How the heatwave has affected mosquitoes in France
Their numbers change depending on heat, rain, and stagnant water
Mosquitoes thrive under warm temperatures but not at extreme heat
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The recent heatwave in France has affected mosquito activity, as people notice fewer mosquitoes than usual, even with doors and windows left open.
Mosquitoes are cold-blooded so their life-cycle depends on temperature.
When it is warm, they develop faster. Eggs hatch more quickly, and the larvae (the mosquito’s early life stage that lives in water) grow faster.
After the larval stage, they become pupae, and then adult mosquitoes emerge. In species such as Aedes albopictus (tiger mosquito), a few days of warm weather can shorten this whole cycle.
However, very high temperatures can also have the opposite effect. Around 35C and above, mosquitoes become stressed. They can lose water more quickly, become less active, and in some cases die sooner.
During the hottest hours of the day, mosquitoes tend to hide in cooler, shaded places. But it’s not just the heat that reduces their numbers.
The recent heatwave in France also brought a long period of dry weather. Mosquitoes need stagnant water to lay their eggs. During hot and dry periods, many breeding sites disappear, which can reduce mosquito populations.
Conditions can quickly change with the first rainfall. Small amounts of standing water in gardens, gutters, or containers are enough for mosquitoes to breed again.
This is especially true for tiger mosquitoes, whose eggs can be extremely resilient to warm weather, awaiting the first rainfall to hatch.
This means vigilance is needed when rainfalls return, as tiger mosquitoes also carry diseases such as dengue, chikungunya, and Zika virus.
