Why mosquitoes are still biting in France in October and how to get rid of them

Mosquitoes are still biting in France despite the arrival of autumn, with some people wondering why they seem more numerous now than during the summer heatwave.

The answer is partly down to the lack of rainfall during the hottest months.

Mosquitoes need water to reproduce. Females lay their eggs in or around small areas of stagnant water, where the larvae develop.

During the long periods of extreme heat and dry weather this summer, many of these potential breeding sites dried up. This reduced the amount of water available for mosquito larvae to develop and helped bring mosquito numbers down.

The return of rain though can quickly change the situation as tiger mosquitoes are very well adapted to these conditions. 

Their eggs can survive for weeks or even months in dry conditions, waiting for water to return. When rainwater reaches the eggs, they can hatch and the mosquito life cycle starts again.

Another reason for their low numbers during the heatwave was that the extreme heat itself also affected them.

Mosquitoes are cold-blooded insects and their development is influenced by temperature. Warm conditions usually speed up their life cycle, but very high temperatures can become harmful.

At temperatures above around 35C, mosquitoes can become less active, lose water more quickly and die sooner. During the hottest parts of the day, they may also seek shelter in cooler, shaded places.

Meanwhile, autumn can provide conditions that are much more favourable for mosquitoes. There is once again enough water for breeding, while temperatures can remain warm enough for them to develop.

This is why precautions are still important, especially against the tiger mosquito, which is now widely established across mainland France. The species can transmit viruses responsible for diseases including dengue, chikungunya and Zika.

How to keep them away 

The best way to reduce mosquito numbers is to stop them from breeding in the first place.

“The best mosquito is the one that is not there,” Grégory L’Ambert, head of the preventive tiger mosquito control and public health unit at EID Méditerranée, previously told The Connexion. 

Mosquitoes need water to develop, so removing stagnant water around the home can make a significant difference.

“It is not about draining a marsh or a river,” Mr L’Ambert said. “The mosquitoes that bite us are often developing in collections of water around our homes: watering cans, rain collectors etc.”

This means regularly checking plant saucers, buckets, gutters and other outdoor containers, particularly after rainfall.

Rainwater collectors can also become breeding sites if they are not properly covered. Pet water bowls should also be emptied and refilled regularly, while fallen fruit and garden debris should be cleared away.

Then, if mosquitoes are already around, one simple solution is to use a fan.

“For mosquitoes, especially tiger mosquitoes, it can be very effective because they do not fly very well. If you have one or two reasonably-sized fans blowing air towards your legs or your body, the mosquito will have difficulty reaching you. After a while, it gives up and goes elsewhere,” Mr L’Ambert said.

Other measures can also reduce the risk of being bitten, including wearing loose-fitting, light-coloured clothing, installing mosquito nets and using a repellent.

In order for repellents to work, they need to contain one of three active ingredients: DEET, IR3535 or icaridin.

What about citronella?

Citronella candles, plants and essential oils are often considered as natural ways of keeping mosquitoes away, but Mr L’Ambert said their effectiveness is often overstated.

He said studies showing an effect from citronella used much higher quantities than would normally be found around a garden table.

“A small pot of citronella on a table will not stop mosquitoes from coming to bite you,” he said.

Mosquito traps should also be positioned carefully. Placing one next to a terrace or dining area could actually attract mosquitoes towards the people sitting there.

When are they likely to go? 

Mosquitoes become much less active as temperatures fall, with biting and flying activity dropping significantly below about 10-15C.

However, the exact temperature threshold varies depending on the species.