Still getting bitten in October? Where house mosquitoes hide, and what to do

The windows have been closed for weeks, yet something is still buzzing by the pillow. The common house mosquito doesn’t simply disappear in autumn. The European Centre for Disease Prevention and Control says mated females can survive winter in sheltered places protected from deep frost, including cellars, caves, bunkers and burrows.

This October, take a moment to look around the house and garden. Some mosquitoes are preparing to spend winter out of sight, while others can remain active indoors. And any standing water left around the property may provide breeding sites, even while temperatures remain mild.

Two house mosquitoes, two winter strategies

The common house mosquito, Culex pipiens, comes in different forms that behave quite differently.

The pipiens form normally enters winter dormancy, or diapause. Only mated females are active over winter. Research shows that females preparing for diapause largely stop seeking blood meals and switch to feeding on plant sugars to build up the fat reserves they need for winter. That means a mosquito actively biting you indoors in autumn may not be one of those already settled down for winter.

The molestus form is different. It has a stronger preference for humans, often lives around buildings, and does not have an obligatory winter diapause. It can continue reproducing during winter in warm, dark places where water is available, including flooded cellars.

Recent research from Wageningen University also found that molestus mosquitoes were more common in highly urbanised areas. These mosquitoes were more likely to live in homes with flooded crawl spaces, suggesting that these spaces can contribute to winter mosquito problems.

Researchers found them in 44% of cellars

A German study gives an idea of just how useful buildings can be as winter shelters.

Researchers inspected 149 structures in north-west Germany during two winters. Mosquitoes were found in 44% of the cellars and 33% of above-ground structures, with Culex pipiens pipiens the most abundant mosquito in the cellars.

Interestingly, warmer wasn’t necessarily better. In a follow-up experiment, higher average temperatures between 5°C and 16°C were associated with greater winter mortality. A cool but frost-free cellar can therefore be a perfectly suitable hiding place.

The autumn job that matters most: look for water

You don’t need to hunt individual mosquitoes around the garden. Start with water.

Experts advise checking regularly for standing water because mosquitoes lay their eggs in it. Empty plant saucers and buckets, remove water from covers and tarpaulins, make sure gutters drain properly and keep rain barrels covered. If there is water underneath the house, check whether the cause can be fixed rather than simply leaving it through winter.

A healthy garden pond is slightly different. Water beetles, dragonfly larvae, fish, and frogs can feed on mosquito larvae, while moving water from a fountain also makes conditions less attractive.

Inside, check gaps around pipes and cables leading up from a crawl space or cellar. Screens can also remain useful while mosquitoes are still active, even though most people pack them away when summer ends.

And what about mosquito bites now?

In the Netherlands, there is an extra reason in 2026 to avoid unnecessary bites. RIVM recently reported that West Nile virus had been detected in people, horses, birds, and common house mosquitoes at several locations this year. Most infections cause no symptoms, but the common house mosquito can transmit the virus after feeding on an infected bird.

Don't panic over an October mosquito, but clearing standing water, checking damp spaces, and blocking obvious routes indoors are sensible jobs to do now, and may leave fewer places for mosquitoes to breed or spend the winter before spring returns.