Black Flies


  • Latin Name: Simuliidae
  • Size: 1/8”
  • Color: Black, gray or yellow
  • Shape: Black flies appear to have a humped back because of the way their head is tilted down. Their antennae have 11 segments and they have clear wings.
  • Found in: All over the United States
  • Overview: There are over 1800 species of black flies, which are all members of the Simuliidae family. Black flies are also referred to as buffalo gnats and are particularly bothersome to humans and livestock in the spring and summer.

Origin: Unknown
Climate: Black flies are able to live anywhere there is a flowing water source. The majority of black fly species are found in semitropical climates where they can survive outdoors all year.
Favorite Foods: Male black flies eat nectar. Female black flies like blood. Depending on the species of female black fly, they may prefer bird blood to human blood. Larvae eat algae and bacteria from the water.
Family: Female black flies lay eggs in rivers and streams. They will lay between 150 and 500 eggs during their lifetime. The white eggs can be placed on a rock or vegetation or just dropped into the flowing current. The water must be warm for the larvae to hatch. Once hatched, the brown larvae will attach to rocks and gather food from a fan near their mouth that expands to catch debris from the water. They will molt six times before entering the pupal stage. After a few days, the black fly will emerge from the case and fly away to mate. An adult fly will live up to three months.
Unique Facts: Males are not bloodsuckers. Some species of female black flies need blood before they can lay their eggs. Black flies do not bite at night. A black fly’s saliva is toxic and can cause an itchy allergic reaction in some. They typically bite the neck or ear – areas not covered by clothing. They are also attracted to perfume and the carbon dioxide we exhale.  Black flies can kill farm animals by causing anaphylactic shock or suffocation.
Signs of a problem: If you live near a river or stream, you are most likely familiar with black flies in the spring and summer. You may see swarms flying together during the day especially on sunny humid days.
Do they attack humans? Females attack humans by biting and sucking blood. A female may fly up to 10 miles away from the water source in search of a meal. Males may still cause a disturbance as they interrupt outside activities. Black flies are the most active during the day. They will not bite at night and do not like to fly on windy days. Black flies can spread disease when they bite and are most well known for transporting river blindness in Africa.
Stopping an infestation: It is extremely hard to treat an infestation because eggs are in the water and putting chemicals into the rivers and streams is illegal in most areas. Adult flies don’t live very long and can be kept at bay by insect repellent with DEET, but you will need to reapply more frequently than you do with mosquitos. Yard fogging isn’t an ideal solution because the flies will not reproduce in your yard unless you have a river or stream. A pest professional will need a license to treat the water with an organic substance. It is recommended to wear long sleeves and pants as well as protective headgear if you will be in an area highly infested during the afternoon.

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