No-see-ums (also spelled noseeums or no see ums) are tiny biting midges in the family Ceratopogonidae, most commonly the genus Culicoides. They measure roughly 1 to 3 mm — small enough that you often feel the bite before you can see the insect. In Ontario they breed in wet soil, mud, marsh edges, and moist organic matter, and the biting females swarm near water at dawn and dusk from late spring through summer.

Are no-see-ums the same as biting midges?

Yes. "No-see-um" is the everyday name for biting midges, and both terms refer to the same tiny two-winged flies (family Ceratopogonidae). Regional nicknames include "punkies," "sand flies," and "moose flies." They are not gnats in the true sense, and they are not baby mosquitoes — biting midges are their own group of insects, roughly one-quarter the size of a typical mosquito.

What do no-see-um bites look like compared to mosquito bites?

A no-see-um bite starts as a sharp, burning pinprick, then usually forms a small red dot that can swell into an itchy welt over several hours — often in clusters, because the midges feed in groups. Mosquito bites tend to be a single raised puffy bump that itches quickly. No-see-um bites are frequently found on exposed skin near the hairline, ankles, and wrists, and their itch can linger for days, sometimes longer than a mosquito bite.

Why can no-see-ums get through window and porch screens?

Standard window and door screens use a mesh of roughly 1.1 to 1.5 mm openings, sized to stop houseflies and mosquitoes. No-see-ums are small enough to fly straight through those gaps. To keep them out you need "no-see-um mesh" (sometimes labelled 20x20 mesh or finer, around 0.6 mm openings). It is sold for porches, tents, and RV windows. The trade-off is reduced airflow, so many Ontario homeowners combine fine mesh with a fan on the patio, since midges are weak fliers.

When are no-see-ums worst in Ontario?

Biting midges are most active in Ontario from late May through August, with the heaviest swarms at dawn and dusk on warm, humid, still evenings. They are weak fliers, so calm windless conditions near water — lakeshores, ponds, marshes, ravines, and cottage country — produce the worst bites. A steady breeze or a fan noticeably reduces them. Peak nuisance often overlaps with black fly season in early summer.

What repellent actually works against no-see-ums?

Health Canada registered repellents containing DEET or picaridin (also called icaridin) are effective against biting midges when applied to exposed skin, and oil of lemon eucalyptus is a plant-based option. Because midges target ankles, wrists, and the hairline, cover those areas well. For clothing and gear, permethrin-treated fabric adds a strong barrier. A patio fan and long, light-coloured sleeves at dawn and dusk cut bites further.

How do I get rid of no-see-ums in my yard?

Reduce the moist breeding habitat first: fix drainage so water does not pool, clear soggy leaf litter and thick damp mulch, and keep gutters and low spots draining. Run a fan on seating areas because midges cannot fly against moving air. For heavy or recurring pressure near water, a professional barrier treatment applied to shaded vegetation, damp edges, and resting sites knocks down the adult population where it rests during the day.

Are no-see-um bites dangerous in Ontario?

For most people in Ontario, no-see-um bites are an itchy nuisance rather than a health threat — the biting midges here are not significant disease carriers of human illness the way some tropical species are. The main issues are intense itching, clustered welts, and occasional allergic reactions or secondary infection from scratching. If a bite area becomes very swollen, spreading, or infected, see a healthcare provider.

No-See-Ums & Biting Midges in Ontario: Bites, Screens & Control

Feature	No-see-um (biting midge)	Mosquito
Insect size	Tiny — about 1–3 mm	Larger — about 6–15 mm
First sensation	Sharp, burning pinprick	Often unnoticed until it itches
Bite appearance	Small red dot → itchy welt, often clustered	Single raised puffy bump
Number of bites	Frequently many in one area	Usually one or a few, spread out
Common bite spots	Ankles, wrists, hairline, exposed skin	Any exposed skin
Itch duration	Can linger days; sometimes intense	Typically eases in a day or two
Sound	Silent — no whine	Audible high-pitched whine
Peak activity	Dawn and dusk, still humid air near water	Dusk and after dark, plus shaded daytime

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What No-See-Ums Actually Are

Despite the name, no-see-ums are not mysterious. They are biting midges — tiny two-winged flies in the family Ceratopogonidae, most often the genus Culicoides. In Ontario you might also hear them called punkies, sand flies, or moose flies. At just 1 to 3 mm long, an adult is roughly a quarter the size of a mosquito, which is exactly why you feel the bite before you ever spot the culprit.

As with mosquitoes, only the female bites. She needs a blood meal to develop her eggs, and she finds you using the same cues a mosquito does — the carbon dioxide in your breath, body heat, and skin odours. Males feed on nectar and don’t bite at all. The larvae develop in consistently moist places: the muddy margins of ponds and marshes, soggy leaf litter, wet compost, damp mulch, tree holes, and saturated lawn edges. Anywhere the ground stays wet is potential no-see-um habitat.

Why Regular Screens Don’t Stop Them

This is the single most frustrating thing about biting midges: your windows can be shut, your porch screened in, and they still get to you. Standard insect screening is woven with mesh openings of roughly 1.1 to 1.5 mm — plenty fine for houseflies and mosquitoes, but a wide-open door for a 1 mm midge. They simply fly through the holes.

The fix is “no-see-um mesh,” a finer weave (often labelled around 20x20 strands per inch, with openings near 0.6 mm) sold specifically for porches, gazebos, tents, and RV windows. The catch is airflow: tighter mesh cuts the breeze, so a screened porch can feel stuffier. A practical Ontario compromise is fine mesh on the most-used openings plus a fan on the patio — biting midges are weak fliers, and even a modest breeze grounds them.

When and Where They Swarm in Ontario

Biting midges are a late-spring-through-summer problem in Ontario, generally worst from late May into August. Two conditions drive the heaviest swarms:

Time of day. Dawn and dusk are peak feeding windows. A calm, warm, humid evening on the deck is prime no-see-um time.
Proximity to water and stillness. Because they are feeble fliers, midges concentrate where the air is calm near their wet breeding grounds — lakeshores, ponds, marshes, ravines, drainage ditches, and cottage country. The moment a breeze picks up, they largely disappear.

This is why the cottage dock at sunset can be miserable while a windy afternoon at the same spot is bite-free, and why the nuisance often overlaps with early-summer black fly season. Suburban GTA yards near creeks, storm ponds, and low wet corners get their share too, not just cottages.

Preventing No-See-Um Bites

Because midges are so small and feed in clusters, a layered defence works far better than any single trick:

Time it. Avoid still, humid dawn and dusk hours near water when you can, or move to a breezier spot.
Use a fan. On a patio or dock, a simple oscillating fan is one of the most effective tools there is — midges can’t fly against moving air.
Cover up. Long, light-coloured sleeves and pants at dusk reduce exposed skin, especially at the ankles and wrists where midges love to feed.
Apply a proven repellent. Health Canada registered products with DEET or picaridin (icaridin) work against biting midges; oil of lemon eucalyptus is a plant-based option. Cover ankles, wrists, and the hairline well.
Treat clothing and gear. Permethrin-treated fabric adds a strong barrier for repeat exposure at the cottage or on trails.

Not sure which skin repellent to reach for? Our guide on picaridin vs DEET in Canada breaks down which active fits which situation. To shop current options:

Check picaridin repellent on Amazon.ca →Check a Thermacell repeller →

A Thermacell-style area repeller can also help create a small protected zone on a still patio, working alongside a fan rather than replacing it.

Treating Bites You Already Have

No-see-um bites itch out of proportion to their size, and scratching only invites infection. To calm them: wash the area with soap and water, apply a cold compress to reduce swelling, and use an over-the-counter antihistamine or a hydrocortisone/anti-itch cream to control the reaction. Keep fingernails off the welts. If a bite becomes very swollen, spreads, oozes, or shows signs of infection, contact a healthcare provider — some people react strongly to midge saliva.

Reducing No-See-Ums Around Your Yard

You can’t drain a whole marsh, but you can make your own property less hospitable and thin out the adults that rest there:

Fix drainage. Eliminate spots where water pools after rain — the saturated ground is where larvae develop.
Clear damp organic matter. Rake out soggy leaf litter, thin overly wet mulch beds, and keep gutters and low corners draining freely.
Keep it moving. Permanent fans over seating areas keep the adults off you all evening.
Barrier treatment for heavy pressure. Adult midges (like mosquitoes) shelter by day in shaded, humid vegetation. A professional barrier spray applied to those resting zones — shaded shrubs, damp edges, fence lines — reduces the biting population that reaches your patio.

For most Ontario homeowners the realistic goal isn’t total eradication — it’s getting your yard usable again at the exact hours you want to be outside. A combination of drainage, airflow, personal repellent, and a barrier treatment on the shaded resting sites does that better than any one measure alone.

No-See-Ums & Biting Midges in Ontario: Bites, Screens & Control

What are no-see-ums and why can’t you see them?

No-See-Um Bites vs Mosquito Bites: How to Tell Them Apart