Why do I have mosquitoes in my home even when the windows are closed?
Camille VidalAre you finding mosquitoes inside your home even though your windows are closed? You’re not alone: it’s one of the most common questions asked in the UK between May and October. In most cases, they get in through invisible access points (vents, seals, doors) or they breed very close to your home. After more than 15,000 homes equipped, here’s what we see most often with our customers, and the solutions that genuinely work.
Mosquitoes indoors with windows closed: the 8 most common causes
1. The front door or patio door: entry point #1
This is the cause we see most often. You open the door for a few seconds (coming and going, deliveries, taking out the bins) and several mosquitoes take advantage. Drawn in by the CO₂ and heat escaping, they slip in instantly. Once indoors, they hide (curtains, under furniture, ceiling corners) and only come back out in the evening or at night.
MOSKERA tip: that’s exactly why a magnetic door fly screen is the first protection to put in place. It closes automatically after every pass-through.
2. Air vents, mechanical ventilation and ventilation grilles
Mosquitoes can come in through air vents and ventilation grilles, especially if the insect mesh is missing, damaged or too wide (above 1.2 mm). This is common in older properties or buildings with natural ventilation.
3. Roller shutter boxes (invisible gaps)
Roller shutter boxes are often overlooked. Yet the corners and slat passages frequently leave tiny gaps. You may not see them with the naked eye, but they’re more than enough for a mosquito.
4. Worn seals, cracks and cable openings
Worn window seals, skirting boards coming away, service holes (fibre, air conditioning, electrical cables), micro-cracks near a window… These are discreet openings but more than sufficient. A seal that no longer sits flush over just 2 cm is an open door for insects.
5. Communal areas, landing and bin room (in apartment buildings)
In a flat, mosquitoes can come from the landing, stairwells, the bin room or cellars. They follow warm air and CO₂ flows and enter as soon as your door opens. If communal areas are damp or poorly ventilated, the issue is often recurring.
6. Standing water nearby (balcony, garden, gutter)
Mosquitoes lay eggs in standing water: plant saucers, a forgotten bucket, a rainwater collector without a lid, a blocked gutter, children’s toys filled with rainwater… It only takes a few millilitres of still water for 7 days for a breeding site to establish. If that site is close to your openings, you’ll see regular arrivals.
7. Mosquitoes already inside
Sometimes the cause is simpler than you think: they got in the day before (or earlier) and stay discreet during the day. Some species can also lay eggs in a damp area indoors (shower tray, utility room, under the sink). Result: it feels like they appear “out of nowhere”.
8. The window itself: weep holes, trickle vents and tired seals
A closed window is not a sealed window, and this is how bugs get in through a window that looks shut. Aluminium and uPVC frames have weep holes, the small drainage slots along the bottom of the frame that open straight to the outside. Many windows also carry a trickle vent in the top rail, and older frames rely on seals that flatten with age: a gap of two or three millimetres along the sash is invisible to you and wide open to a mosquito or a midge.
The fix is not to block any of this, weep holes and vents are there to drain water and move air. Cover the opening with fine insect mesh instead, or fit a screen over the whole window frame, so drainage, airflow and protection keep working together.
Key takeaway: if you see mosquitoes even though the windows are closed, the cause is almost always an alternative entry point (doors, vents, micro-gaps) combined with a nearby breeding site.
How to find the mosquitoes’ entry point (checklist)
Go through each point to identify where they’re coming from:
- Light test (in the evening): switch off all indoor lights. With a torch, inspect the edges of windows, doors and vents: any visible gap = likely entry.
- Under doors: run your hand under the front door and patio doors. If you feel a draught, mosquitoes can get through too.
- Vents and ventilation: check for a fine, intact mesh on every vent.
- Roller shutter box: inspect corners and slat passages with a torch.
- Standing water: check your balcony, garden and terrace. Empty any still water (saucers, buckets, gutters, drains).
- Targeted observation: if mosquitoes mainly appear in the evening near a specific door or window, the entry point is very close.
Effective solutions against mosquitoes indoors (immediate + long-term)
Immediate solutions (for tonight)
- Reduce light attraction: close shutters and curtains before dusk. Avoid bright lights near open doors and windows.
- Remove all standing water: even a saucer with a small amount of water can be a breeding site.
- Spot and remove: mosquitoes often rest on walls, curtains and ceilings during the day. Check these areas in late afternoon.
- Directed fan: mosquitoes struggle in airflow. A fan aimed at your bed or sofa keeps them away effectively.
Long-term solutions to stop mosquitoes coming indoors
- Seal entry points: replace door and window seals, block gaps under doors (adhesive draught excluder), seal cable openings.
- Secure ventilation: fit or replace insect mesh on ventilation grilles and outlets.
- Install a fly screen on main openings: it’s the simplest, most durable solution. A magnetic fly screen lets you air your home freely without letting in a single mosquito, and it installs in 10 minutes with no drilling.
If your main issue is “mosquitoes indoors at night” or “mosquitoes despite closed windows”, the priority is almost always the same: secure doors and large openings first.
Frequently asked questions
Is it possible to have mosquitoes in winter with the windows closed?
Yes. Some mosquitoes survive in sheltered areas (garage, cellar, communal areas) and take advantage of brief openings to get inside. Indoor warmth can encourage their presence even in mid-winter.
Why do I mainly get mosquitoes in the bedroom?
The bedroom is where you spend the most time still. You breathe (CO₂), the temperature is stable and darkness suits them. They get in when a door or window opens, hide during the day and come out at night when you sleep.
Can mosquitoes come through ventilation grilles?
Yes, if there’s no insect mesh, if it’s damaged, or if the openings are larger than 1.2 mm. Check every grille in your home and replace any that are defective.
What’s the most effective solution against mosquitoes indoors?
The most effective long-term approach is to block entry points. Installing a magnetic fly screen on doors and windows lets you ventilate without letting mosquitoes in. It’s the solution chosen by over 10,000 MOSKERA-equipped households.
How long does it take to install a magnetic fly screen?
Around 10 minutes, with no drilling or tools. MOSKERA fly screens attach via adhesive or magnetic strips directly to the door or window frame. They’re just as easy to remove, without damaging surfaces.
Can bugs get through closed windows or an intact fly screen?
Through a truly sealed window, no. But most closed windows still breathe through weep holes, trickle vents and ageing seals, and bugs simply follow that airflow. Through a fly screen, only if the mesh is torn, coarser than the insect, or badly fitted at the edges: an intact fine mesh stops mosquitoes, flies and midges. So inspect the edges and the weave rather than the middle of the screen.
Protect your openings with a MOSKERA magnetic fly screen
More than 10,000 households have chosen MOSKERA for peaceful, mosquito-free nights. Install in 10 minutes, no drilling, made to measure. Choose the model suited to your opening:
Door fly screen
Front door, patio door, balcony door.
From $59.99
- Automatic magnetic closure
- Standard up to 120 × 210 cm & made to measure
- No drilling · 10-minute install
Window fly screen
Standard window, tilt-and-turn, top-hung.
From $59.99
- Removable magnetic fixing (or velcro on request)
- Made to measure
- Black or white · No drilling
Large-size fly screen
Sliding doors, large glazed openings, pergola.
From $199.99
- Multi-panel magnetic system
- Made to measure for large openings
- No drilling · Easy installation
✓ Made to measure · ✓ No drilling · ✓ 500+ verified reviews · ✓ Fast delivery
How they get into an Australian house
Australian construction leaves a set of openings that simply do not exist in a European house, and they explain most of the cases where someone is certain everything was shut.
Under the floor
Any house on stumps or piers has a ventilated subfloor, and any brick veneer house has weep holes along the base course. Both are meant to be there and neither should be blocked. The subfloor is cool, shaded and humid, which makes it the preferred daytime resting place for adults, and from there they work their way up through gaps around pipe penetrations, at the edge of floorboards, and behind a kitchen or bathroom cabinet where the plumbing comes through.
Down from the roof space
Roof spaces here are ventilated by design, through eave vents, gable vents or a whirlybird. Recessed downlights, exhaust fans and the gap around a ceiling hatch all connect that space to the room below. It is a common path in a single storey house and it explains bites in a bedroom whose window has not been opened for weeks.
The openings that are not quite closed
- Louvre windows, which do not seal when closed and are never meant to.
- The gap at the bottom of a sliding door track, especially on an older aluminium slider.
- An unsealed pet door, or one whose flap has warped in the sun.
- Range hood and bathroom exhaust ducting where the external flap has stopped closing.
- Split system pipework where it passes through the wall and the sleeve was never sealed.
And the simplest explanation of all
In most Australian houses the sliding door onto the deck was open at dusk, even briefly, and that is when they came in. Everything above is worth checking, but if the biting starts in the evening and continues after the house is shut, the insects were almost certainly already inside before it was. Screening that one opening is what changes it.
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Read next : Fly screen without drilling: the complete guide to fitting one without damage
How do mosquitoes get in when the windows are closed?
Even with every window closed, a home is never completely airtight. Mosquitoes are only 3 to 6 mm long, a gap of just a few millimetres is enough. They’re attracted by the CO₂ you exhale, body heat and certain skin odours. They detect these signals from several metres away and follow the trail to the smallest opening.
The most common entry points we see with our customers: doors (even when opened for a few seconds), air vents and mechanical ventilation, roller shutter boxes, worn seals and cable pass-throughs. Sometimes, mosquitoes were already inside without you realising.