Processionary caterpillars already out in January: beware of danger!

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The arrival of processionary caterpillars starts earlier and earlier. When they leave their nests, they cause multiple problems for nature, animals, but also for humans. Here’s how to recognize it, which regions are most affected and what the risks to your health are.

Processionary caterpillars: what are they?

You have certainly already seen these funny little caterpillars. They measure 3 to 4 cm and are black in color with a brown stripe above their body, some can be entirely silver. They have the particularity of being all hairy and moving in single file. It is very rare to see them alone.

They were classified as harmful in April 2022 by Decree No. 2022-686, throughout France. Indeed, in addition to devastating the trees on which they weave their cocoons, the hairs of these caterpillars are also very stinging for domestic animals and humans.

Several kinds of processionary caterpillars exist, but in France, only two species are listed:

Thaumetopoea pytiocampa (the brown and brown pine processionary caterpillar); Thaumetopoea processionea (the gray oak processionary caterpillar).

As their name indicates, the different species have preferences: the moths which will lay their larvae on conifers will give birth to pine processionary caterpillars and those which will lay their larvae on deciduous trees will give birth to processionary caterpillars. of the oak family. However, their mode of operation remains the same: the caterpillars weave larger or smaller nests depending on the number of eggs laid. They sleep there during the day and only come out at night to eat the leaves.

If the processionary caterpillars of the oak spend their life in the tree, those of the pine will descend during the last larval stage. This is when they will be visible, since they will bury themselves in the ground to transform into a chrysalis to become a butterfly.

Which departments are most affected by the proliferation of processionary caterpillars?

There was a time when the pine processionary caterpillar remained camped around the Mediterranean, or even on the Atlantic coast. It is clear that global warming invites this pest to return to the land, favoring reproduction, egg laying and the hatching of larvae. ONERC (National Observatory on the Effects of Global Warming) now uses the proliferation of these individuals as a biomarker.

Oak processionary caterpillars, for their part, were only widespread in northern France. But they ended up descending little by little, still sparing certain regions of the south of France.

To put it simply, no French department is spared from processionary caterpillars: they have invaded the entire metropolis. Some even record the presence of both species!

When do processionary caterpillars come down from the tree?

Pine processionary caterpillars begin to descend from the nest from January to March. This third month of the year is the most favorable for the procession. However, mild winters lead to early hatching and therefore earlier descent. It is not uncommon to see them already on the trunks from the beginning of January in certain regions.

It is therefore advisable to exercise caution, because the lines of processionary caterpillars can stretch over several meters, sometimes numbering more than 300 individuals and are not without health consequences.

The dangers of processionary caterpillars

If you must prune your trees, be careful not to touch the nests, because even if there are no caterpillars, their stinging hairs may still be in the cocoons. Prefer to call a professional who will have the necessary equipment to remove the nests without risk. Also note that it is not necessary to touch a caterpillar to be a victim of its effects! The wind carries pieces of nests which can land on your laundry, your terrace, your gardening equipment, the hair of your animals or even on your crops.

On the other hand, if she feels threatened, her hair will automatically detach from her body. Being very thin, they are very volatile and can travel tens of meters! They contain a protein called thaumetopoein which is toxic, irritant and inflammatory. According to ANSES, it is spread by the hair where it is planted, that is to say on the skin in 90% of cases. However, it happens that they get stuck in the eye, in the mouth or even in the nose.

When thaumetopoein is released, it causes a patch of burning, itchy red bumps, similar to a nettle sting. Some people also suffer from a drop in blood pressure, discomfort and even loss of consciousness. It is especially the hairs in the eyes which are very dangerous, since in addition to pain and tears, the eyelids can swell, damage to the cornea has already been recorded, as well as lasting vision problems.

When inhaled, the hairs of processionary caterpillars can also lead to coughing fits, runny noses, sneezing, and even asthma attacks. Finally, ingestion of hairs, more often in young children, can cause localized edema, as well as breathing difficulties. In dogs, inflammatory reactions can be very serious and can lead to necrosis of the tongue if they eat a caterpillar.

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