Black flies, belonging to the Simuliidae family, are small, dark insects recognized by their distinctive humpbacked appearance. Over 2,200 species have been identified worldwide. These insects typically thrive in areas with flowing water, such as streams and rivers, where their larvae develop. While often a nuisance, their presence is sometimes considered an indicator of good water quality due to the larvae’s oxygen requirements.
Understanding the Need for a Blood Meal
Only female black flies bite as part of their reproductive cycle. The blood meal provides essential protein and nutrients for egg production. Without this intake, egg development cannot occur. This is a biological necessity for reproduction.
Both male and female black flies primarily feed on nectar for energy. For the female, obtaining a blood meal is necessary before laying her 150 to 500 eggs. This biological requirement explains why these insects seek out mammals and birds, including humans.
How Black Flies Locate Their Targets
Black flies use sensory mechanisms to locate hosts. They are particularly drawn to the carbon dioxide (CO2) exhaled by breathing animals and humans. This chemical cue serves as a primary long-range attractant.
Beyond carbon dioxide, black flies also detect body heat emitted by warm-blooded creatures. Closer to a host, specific body odors like perspiration and lactic acid become important attractants. Visual cues, like dark-colored clothing, also draw black flies, helping them pinpoint a target.
The Mechanics of the Bite and Its Aftermath
Black flies do not possess piercing mouthparts like mosquitoes; instead, they have specialized cutting structures. Their mandibles and maxillae, which are blade-like, work together to lacerate the skin. This cutting action creates an open wound, allowing blood to pool.
Once the cut is made, the black fly injects saliva into the wound. This saliva contains compounds that facilitate blood feeding. These include anticoagulants, which prevent the blood from clotting, and vasodilators, which widen blood vessels to increase blood flow to the site. The saliva also contains components that may have anesthetic properties, potentially numbing the area, allowing the fly to feed undetected for a short period.
The aftermath of a black fly bite involves localized reactions. The foreign proteins introduced by the fly’s saliva trigger an immune response in the host. This response often results in swelling, redness (erythema), and intense itching around the bite site. In some individuals, these reactions can be more severe, leading to pronounced localized dermatitis or hypersensitivity responses.