No-see-um

No-see-ums are tiny biting flies, also called biting midges, punkies or sand flies, small enough to pass through regular window screens. Females bite for blood, leaving sharp, burning bites and itchy red welts, mostly near water at dawn and dusk. The one thing to do: wear a repellent and long sleeves at dawn and dusk near water, and use 30-by-30 mesh screens at home.

This page covers how to identify no-see-ums and their bites, where they breed and how to avoid them. It rests on NC State Extension and University of Arizona Cooperative Extension guidance.

How to Identify No-See-Ums: Barely Visible Biters

• Tiny: often under 1/16 inch; NC State says some are only 0.5 mm long.
• Gray to dark brown, short and stocky, with clear or spotted wings; under a microscope they look like miniature mosquitoes.
• Bites feel sharp and burning, and itchy red welts about 1/8 inch across, or small water-filled blisters, appear afterward (University of Arizona).
• Swarms on calm, humid evenings and mornings, near water.

A no-see-um (left) next to a mosquito, both biting at once. Note how much smaller it is. Photo: Dunpharlain (CC BY-SA 4.0), via Wikimedia Commons.

No-See-Ums vs. Look-Alikes: Bites You Can’t Explain

If you’re bitten outdoors near a marsh or beach by something you can’t see, it’s most likely a biting midge. Other bite patterns are compared in bug bite pictures.

Where No-See-Ums Breed: Wet Mud and Moist Organic Matter

• Coastal marshes, beaches and mangroves; storm-tossed seaweed on beaches is ideal breeding ground (NC State)
• Ponds, streams, springs, river banks and wet, muddy ground
• Over-irrigated lawns, poorly drained splash pads and indoor potted plants (University of Arizona)
• Porches and patios near these areas at dawn and dusk

Larvae live in mud, sand or wet soil and can’t survive drying out completely or more than about 2 inches of water.

When You’ll See Them: Summer, at Dawn and Dusk

They’re most numerous in summer, and year-round where winters are warm. Most activity is at dawn and dusk. Larvae usually spend winter in the mud and develop for 6 months to a year; adults live about a month, and females take several blood meals (NC State).

Are No-See-Ums Harmful? Painful, Itchy Bites

Their bites are painful and itchy and can bring allergic reactions; welts or blisters that break open can become infected if scratched. In the US they aren’t a major source of human disease, though related species spread bluetongue virus in sheep and cattle and cause “sweet itch” in horses (University of Arizona).

How to Confirm It’s No-See-Ums

1. Note the time and place: dawn or dusk, near water or wet ground.
2. Look for tiny flies on skin with a magnifier; they look like miniature mosquitoes.
3. Check the bites: small red welts or blisters that itch intensely.
4. Rule out the house: no pets, no bed bug signs and bites only after time outdoors point to biting midges.

What to Do: Repel, Cover, Screen

Avoid the dawn and dusk hours near water, wear light-colored long sleeves, pants and socks, add a hat with fine mesh netting over the face and neck, and use a repellent that works on mosquitoes; it also works on biting midges. NC State says children and pregnant women should use repellents sparingly. Run fans on porches, since no-see-ums are weak fliers. Standard 16-by-16 and 18-by-16 screens let them through, so the University of Arizona suggests 30-by-30 mesh where possible. Keep doors shut rather than propped open, and check screens for rips and gaps. If bites cluster around wet spots at home, hold off irrigating and let the area dry, which kills eggs and larvae. NC State says sprays and fogs work only briefly, because more midges move in once the spray clears. For other pests, browse all pest guides.