Biting midges, often called no-see-ums or sand gnats, are tiny bloodsucking flies that slip through standard window screens and end up biting you indoors. Most are less than 1 mm long (roughly 1/24 of an inch), which makes them nearly invisible and small enough to pass through openings that stop every other flying insect. If you’re finding itchy, burning welts but can’t see what’s biting you, midges are a likely culprit.
How Biting Midges Get Inside
Standard window and door screens are designed to block mosquitoes, but their mesh openings are far too large for biting midges. A typical household screen has a mesh of about 18×16, leaving gaps that a 1 mm fly passes through easily. Midges also exploit tears, gaps around screen frames, and poorly sealed doors. They’re most active at dawn and dusk, and they’re strongly drawn to the carbon dioxide you exhale and to indoor lighting, so open windows on a warm evening are an invitation.
Unlike mosquitoes, midges don’t need much of an opening. Even a slight warp in a screen frame or a gap where weatherstripping has worn down can let dozens inside. If you live near standing water, salt marshes, muddy shorelines, or any area with consistently damp soil and decaying organic matter, the source population may be very close to your home.
Where They Breed Near Your Home
Biting midges breed in both salt and freshwater habitats. Their larvae feed on decaying organic matter in mud, wet soil around seepage areas, intertidal sand, and the edges of ponds or drainage ditches. Along coastal areas, seaweed and plant debris that wash ashore after storms create ideal breeding conditions. Inland, any patch of consistently soggy ground with leaf litter or rotting vegetation can support a population.
Midges don’t typically breed indoors unless you have a persistently waterlogged area, like a chronically overwatered planter, a leaky basement drain, or a clogged condensation line creating standing moisture. The vast majority fly in from outside breeding sites within a few hundred meters of your home. Reducing those nearby habitats is one of the most effective long-term strategies.
Keeping Midges Out of Your Home
Upgrade to No-See-Um Screening
The single most effective physical barrier is replacing standard screens with no-see-um mesh. These screens use a much finer weave, typically 20×20 mesh, with apertures as small as 0.0013 inches. That’s tight enough to block midges while still allowing airflow, though visibility and air circulation are somewhat reduced compared to regular screens. A 20×20 fiberglass no-see-um screen has about 45% openness, meaning you’ll still get a reasonable breeze. Options with higher mesh counts (like 20×30) drop to around 32% openness but offer even better protection.
No-see-um screening comes in rolls from 36 to 96 inches wide and can be installed in standard window and door frames. If replacing all your screens isn’t practical, prioritize bedroom windows and any windows you open regularly in the evening. Aluminum versions (24×22 mesh) offer better visibility and durability but cost more.
Seal Gaps and Reduce Light Attraction
Check door sweeps, weatherstripping, and the seals around window-mounted air conditioners. Any gap wider than about half a millimeter is an entry point. Caulk or replace worn seals. At night, switch outdoor lights near doorways to yellow or amber bulbs, which are less attractive to flying insects. If you need to open doors frequently in the evening, a screen door with no-see-um mesh makes a meaningful difference.
Reduce Nearby Breeding Sites
Walk the perimeter of your home and look for areas where soil stays wet. Improve drainage where possible, fix leaking outdoor faucets, and clear leaf litter or decaying plant material from low spots. If you’re near the coast, removing trapped seaweed and organic debris from nearby intertidal areas helps reduce local populations. Emptying saucers under potted plants, cleaning clogged gutters, and eliminating any small pools of standing water all cut down on breeding habitat close to your home.
Repellents That Work on Midges
If midges are getting inside despite your efforts, personal repellents can protect you. DEET-based products (up to 30% concentration) are effective against biting midges. Picaridin works well too, particularly against midges and chiggers, and many people find it less greasy on skin. A plant-derived option containing PMD (the active ingredient in oil of lemon eucalyptus products) is labeled for no-see-ums at concentrations of 8 to 10 percent, though it generally needs more frequent reapplication.
For indoor use, applying repellent to exposed skin before bed is practical if you’re dealing with an active infestation you haven’t yet sealed out. Ceiling fans and portable fans also help: midges are weak fliers, and consistent air movement makes it harder for them to land and bite.
Treating Midge Bites
Midge bites produce small red welts that itch intensely, often more than mosquito bites relative to their size. The itch comes from your immune system reacting to proteins in the midge’s saliva. Some people develop raised bumps that last for days, while others get barely noticeable marks. People who are newly exposed to midges (after moving to a new area, for example) tend to react more strongly than long-term residents.
For immediate relief, apply ice to reduce swelling and calm the itch. Over-the-counter anti-itch creams containing camphor and menthol (0.5%) or a topical anesthetic like pramoxine provide quick, temporary relief and can be reapplied several times a day. Hydrocortisone cream (1% is available without a prescription) helps with persistent itchy bites when applied once daily. Oral antihistamines can reduce itching and swelling, especially if you have multiple bites keeping you awake at night.
Avoid scratching. Midge bites that get scratched open are prone to secondary infection, which turns a minor annoyance into a problem that may need antibiotics. If a bite becomes increasingly red, warm, swollen, or begins oozing after a few days, that’s a sign of infection rather than a normal bite reaction.
When Bites Become Severe
Most midge bites are a nuisance, not a medical concern. However, some people develop exaggerated reactions: large areas of swelling, especially on the hands, feet, or face. For these reactions, oral antihistamines combined with a stronger prescription steroid cream can bring things under control. True allergic reactions to midge bites (difficulty breathing, widespread hives, dizziness) are rare but possible. Anyone who has experienced anaphylaxis from insect bites should carry injectable epinephrine.