Processionary caterpillars in France: how to protect your dog

Dog owners in France are being cautioned that processionary caterpillars may prove fatal to their pets, with a veterinary surgeon issuing a warning as increasingly mild temperatures prompt the insects to emerge earlier than usual.

Processionary caterpillars are small red/brown insects, with tiny hairs all over their bodies that can cause major irritation, damage and respiratory problems to adults, children, and pets. They are usually seen on tree trunks or on the ground in their namesake ‘procession’ lines, and were officially classified as a ‘harmful species’ in 2022.

There are two types, with overlapping seasons:

• Pine caterpillars (processionnaires du pin): January to May, with a peak in March

• Oak caterpillars (processionnaires du chêne): April to August, with a peak in June

Mild temperatures, blamed on climate change, have caused the insects to start emerging earlier this year, especially in the regions of Brittany and Grand Est.

Danger to dogs

Dogs are among the animals most commonly affected, said veterinarian Laetitia Barlerin, to TF1 on February 23, as their attention is particularly drawn by the caterpillars when the insects crawl down from trees onto the ground.

When the dog goes to investigate, inevitably using its mouth, it licks or ingests the hairs of the insects and immediately feels a sharp burning sensation. 

Dogs can also get the hairs in their eyes or swallow the insects, leading to conjunctivitis and, in some cases, severe digestive upset.

Caterpillar symptoms

Signs of problems, and that your dog has come into contact with the caterpillars, include:

• excess drooling (more than usual)

• swollen lips and/or tongue and/or nasal cavity

• black, red, or grey tongue

• inflamed eyes

• violent vomiting

• inflammation or irritation on skin around the ears

• coughing or throat irritation

• allergic shock symptoms such as fever, lethargy, heavy breathing

“Ultimately, [the caterpillar hairs] destroy the tongue; it necrotises,” she said. “The dog can lose its tongue, which is why there is a real danger.” 

Cats are less likely to be affected, because they are more likely to be afraid of the caterpillars and stay away from them.

What if my dog comes into contact with the caterpillars? 

“This is a life-threatening emergency,” said Dr Barlerin. 

Owners should:

• Rinse the dog’s mouth with water using a hose or shower head to remove as many of the caterpillars' stinging hairs as possible.

• Take the dog to their vet, or the closest vet, immediately.

“The dog may be hospitalised for several days while we try to save their tongue,” said Dr Barlerin.

The vet may also administer an antihistamine, an anti-inflammatory (usually cortisone), and/or proceed to other treatments, particularly if there is swelling, signs of an allergic reaction, or signs of dying tissue.

How can I prevent contact with the caterpillars in the first instance?

There is a higher risk of the caterpillars in forested areas, particularly those with pine or oak trees. Avoiding walks in these areas can help prevent your dog from coming into contact with the insects.

Keep your dog on a lead and pull them away sharply if you see any caterpillars.

If you notice the processionary caterpillar nests (which look like balls of cotton wool in the trees) in your garden or land, the official Chenilles-Risque website advises that people destroy their nests, after notifying authorities of their presence. You can use traps purchased at garden centres or through professionals to prevent the caterpillars from reaching the ground.

“You can also use a biological treatment based on bacteria that kills processionary caterpillars,” said Dr Barlerin.

Chemical solutions are also possible and cutting down trees where the animals are present is a last resort (although these may harm other species, and may be prohibited by local regulations).

Never touch the caterpillars with bare hands, even when the insects are dead, as their hairs can still irritate. If you are concerned about removing the insects, professional gardeners can help.

To notify authorities of processionary caterpillars, use the official open-access website (or smartphone app). You can also call or email your local mairie to inform them of the sighting.

In some regions, such as Brittany, prefectural decrees state caterpillar sightings must be reported (although there are no penalties for not doing so). In some cases nests may be destroyed, but only if this is deemed necessary for the local environment or due to local health risks. 

In several communes, this is done through natural measures, including installation of nests for birds (blue tits are among the main predators of processionary caterpillars). Workers may also cut down nests.