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Processionary caterpillars now officially a harmful species in France

A decree recognises oak and pine caterpillars as causing severe irritation and respiratory issues in humans and pets – here are tips for avoiding them

The little caterpillars can often be seen in their namesake “lines” on the ground or up tree trunks Pic: Gonzalo Jara / Shutterstock

Processionary caterpillars, whose tiny hairs can cause irritation and respiratory problems, have been officially recognised as a harmful species in France in a new decree.

The decree from April 27 confirms that the caterpillars, chenilles processionnaires in French, have been added to the “list of species of which the spread damages human health”.

The decree includes two types of caterpillar: the oak processionary caterpillar (la chenille processionnaire du chêne) and the pine processionary caterpillar (la chenille processionnaire du pin).

The little caterpillars can usually be recognised because of their tendency to travel in “lines” (or processions) on the ground and up tree trunks. They have tiny hairs all over their body, which can be damaging to humans and pets if touched or ingested. 

Their nests, which are made in trees, look similar to cotton wool.

The new decree has been issued due to a major increase in “yearly reports of caterpillar intoxication” at anti-poison centres between 2012 and 2019, said the public office website Vie-publique.fr. The number of reports has risen from 44 to 178 per year, it said.

Marilou Mottet, coordinator at the national observatory for the caterpillars, explained to Le Parisien that the official recognition of the caterpillars’ damaging effects means that “prefects will, in each department concerned, be able to warn the population, and explain the measures to take if they see nests above play areas or school playgrounds”.

Pine caterpillars tend to affect people the most from December to April, while the oak affects people more from May to July, said the l'Agence régionale de santé (ARS) of Île-de-France. 

Their tiny hairs can easily come off when touched, or can simply blow into the air, and be spread by wind.

Symptoms of irritation include: 

  • Painful, severely itchy rash within eight hours of skin contact;
  • Conjunctivitis (red, painful, watery eyes) within one to four hours in case of eye contact;
  • Sneezing, sore throat, difficulty swallowing and possibly breathing difficulties if inhaled;
  • Hypersalivation, vomiting and abdominal pain if ingested. 

The ARS advises people “not to approach or touch these caterpillars or their nests”.

It also advises: 

  • Wear long clothes when walking in the forest
  • Avoid rubbing your eyes during or after a walk
  • Wash fruit and vegetables from your garden
  • Avoid drying clothes next to infested trees
  • Take a shower and change your clothes if you suspect you have been exposed to the caterpillars.

The caterpillars can also be dangerous (even fatal) to pets such as dogs and cats if they are touched or eaten.

Read more: What to do if your pet is hurt by processionary caterpillars in France  

The caterpillars can be deterred or killed with fire or insecticide, and they are eaten by birds. Traps that attract the processionary lines are also available.

Due to the risk, some authorities in badly-affected areas are starting to take action, especially as experts are predicting a rise in the caterpillar population in 2022 and 2023.

Forest health department le Département de la santé des forêts in Aveyron, Occitanie said: “At this stage, specialists are predicting a peak next year.”

Read more: Local authorities act as toxic caterpillars appear again in France 

The department uses a type of natural, bacterial insecticide to fight against the caterpillars, called BTK (Bacillus thuringiensis), which is toxic to insects and caterpillars but not humans. It must be used in autumn for maximum effect. 

Authorities have also installed predator boxes and eco-friendly traps especially designed for the chenilles.

One town even went further. 

In 2018, the mairie of Millau (Aveyron, Occitanie) took out a decree stating that people who did not take steps to help eradicate the caterpillars would risk a fine. Residents who did not take part in the local anti-chenille measures were first sent a letter recommending ways to destroy the nests or trap the caterpillars. Further inaction would then lead to a €38 fine.

Residents also joined together to make group purchases of traps in particularly badly affected areas.

The caterpillars used to be seen only in the south of the country near the Mediterranean basin, but are now spreading across France, including in Normandy, Brittany, and Grand Est.

Related articles

Two types of processionary caterpillars gaining ground in France 

Toxic processionary caterpillars in France already 

Processionary caterpillars spotted in France already 

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