- In Bas-Rhin, Hauts-de-France, Ile-de-France and in many other regions still, the nest destruction companies of Asian wasps and hornets say they have to deal with levels of activity records.
- The reason is not so much the confinement or a very mild winter, explains entomologist Quentin Rome, but much more the fact that winter and last spring went smoothly on the temperature front.
- For Quentin Rome, there is in any case nothing intriguing: "there are years without wasps and others with, we have known for a long time", he indicates. And this proliferation this summer does not say anything about an improvement in the state of biodiversity.
They disrupt somebody's barbecues, spoil others' selfies and sometimes sting too. "They" are the wasps, which many French people complain about, on social networks this summer.
Are they more numerous this year? The resurgence of activity experienced by companies specializing in the destruction of wasp and hornet nests tends to show this. In the Bas-Rhin, one of them, DMKExpert, interviewed by AFP, estimates the increase in activity at 300%. In Angers, in the Val d'Oise, or on the coast of Nord-Pas-de-Calais, other companies are also talking about a record summer in the columns of the local press. Often with two factors put forward to explain this proliferation: a very mild winter and confinement.
Really ? Quentin Rome, entomologist of the UMS PatriNat at the National Museum of Natural History (MNHN), specialist in hymenoptera (wasps, hornets, bees, bumblebees), answers the questions of 20 Minutes .
Can we already say, without being mistaken, that there are more wasps this summer than usual?
To be honest, this feeling of being invaded by wasps returns every summer, even in years marked by declines in the insect population. Last summer, around the same time, I had received requests for an interview on the same subject when we were in a year marked by significant drops in wasp populations. How to explain it? Quite simply because, commonly, in France, wasps are summarized in two species: Germanic and common. These two species are very interested in our food and very present in urban and peri-urban areas. Hence the impression that they invade us as soon as we start to eat outside.
But is it still just an impression?
No. Indeed, some years, the wasps are more numerous. Unfortunately, there are no statistical studies that allow precise monitoring of populations, simply because this insect does not interest many people. On the other hand, we know that the common and Germanic wasps have the same life cycle, the same biology, the same preferences as the Asian hornet. However, the latter is the subject of much more extensive monitoring in France because it is an invasive species.
By extrapolating, this monitoring of the Asian hornet allows us to have an idea of the evolution of wasps populations in France, which we then refine with observations brought back from the field. It is thus estimated that in 2019, the wasp populations had dropped by three compared to 2018. It is still too early to make the estimates for 2020, since we are still in the middle of the seasons for wasps, but we could be close , this time, a fivefold increase in populations compared to 2019.
How to explain it? Is this actually the result of confinement and a very mild winter?
I do not quite understand what makes it say that containment has had a positive impact on wasp populations. I would tend to say the opposite. The confinement meant that we spent a lot more time in our gardens, near the parks ... So much so that wasp nests were detected earlier than usual. I noticed it in any case for the Asian hornet, of which I am in charge of the follow-up in France: I received peaks of reports of nests the first weeks of confinement, whether they are young nests or nests from previous years. that had not been discovered.
And the mild winter?
It is not that much, either, which explains the strong presence of bees this summer. Of course, a very harsh winter will lead to excess mortality among wasps, but they can withstand very low temperatures all the same. They survive frost without too much concern, for example.
On the other hand, what matters to them much more is to have a winter and a spring with stable temperatures. And that's what we got this year. Keep in mind that wasps have a very specific annual life cycle. A colony starts with a single queen who will wake up in the spring, found her nest and raise her brood. Gradually, the colony grows to explode around July-August. The populations then stabilize before gradually decreasing in October and November.
Unusual temperature variations can disrupt this cycle. Warming during winter - as we have experienced in the South in recent years, with 20 ° C at the end of December followed by periods of frost - will wake up some dormant queens who will find nothing to eat and will then have a high chance of dying. . Likewise, the late frosts that we experienced in spring 2019 in several regions of France have most certainly also led to excess mortality among queens.
What reflex to have, then, when faced with wasps? Can we live with them?
They play a far from negligible role in maintaining biodiversity. We often insist on that of bees, because pollinators [they carry pollen grains allowing to fertilize plants]. But many other insects do it too. This is the case with wasps. And they're not limited to that. They are also predators of insects, and they tend to focus on the ones that swarm the most. Typically caterpillars on a tree. As such, wasps are great regulators.
So I am not for the systematic destruction of the wasps that bother us. Of course, when a nest presents a danger - when it is in a passageway, for example - the reflex is the same as for a swarm of bees: you have to call in a professional to remove it. If you're just dealing with insistent wasps hovering around the table, one solution is to sacrifice part of your meal to them. A quarter of an hour before starting to eat, a piece of fruit or meat is placed three or four meters from the table on which the wasps will get used to coming. We then eat more quietly.
Is this good year for wasps good news for biodiversity?
No, we can't say that. The increase observed this year is a cyclical phenomenon, linked to the weather. There are years with and years without, there is nothing intriguing, we have known that for a long time. Above all, it is not because the common wasp and the German wasp are well that it is thus for all the hymenoptera. Like other insects, globally they continue to crack their mouths, mainly because of intensive agriculture. The trend is expected to continue this year. The proliferation of the Asian hornet, for example, is bad news for bees, of which they are prey. It has been as long as it has not rained in normal amounts in France, so it is to be expected that the trees will give less fruit and the flowers less nectar. There may be a resource problem for many insects. Here again, the stake is not so much for the common wasp, the German wasp or the Asian hornet, which come a lot to seek their food in our sugary foods. Other Hymenoptera also have this ability, but do much less and tend to prefer flowers.
Planet
United States: Washington State under threat from giant hornets
Planet
Ariège: He had lost two million bees due to spraying, intoxication recognized by justice
- Animals
- Biodiversity
- summer
- Insect
- Planet