What Are No-See-Ums? Biting Midge Bites, Screens & Control in Ontario

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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.

Mesh grade is also the spec to check before buying any outdoor enclosure, because most models ship with standard netting that midges walk straight through. If you are shopping for a deck structure, our screened gazebo buyer’s guide explains how the holes-per-square-inch rating separates midge-proof models from mosquito-only ones.

You rarely need to redo the whole house. Rescreening the porch door and the two or three windows you actually sit beside covers most of the problem.

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:

1. Time it. Avoid still, humid dawn and dusk hours near water when you can, or move to a breezier spot.
2. 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.
3. Cover up. Long, light-coloured sleeves and pants at dusk reduce exposed skin, especially at the ankles and wrists where midges love to feed.
4. Apply a proven repellent. Products with DEET or picaridin (icaridin) and a PCP registration number on the label work against biting midges; oil of lemon eucalyptus is a plant-based option. Cover ankles, wrists, and the hairline well.
5. 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:

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.

If you are still not certain the welts you are treating came from a midge at all, our closer look at what no-see-um bites look like and how long they last follows a bite through its stages — the burning pinprick, the red dot hours later, the hard welt still itching days on — which is the detail that usually settles the question, since the insect itself is long gone by the time you look.

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.

Related Reading

• Picaridin vs DEET in Canada — Which Repellent to Choose
• Black Flies in Ontario — When They Come Out
• Mosquito Season in the GTA — When Does It Start?
• Thermacell Canada — Where to Buy + Do They Work
• BuzzSkito Professional Mosquito Control Service

Repellent guidance reflects Health Canada’s pest-management information. Always follow the product label. See Health Canada — Pesticides and Pest Management.

Frequently Asked Questions