---
title: "Can No-See-Ums Bite Through Window Screens?"
description: "# Can No-See-Ums Bite Through Window Screens? **Yes — no-see-ums can easily pass through standard window screens.** Most U.S. homes use 18×16 mesh, whose openings are wide enough for biting midges to walk or fly straight through. Upgrading to 20×20…"
url: "https://stinghelp.com/docs/can-no-see-ums-bite-through-window-screens/"
updated: "2026-10-21"
---

# Can No-See-Ums Bite Through Window Screens?

# Can No-See-Ums Bite Through Window Screens?

**Yes — no-see-ums can easily pass through standard window screens.** Most U.S. homes use 18×16 mesh, whose openings are wide enough for biting midges to walk or fly straight through. Upgrading to 20×20 (or finer) "no-see-um mesh," plus sealing gaps and tears, is the reliable way to keep them out.

![Tiny biting midge resting on a fingertip for size comparison](https://stinghelp.com/wp-content/uploads/2026/10/can-no-see-ums-bite-through-window-screens-2.webp)

## The Short Answer: Yes, They Can Get Through Standard Screens

If you have ever woken up covered in itchy red welts despite sleeping with the windows open only behind intact screens, no-see-ums are the likely culprit. These biting midges — members of the fly family Ceratopogonidae, also called sand flies, punkies, or midgies — are so small that standard insect screening was never designed to stop them.

Standard residential window screen in the United States is woven at roughly 18 strands per inch in one direction and 16 (or 14) in the other. That weave keeps out mosquitoes, house flies, and moths without trouble. But pest-control professionals note that insects smaller than about 1/20 of an inch — including no-see-ums, gnats, and thrips — pass through those openings with ease. The screen looks fine, the frame looks fine, and yet the midges are inside anyway. This is the single most misunderstood part of no-see-um control: **the screen is not broken; it is simply the wrong mesh for this pest.**

This guide explains how mesh sizes compare, which screen to buy, how to install or re-screen windows yourself, how to seal the other entry points around your home, and what to do when bites happen anyway.

### What Mesh Size Actually Means

Mesh density is written as a ratio — for example, 18×16 — that counts the number of strands per linear inch in each direction. A higher number means more strands, a tighter weave, and smaller openings. But the number alone does not tell the whole story: the thickness of the wire or yarn also affects the actual opening size. Two screens labeled 20×20 from different manufacturers can have slightly different opening sizes depending on the filament diameter.

What matters for you is the effective opening size relative to the insect you are trying to stop. For no-see-ums, pest-control sources consistently recommend 20×20 mesh or finer as the minimum upgrade, with some manufacturers offering 20×30 weaves marketed specifically as no-see-um screening.

### How Big Are No-See-Ums Compared to Mesh Openings?

No-see-ums earned their name honestly: adults are typically about 1–3 millimeters long, barely visible as specks to the naked eye, and greyish or light brown so they blend into skin and shadow. Standard 18×16 mesh has openings on the order of 1.1–1.4 millimeters, depending on wire thickness — roughly the same size as, or slightly larger than, the midge's body. Worse, midges are flexible and persistent; they do not need a comfortable doorway, just a gap their body can compress through.

By comparison, mosquitoes measure roughly 3–6 millimeters, which is why the same screen that stops mosquitoes is nearly invisible as a barrier to a midge. Think of it this way: to a mosquito, your screen is a wall; to a no-see-um, it is a ladder with convenient footholds.

![Close-up of fine window screen mesh seen against bright daylight](https://stinghelp.com/wp-content/uploads/2026/10/can-no-see-ums-bite-through-window-screens-1.webp)

## Window Screen Mesh Sizes Compared

The table below summarizes the common mesh choices for residential windows and how they perform against the pests homeowners care about. Figures are typical values reported by screen manufacturers and pest-control sources; exact opening sizes vary with filament thickness, so confirm the effective opening with the product specifications before buying.

| Mesh | Typical Opening Size | Stops | No-See-Um Protection? | Airflow & Visibility | Best For |
| --- | --- | --- | --- | --- | --- |
| 18×14 | ~1.3 mm | Mosquitoes, flies, moths, wasps | No — midges pass through freely | Excellent airflow, clear view | General use in areas without tiny biting insects |
| 18×16 (standard U.S.) | ~1.1–1.3 mm | Mosquitoes, flies, moths, most beetles | No — no-see-ums slip through | Very good airflow, clear view | Most homes; the default for new windows |
| 20×20 (no-see-um mesh) | ~0.85–1.0 mm | Midges, gnats, thrips, plus everything above | Yes — the standard upgrade for biting midges | Good airflow, slightly dimmer view | Coastal areas, marshes, lakefront, wooded lots |
| 20×30 (extra-fine) | ~0.6–0.8 mm | Nearly all small flying insects | Yes — maximum physical barrier | Reduced airflow and visibility | Heavy midge pressure, screened porches, sunrooms |
| Solar / sun-control screen | Varies (dense weave) | Depends on weave; often blocks small insects incidentally | Often yes, but verify opening size | Noticeably reduced light and airflow | Hot climates where heat reduction matters too |

### Reading the Table: Which Mesh for Which Pest

If your complaint is mosquitoes and flies, standard 18×16 is enough and gives you the best breeze and view. If your complaint is no-see-ums, gnats, or sand flies, you need the 20×20 row or finer — there is no shortcut around physics. The 20×30 row is worth considering for sleeping porches and bedrooms if you are highly reactive to bites, but expect to trade some airflow and daylight for it.

One caution: denser mesh also clogs faster with pollen, dust, and salt spray, so fine screens need cleaning a few times per season to keep air moving. A dirty 20×20 can move less air than a clean 18×16 — and still block midges either way.

## Why No-See-Ums Slip Through (But Mosquitoes Usually Don't)

Size is the obvious reason, but it is not the whole reason. Three traits of biting midges make them exceptionally good at getting indoors:

### Tiny Bodies, Weak Wings

Adult no-see-ums are weak flyers. On the face of it, that sounds like good news — and it is, outdoors, where a fan or a light breeze of just a few miles per hour can create a zone they cannot fly into. Indoors, though, weak flying means they drift: they ride air currents through open doors, follow you inside when you enter, and settle out of moving air onto skin, bedding, and walls. They are most active at dawn and dusk, exactly when people open windows to cool the house.

### They Crawl, Not Just Fly

No-see-ums do not need an open window. They crawl through the weave of loose-knit clothing (a standard cotton T-shirt's knit is open enough for them), along window tracks, under doors, and through the mesh itself. Many indoor bite complaints happen in homes where every screen looks perfect — because the midges came in through the screen rather than around it.

### Screens Are Only Half the Story: Gaps and Tears

Even a brand-new 20×20 screen fails if the frame has a gap. Common bypass routes include shrunken or missing spline (the rubber cord that holds the mesh in the frame), bent frames that do not sit flush in the track, torn mesh from pets or storms, missing screens on attic or foundation vents, and the inch-wide gap at the meeting rail of double-hung windows. Before spending money on finer mesh, fix the gaps — otherwise you will upgrade the mesh and still wake up bitten.

![Person re-screening a window frame with new fine mesh](https://stinghelp.com/wp-content/uploads/2026/10/can-no-see-ums-bite-through-window-screens-3.webp)

## How to Upgrade Your Screens to Stop No-See-Ums

Re-screening a window with finer mesh is a straightforward do-it-yourself project. A single window typically takes 20–30 minutes once you have the materials, and the cost is a fraction of custom replacement screens.

### Materials and Tools Checklist

- No-see-um screen mesh, 20×20 or finer (fiberglass is cheapest and easiest; aluminum and polyester/stainless options are tougher and longer-lived)
- Spline (rubber cord) in the diameter that matches your frame's groove — bring a piece of the old spline to the store
- Spline roller tool (the concave wheel presses the spline into the groove)
- Utility knife with a fresh blade and a flathead screwdriver or awl
- Tape measure; order or cut mesh a couple of inches larger than the frame on every side
- Optional: new frame corners and a hacksaw if frames are bent or corroded

### Step-by-Step Re-Screening

1. **Remove the frame.** Lift the screen out of the window track. On most windows, pull the spring clips or lift the frame up and out toward you.
2. **Strip the old mesh.** Pry up one end of the spline with a screwdriver and pull it out of the groove all the way around. Lift off the old screen and wipe the groove clean of dirt and old rubber.
3. **Lay the new mesh.** Place the frame flat, lay the 20×20 mesh over it with a couple of inches of overhang on every side, and keep the weave square — crooked mesh will not tension evenly.
4. **Roll in the spline.** Starting at a corner, press the spline into the groove over the mesh with the spline roller, working around the frame. Keep gentle, even tension on the mesh as you go; pull it taut but do not stretch it.
5. **Trim the excess.** Run a sharp utility knife along the outside of the groove to trim the mesh flush. One smooth pass beats several ragged ones.
6. **Reinstall and check.** Seat the frame back in the track. Check all four edges for gaps — a credit card should not slide easily between the frame and the track. Hold the screen up to daylight and look for wrinkles or loose spots.
7. **Do the high-priority windows first.** Bedrooms and any window you open at dawn or dusk matter most. You do not have to re-screen the whole house in one weekend.

If frames are bent, corroded, or the wrong size, pre-made replacement screens ordered to your window measurements are worth the extra cost — a perfect-fitting frame with fine mesh beats a warped frame with perfect mesh.

## Sealing the Rest of the House: Gap Checklist

Fine mesh is the main fix, but midges exploit every other opening too. Work through this checklist room by room, ideally before midge season peaks in your area.

- **Doors:** install or replace weatherstripping and door sweeps; check that the sweep brushes the threshold along its full width. Keep doors closed at dusk.
- **Window tracks:** vacuum out the tracks and check for gaps where the sash meets the frame, especially on double-hung windows.
- **Vents:** cover attic, soffit, and foundation vents with fine-mesh screening; bathroom and dryer vents should have intact flappers.
- **Utility penetrations:** seal gaps where pipes, cables, and AC lines enter the house with caulk or expanding foam.
- **Chimneys and fireplaces:** a chimney cap with fine mesh keeps out insects as well as animals.
- **Porches and lanais:** if you have a screened porch, re-screen it with 20×20 or finer — a porch screened in standard mesh is a midge sanctuary, not a refuge.
- **Pet doors:** magnetic-sealing pet doors let in fewer insects than loose flaps; consider closing them at peak midge hours.

### A Note on Air Conditioning

No-see-ums follow warm, humid, still air. Running air conditioning during peak season does three things at once: it lets you keep windows closed, it dries indoor air, and the supply registers create air movement midges dislike. If you prefer open windows, restrict them to the middle of the day, when midges are least active, and close them an hour before sunset.

## Indoor Prevention Checklist

Even with upgraded screens, a few midges will occasionally hitch a ride inside on clothing, pets, or groceries. These habits keep indoor encounters rare and bite counts low.

- Keep bedroom windows closed from an hour before sunset to an hour after sunrise during midge season.
- Run a ceiling fan or a portable fan in the bedroom at night — moving air is one of the most reliable midge deterrents.
- Shake out clothing and check pets at the door during peak hours.
- Use yellow or warm-white bulbs on porches; bright white light near open doors attracts night-flying insects.
- Fix indoor water issues — midges breed in moist soil and organic matter, so overwatered houseplants and damp areas under sinks can theoretically support them. Let plant soil dry between waterings.
- Consider a fine-mesh bed net if you sleep with windows open in a high-pressure area; tuck it under the mattress so there are no gaps.

### Sleeping Areas Deserve Priority

Most no-see-um bite complaints involve bites discovered in the morning — clusters of small, intensely itchy welts on ankles, wrists, the neck, or any skin left uncovered overnight. Midges feed quietly and painlessly at first; the itch arrives hours later. Protecting the bedroom — fine mesh on its windows, a fan running, sheets rather than bare skin — prevents the majority of indoor bites.

## Outdoor Prevention Checklist

You cannot screen the outdoors, but you can make your yard and your habits less inviting to biting midges.

- **Time your outings.** Midges are most aggressive at dawn and dusk and on calm, humid, overcast days. Plan yard work and outdoor meals for midday or breezy conditions.
- **Use repellent as directed.** Products containing DEET or picaridin are the most consistently effective against biting midges; apply to exposed skin according to the label. Oil of lemon eucalyptus is a plant-based option recognized by public-health agencies for repelling biting insects.
- **Cover up with tight weaves.** Long sleeves and pants in tightly woven fabric block midges far better than loose knits, which they can crawl through. Tuck pants into socks in heavy-pressure areas.
- **Create airflow.** A strong patio fan aimed at seating areas disrupts their weak flight and dramatically cuts landing rates.
- **Reduce breeding habitat.** Midges develop in moist soil, mud, marsh edges, and decaying organic matter. Improve drainage, avoid overwatering, and clear leaf litter and mulch buildup near patios and doorways.
- **Trim vegetation near the house.** Dense, damp plantings against walls give adult midges daytime resting spots close to your doors and windows.

For related outdoor strategies, see our [outdoor bite prevention checklist](https://stinghelp.com/docs/outdoor-bite-prevention-checklist/).

## No-See-Um Bites: What They Look Like and How to Care for Them

No-see-um bites typically appear as small, red, intensely itchy welts, often in clusters or lines where clothing was loose or skin was exposed. The bite itself is usually painless — many people feel nothing until the itching starts several hours later. For most people, the welts fade within a few days to a week, though scratching can prolong healing and break the skin.

### Cleaning and Soothing Bites

- Wash the area gently with soap and water as soon as you notice the bites.
- Apply a cool compress or a cool, damp cloth for short periods to ease itching and swelling.
- Use an over-the-counter anti-itch product as directed on the label; avoid scratching, which can break the skin and invite infection.
- Keep fingernails short and the area clean while it heals.
- Watch the bites over the next 24–72 hours — most improve steadily day by day.

### Warning Signs That Need Medical Attention

**Seek prompt medical care if you notice any of the following after bites or stings:**

- Signs of a severe allergic reaction: trouble breathing, wheezing, swelling of the lips, tongue, or throat, dizziness, or fainting — call 911 immediately.
- Spreading redness, increasing warmth, or red streaks extending from a bite, which can indicate a skin infection.
- Pus, increasing pain, or swelling that worsens after the first 24–48 hours instead of improving.
- Fever, chills, or feeling generally unwell after multiple bites.
- Bites near the eyes or inside the mouth or nose, or a very large number of bites at once.
- Any reaction that worries you, especially in young children, older adults, or anyone with a known insect allergy — when in doubt, get checked.

For a broader overview of concerning symptoms, see [severe reaction and infection warning signs](https://stinghelp.com/docs/bite-sting-warning-signs/).

## Frequently Asked Questions

### Can no-see-ums bite through clothing?

They do not really bite *through* fabric so much as crawl *through* it. The weave of a loose-knit cotton shirt or thin socks has openings large enough for a 1–3 mm midge to wriggle past and reach the skin underneath. Tightly woven long sleeves and pants are far more protective. If you find bites under clothing, that is the usual explanation.

### Will a bug zapper or citronella candle keep no-see-ums away?

Evidence for both is weak against biting midges. Bug zappers mostly kill moths and beetles attracted to ultraviolet light, not the midges seeking you out. Citronella candles provide only a very small zone of mild effect outdoors and are easily overwhelmed by a breeze. Fans, repellents used as directed, and fine mesh are the measures with the best track record.

### How small an opening can a no-see-um fit through?

Adults are roughly 1–3 millimeters long, and like many small flies they can compress their bodies to pass through gaps slightly smaller than their body width. As a rule of thumb, any opening around a millimeter or larger is passable. That is why 20×20 mesh — with openings under a millimeter — is the recommended minimum, and why even a warped screen frame with a hairline gap can let them in.

### Are no-see-um bites dangerous?

For most people, no-see-um bites are a painful nuisance rather than a medical emergency: intense itching and welts that resolve within days. The main risks are secondary skin infection from scratching and, rarely, significant allergic reactions in sensitive individuals. In some regions, biting midges can carry animal diseases, but they are not considered major vectors of human disease in the United States. Seek care if you notice the warning signs listed above.

### Do no-see-ums live inside houses?

They do not typically establish breeding populations indoors the way fruit flies or drain flies do — their larvae need moist soil or organic matter, which houses usually lack. Indoor midges are almost always intruders from outside that came through screens, gaps, or open doors, or that were carried in on clothing or pets. That is good news: fix the entry points and the indoor problem usually resolves on its own.

Medical disclaimer: This article is for general information only and is not medical advice. It does not replace professional diagnosis or treatment. If you are concerned about a bite or sting, contact a clinician, urgent-care clinic, or your local poison-control center. Call 911 immediately for any emergency, including trouble breathing, facial or throat swelling, dizziness, or fainting.