Mosquito season is getting longer in France as milder and wetter conditions encourage the insects to remain active well into the autumn across, say scientists.
This longer period of activity can be dangerous as it can increase the risk of the transmission of viruses such as dengue fever, chikungunya and zika by tiger mosquitoes, and West Nile and Usutu by the common mosquito.
These viruses can be imported to mainland France by travellers from tropical zones where epidemics are rife.
Mosquitoes can act as “vectors” for the viruses, biting an infected person and passing the disease on to the next person it bites.
Guillaume Lacour, a medical entomologist at Altopictus, a company based in Occitanie that specialises in monitoring and removing tiger mosquitoes, told The Connexion it is becoming increasingly normal for the insect to be active at this time of year.
He said its biting activity generally ceases now around mid-November, depending on the weather.
“The Aedes albopictus (Asian tiger mosquito) vector season is not over in the south of France, as demonstrated by this stable activity in Occitanie,” he said.
“It is common to have active Asian tiger mosquitoes until mid-November in southern France. Luckily, we still don’t have a lot of mosquito activity during the winter, contrary to northern Italy where a small population is still active in January.”
Read more: Record dengue cases recorded in France - how to prevent the spread
Act now to combat mosquitoes in 2025
There are measures people can put in place now to tackle mosquitoes in 2025, Mr Lacour said. These include:
Sponge cleaning the inside of containers where mosquitoes like to spend time during winter to remove the tiny eggs laid in them. These include water collection barrels, planters, drain pipes, and gutters made of concrete. You can spray the insides with boiling water (but avoid boiling water on plastic).
Put April 16, 2025 in your diary and make it a “tiger mosquito hunting day “in your garden or terrace. “April 16 is a prime date for seeing larvae with the naked eye in containers before the first females emerge,” Mr Lacour said. Get rid of them by emptying water, removing larvae with a landing net or by scalding them. You can also treat them with Bti (Bacillus thuringiensis israelensis), a naturally occurring soil bacterium that can effectively kill mosquito larvae present in water.
Do not wait for the first bites to take action as that risks you “having to wait a few weeks for the death of mosquitoes that have already emerged (a death that can be hastened by using effective traps),” said Mr Lacour.
Frédéric Simard, research director for the Institut de Recherche pour le Développement (the French National Research Institute for Sustainable Development), Montpellier, said the period of activity for mosquitoes, and tiger mosquitoes in particular, has become longer.
“We realise that the reinforced official surveillance period runs from May 1 to November 30. We start seeing larvae as early as April, and we're still being bitten by mosquitoes after November,” he told France Info.
“Temperatures are still very mild and there has been abundant rainfall. Cellar flooding, for example, is an excellent breeding ground for the common culex mosquito.”
The insects eventually stop biting when the number of daily hours of daylight falls below a certain level.
“Culex mosquitoes will spend the winter as adults, in cellars or caves, and stop all activity, in a state of hibernation,” said Mr Simard. “And in early spring, they'll come out to lay eggs and create a new generation."
Tiger mosquito eggs should not be allowed to settle in gardens or on balconies, as they are resistant to the cold. They are insensitive to external conditions and are resistant to frost.
You can report mosquito activity here.
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Tiger mosquitoes expand across France
It is believed the tiger mosquito entered Europe via Albania, before reaching Italy in the early 2000s.
Its presence was confirmed in 2004 in the Alpes-Maritimes department, around Menton, Nice and the Camargue, although a few isolated cases were reported in 1999 in Vienne, Val-d'Oise, Seine-et-Marne and Orne.
It was not until 2006 that authorities began to worry about the consequences of the insect’s presence.
At that time, Réunion Island was hit by a major chikungunya epidemic.
More than 200 infected people died between 2005 and 2006.
In September 2010, the first case of dengue fever was officially detected in Nice (Alpes-Maritimes) and announced by the French Ministry of Health. It was an “isolated case” and the patient recovered.
Shortly afterwards, two ‘autochthonous’ cases (when a person has not travelled in the 15 days preceding clinical signs) of chikungunya were detected in the Var department, confirming the insect's presence in the south of France.
Since then, the presence of tiger mosquitoes has continued to grow: it was found in Occitanie in 2011, Auvergne-Rhône-Alpes and Nouvelle-Aquitaine in 2012, Bourgogne-Franche-Comté in 2014, Grand Est, Pays de la Loire and Île-de-France in 2015, Centre-Val de Loire and Hauts-de-France in 2017, Bretagne in 2021.
By 2024 departments in mainland France were affected by the presence of the tiger mosquito.
Read more: MAP: Where tiger mosquitoes have spread to in France
