending on the species, several generations can occur each year. In some regions, black fly season stretches from spring to fall.

Black Fly Identification

Black flies are small, dark, sturdy flies that typically range between 1/20 and 1/3 inch in length. Viewed from the side, they have a very distinct humpback thorax, much like the hump on a buffalo's back. Their wormlike, legless larvae look similar to mosquito larvae, but they have a swollen posterior that gives them a "bowling pin" look. Adults congregate in shady, low-lying areas with poor air circulation and heavy vegetation — including bountiful gardens.

Signs or Damage of Black Flies

Black flies don't damage garden plants; they harm people and animals instead. Some species are primarily nuisances that fly into ears, mouths and eyes, but others are very aggressive biters when seeking the blood meals they need to reproduce. Their unusual, blade-like mouthparts slash into skin rather than piercing it. Human reactions include headaches, nausea, fever and swollen lymph nodes. Children and small animals are especially at risk.

How to Control Black Flies

Adult black flies can fly several miles, so infestations around homes happen even when rivers and streams aren't nearby. Cool, damp gardens become hiding places for clouds of these biting pests. GardenTech brand offers these highly effective options to kill black flies by contact and keep protecting for up to three months:

  • Sevin Insect Killer Concentrate provides an easy, economical way to treat larger areas. Use the convenient measuring cap with a pump-style sprayer, and spray all lawn and garden surfaces thoroughly. This non-staining formula also treats your home's foundation up to a height of 3 feet.
  • Sevin Insect Killer Ready to Spray attaches directly to a normal garden hose and does the mixing and measuring for you as you spray. Treat foundations up to a maximum height of 3 feet with this non-staining formula. Spray lawn and garden areas thoroughly.

Black Fly Control Tip: Avoid wearing dark-colored clothing around black flies; it may attract these pests. For optimal results, treat for black flies during early morning hours or right before sunset. Black flies are most active at these times.

Always read product labels thoroughly and follow instructions, including guidelines for listed plants and pests, application frequencies and pre-harvest intervals (PHI) for edible crops.

Photo Credit:

D. Sikes (CC BY-SA 2.0)

D. Sikes (CC BY-SA 2.0)

Whitney Cranshaw, Colorado State University, (CC By 3.0 US)

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