Their very volatile hairs cause itching, allergies, irritation of the respiratory tract, conjunctivitis, or even inflammation of the mucous membranes which can lead to the death of animals. Processionary caterpillars, whose presence has spread in France in recent years, have just been classified as harmful to human health, via a decree dated April 25 published in the Official Journal on April 27. These species are now present in at least 84 of the 96 French departments.
The two species of processionary caterpillars classified as pests
The two species of processionary caterpillars are classified as harmful, specifies the decree. The pine processionary caterpillar, present on forest floors from December to April, gives way this spring to oak processionary caterpillar, present from April to August on tree trunks. These spring and summer caterpillars are a little less accessible, since they are not present on the ground, but equally stinging and dangerous for animals and humans.
– Observatory of processionary caterpillars
A classification that will force the prefects to act in risk areas
This classification is “A very good news”, rejoices Alice Samama, animator at the Processionary Caterpillar Observatory, created last year. It will indeed allow, and even oblige the prefects to “put in place treatments and strategies to fight against their proliferation”in places where the caterpillars risk affecting people and domestic animals, she explains. “In concrete terms, we are going to have more or less compulsory management depending on the risk”, says Alice Samama. “For example, if caterpillars are observed in a children’s park or a school playground, the prefect will be obliged to act. Conversely, in an uncrowded forestrisk management will not be mandatory.
From the eco-trap to the bacteria via the titmouse, several possible treatments
How can the prefect act? “Different treatments are possible”, explains Alice Samama. To treat the pine processionary caterpillar, which moves on the ground, eco-traps in the form of necklaces can be placed at the bottom of tree trunks: the caterpillars will get stuck in them and will not be able to move on the ground. To treat the oak processionary caterpillar, present until August, rather, the nests should be destroyed. To reduce the presence of both species, “We can also promote the presence of their predators, which are tits and bats”, explains the specialist.
There is also a biological control treatment, with a specific bacterium, called Bacillus thuringiensis. A treatment already used by some municipalities. “This bacterium targets moths of both species, but you have to be very careful because it also targets other species of butterflies”, explains Alice Samama.
The goal is not to eradicate processionary caterpillars – Alice Samama, animator at the observatory of processionary caterpillars
But the specialist warns: “The goal is not to eradicate processionary caterpillars. The species does indeed have predators, which need to eat these caterpillars”, she explains. “If we eradicate them, we remove a link in the food chain, and that could unbalance biodiversity.” Instead, Alice Samama recommends implementing targeted actions, depending on the risk of each territory.