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diagram of an insect pointing out the antenna, head, thorax, legs, wings, and abdomen
Flies are the only insects that have two flight wings instead of four as shown in this picture. Illustration: NYSIPM.

What Do Biting Flies Look Like?

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.

Five whiteish, legless, cigar shaped insects on beige background
Fly larvae. Photo: NYSIPM. Click photos to see enlarged versions.

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.

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Should I Worry About Biting Flies?

Because of their blood-feeding habits, biting flies represent a risk to human health.

Disease pathogens

Mosquitoes are well-known vectors of pathogens, and other biting flies transmit pathogens to people and animals around the world.

A robust fly with a  pointed abdomen and very large green eyes with short antennae.
Horse fly. Photo: NYSIPM.

Localized irritation

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.

Allergic reaction

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.

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Why Do I Have Biting Flies?

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

A robust yellow fly on an insect pin with a paper label at the base of the pin.
Deer fly. Photo: NYSIPM

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.

Stable Flies

Three flies are stuck on an adhesive against a white background. One fly has a short, needle-like mouthpart extending outward.
Stable flies. Photo: NYSIPM

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.

Stable flies bite with a needle-like proboscis.

Black Flies

close up of the side view of a long fly with a large red eye, fuzzy, gray thorax, and black abdomen with white stripes sitting on a reflective surface
Black fly. Photo: Whitney Cranshaw, Colorado State University,

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.

Close up of a small fly with mouth parts embedded into skin and a red swollen abdomen
Biting midge. Photo: Whitney Cranshaw, Colorado State University,

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.

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How Do I Get Rid of Biting Flies?

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.

white, opaque plastic covered with dozens of black flies attached to a wooden pole in front of a stone wall
Alsynite biting fly trap. Photo: NYSIPM

Stable Flies

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.

Black Flies

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).

Personal Protection

women standing on cliff edge overlooking a valley wearing net pants over shorts, hiking boots, blue t-shirt, beige vest, and carrying a black shoulder pack.
Clothing made of netting can help protect against biting flies. Photo: NYSIPM

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.

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