Adult flies are unique in the insect world because they have only two flight wings. This may be difficult to see with the naked eye, but a good magnifying glass can help you distinguish a fly from other insects. Look for where the wings attach to determine if there are two points of attachment or more. Biting flies come in a variety of sizes and shapes.
The immature stages of flies are maggots: eyeless, legless, worm-like organisms. Fly pupae, the stage between maggots and adults, are typically brown, cylindrical and cigar-shaped. Because of where biting flies breed, it is not common to see the larvae and pupal stages, except for mosquitoes, which breed in any standing water.
Because of their blood-feeding habits, biting flies represent a risk to human health.
Mosquitoes are well-known vectors of pathogens, and other biting flies transmit pathogens to people and animals around the world.
In addition, biting flies can cause painful and irritating welts after taking a blood meal, and scratching these bite sites can lead to infection of the bite site if fingernails or skin are not clean.
In the case of black flies, some people have strong reactions to their bite and saliva, which can result in headache, fever, nausea, swollen lymph nodes in the neck, and allergic dermatitis.
Biting flies develop outdoors, where larvae breed in moist or wet conditions. The adults feed on blood and are therefore attracted to people and other animals. Knowing the types of conditions preferred by each species can help you identify and possibly manage the source.
Deer and Horse Flies
Larvae develop in moist to wet soils, with some species living in water.
Adult flies rest on plants in shady areas during the day and wait for a host they either see or smell (carbon dioxide we exhale or body odors). Adults are most active in the morning and evening.
Larvae breed in moist, decaying organic matter, including the mud found around hay ring feeding troughs on farms.
Adults are active during the day – feeding primarily in the early morning and late afternoon. Stable flies found in coastal areas are typically blown there from nearby farmland.
Larvae develop in clean, flowing water sources, and adults are found near these streams, creeks or rivers in open or wooded areas.
Adults flies are capable of traveling several miles away from breeding sites to find hosts.
Looking for detailed information? Mosquitoes have a page specifically dedicated to these notorious pests.
No-See-Ums - aka Biting Midges
Larvae require moisture for their development, and breed on the shores of streams, ponds, in muddy soils and tree holes.
Adults will not be found far from breeding sites, are small enough to pass through typical window screening, and are attracted to lights at night. During summer months, ‘mystery bites’ could come from no-see-ums that enter the home through open windows.
The challenge with biting fly management is that treating habitats where larvae develop is not feasible. This is due to the abundance of natural breeding sites and the difficulty of treating areas near water. Therefore, management of biting flies often relies on reducing the number of adults through trapping, or avoidance. Because of differences in biology, specific trap types are needed for the different biting fly pests.
Deer and Horse Flies
Traps designed for these pests tend to focus on agricultural areas where flies attack livestock. You can learn more about the different trap types from this University of Florida factsheet.
In New York, these flies are a problem in agricultural settings where they develop in leftover plant material from crops and animal feed. Specialized sticky trap monitors can be used to reduce numbers. Plant residue, mud and other breeding sites can be altered to dry substrate and kill larvae. Additional options for management include biological control, and treating resting surfaces with insecticides. Information on stable fly management is available from the Livestock and Field Crops Program.
These flies are active certain times of year, primarily spring, and are best avoided by wearing head protection and clothing that covers the skin. Black flies preferentially attack the head, so protection of the face, ears and hair may be necessary. Based on the problems these flies impose, some municipalities treat streams using biopesticides.
An important consideration with these small flies is exclusion for indoor areas. Due to their small size, these flies can pass through standard window screening. Therefore, 16-mesh or smaller is recommended to exclude no-see-ums (NOTE: smaller window screen sizes will reduce airflow).
Protective Clothing: You can generally avoid biting flies by wearing clothing that covers the skin – especially for outdoor activities such as hiking in wooded areas. Light-weight, long-sleeved clothing is available from many retailers of sporting goods.
Repellants: Insect repellents can help you to avoid some biting flies. However, some flies are attracted to you by looks alone (a moving object), so repellents may not be completely effective. Learn more about selecting an appropriate repellent:
Fans: Some biting flies are not strong flyers, and may be discouraged with the use of powerful fans, either overhead or ground-level.