Black flies belong to the insect family Simuliidae. These small, robust flies are found globally and are a recognized nuisance due to the biting habits of the females. They are significant pests, often associated with areas near moving water.
Identifying Features of the Adult Fly
Adult black flies are small, typically measuring between 1 and 5 millimeters in length, giving them a gnat-like appearance. Their coloration ranges from black or dark gray, though some species exhibit shades of yellow or orange. They have a robust body shape.
The most recognizable feature is the distinctly arched thoracic region, which gives the insect a characteristic “humped” back. This prominent structure is why they are colloquially referred to as “buffalo gnats.” They possess short, stout legs and a small head with relatively large compound eyes.
Black flies have broad, clear, gauzy wings that lack scales or hairs, unlike mosquitoes. The wings feature prominent, thickened veins concentrated along the anterior edge. Their antennae are short and segmented.
Habitat and Activity Patterns
The black fly life cycle is strongly tied to aquatic environments, specifically running water sources. Females lay eggs on submerged objects in fast-moving water, such as rivers and streams. The larvae require clean, well-oxygenated water to develop and do not breed in stagnant ponds or lakes.
Adult flies emerge from these waterways, but their activity is confined to specific times of the year and day. Black fly season is concentrated in the early spring and summer months, depending on the geographic location and water temperature. They are active during daylight hours, with biting activity peaking in the morning and late afternoon.
These flies are primarily outdoor pests and do not pursue hosts inside buildings or homes. They are strong fliers and can travel several miles from their aquatic breeding sites in search of a meal. Their presence is a reliable indicator that a source of flowing water is nearby.
Why Black Flies Are Noticed
Black flies are notorious because the female requires a blood meal to produce eggs. Unlike many other biting insects that pierce the skin, the female uses specialized, razor-like mouthparts to cut the skin’s surface. This action causes localized bleeding, and the fly then laps up the pooled blood.
The fly’s saliva contains an anticoagulant, which keeps the blood flowing while she feeds. This feeding mechanism results in a bite that bleeds more and produces a more intense reaction than a mosquito bite. The bite site commonly develops swelling and itching that can persist for several days.
In some individuals, reactions to the saliva can be systemic, a condition called “black fly fever.” Symptoms include headache, nausea, fever, and swelling of the lymph nodes in the neck. Black flies swarm around the head and face, frequently targeting the ears, hairline, and exposed skin, making them persistent and irritating pests during outdoor activities.