Pine processionary caterpillars: should we raze the forests of South Aveyron

Pine processionary caterpillars: should we raze the forests of South Aveyron
Pine processionary caterpillars: should we raze the forests of South Aveyron

Particularly stinging and potentially fatal for dogs or cats, processionary caterpillars return to the forests of the Causses. How to fight? The answer with the Grands Causses PNR.

A new incarnation of overheating nature, the processionary caterpillar has reappeared in South Aveyron, taking advantage of the first sunny days and a mercury hovering around 20°C to get back into action.

Particularly stinging, potentially fatal for dogs or cats, this moth larva haunts the canopies of the Causses forests in winter before launching its great transhumance in search of soft soil to complete its transformation.

Well known to hikers, cyclists and trail runners in South Aveyron, the pine processionary has taken up its habits on the Causse Noir or the Causse du Larzac with a peak “very impressive” in 2019. Colonizing more and more spaces.

The impact of global warming

“Contrary to appearances, it is a very old species here,” confirms Laure Jacob, wildlife and flora mission manager for the Grands Causses PNR. Linked to the establishment of black pine around the 1800s. The processionary has since been part of of a life cycle and contributes to a certain balance that must be preserved.”

A balance that the specialist monitors closely. Global winter warming has the effect of seeing colonies multiply that only a temperature of -16°C can eradicate. Values ​​which are now only very rarely achieved in the regions of Western Europe: the area of ​​expansion of Thaumetopoea pityocampa.

Is there any danger in the house? “No,” replies the specialist. “Everyone actually has their own vision of the phenomenon which is linked to their own activity. As lovers of outdoor activities often frequent the same places as the Lepidoptera, sheltered paths on slopes well exposed to the sun, we can have the impression that there are more than last year But if we go a little further into the forest, we will see that there are no or few cocoons.

“We do not eradicate a species”

With a relatively mild winter, it is difficult to anticipate what 2024 has in store for us. Many fear that the Causses will be saturated with caterpillars like in 2019, a year marked by an “extraordinary” quantity of caterpillars. Fortunately, never equaled since? “It’s very difficult to anticipate because it depends on a multiplicity of factors,” recognizes Laure Jacob. But for the moment we have no feedback from the field which could suggest a stronger presence than in past years.”

No more certainties in terms of prophylaxis. “Each stage has its solutions… but no means of prevention, no grandmother’s recipe,” confirms the project manager. There are, however, natural “eco-traps” to install on the trunks of infected trees. They work quite well “.

With the Thuringian bacillus, a biological insecticide to be used only in the presence of the intruder, the PNR recommends the installation of tit boxes, another natural predator of the caterpillar. Funded by the Department, 200 have just been distributed among the most exposed municipalities.

If nothing seems to stop the proliferation of Thaumetopoea pityocampa, whose colonization front is progressing by 5 km per year, why not raze the pine forests of the causses? “Let’s not forget that we are talking about a butterfly larva. Which can move… Furthermore, we do not eradicate a species, argues Laure Jacob. It is part of the life of the forest from which predators benefit , insectivores, the hoopoe, the titmouse… And a whole microfauna which consumes caterpillars.”

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