Pine processionary caterpillars soon expected in some areas of France: protect your garden and pets

People in the western half of France may soon see the early return of poisonous ‘pine’ processionary caterpillars. 

There are two main types of processionary caterpillars: those that build their nests in oak trees (processionnaire du chêne), and those that nest in pine trees (processionnaire du pin).

The latter, identifiable by their red markings, are set to enter a new stage of their life cycle in some ‘oceanic’ areas of France, with the caterpillars leaving their treetop nests in long lines, or ‘processions’, and moving across the ground to burrow into the soil.

The timing varies across France depending on the climate.

If caterpillars mature before winter, during a particularly mild autumn, a first wave of early processions can happen from mid-October until mid-December. 

This is rare and the majority of the caterpillars are more commonly seen between February and early May.

Adult moths usually lay their eggs between June and September. Eggs typically hatch between late July and early November depending on local conditions, and the caterpillars mainly build their nests from October to February. 

When and where are they found? 

They are now found across much of mainland France.

FREDON France, France’s NGO for plant health, environment protection and surveillance, developed a map in 2023 illustrating when you may see pine processionary caterpillars in different parts of the country.

The earlier processions occur particularly in areas with ‘oceanic’ (coloured gold on the map) and ‘altered oceanic’ (coloured blue) climates - although exact timings can change.

Météo-France describes the oceanic climate as being characterised by “mild temperatures and relatively high rainfall linked to weather systems coming in from the Atlantic,” found in Brittany and along France’s northern and western coasts.

The altered oceanic climate happens in central transitional zones between coastal and mountain areas including most of Ile-de-France, the Hauts-de-France and some of the Massif Central. There is less rainfall and greater differences in temperature between winter and summer. 

In continental and mountain areas, processions mainly occur from mid-February to mid-May.

In Mediterranean areas, the main period is February and March. 

Why are they dangerous?

Pine processionary caterpillars develop tiny urticating hairs as they grow. These hairs can cause painful reactions if they come into contact with the skin, eyes or mouth.

You do not even have to touch them to be affected. The hairs can become airborne or be left on vegetation, the ground and other surfaces around infested trees.

Reactions can include skin irritation, swelling and eye problems. More serious exposure can cause breathing difficulties or other severe reactions.

The hairs can also remain active in old nests for several years, meaning that people should not approach or handle abandoned nests even if no caterpillars are visible.

How can you protect your garden?

When in your garden, you should avoid touching the caterpillars or their nests and keep children and pets away from affected trees and areas. 

FREDON France recommends using professionals to remove nests or manage infestations, particularly where people or animals are present.

Several methods can be used, including traps placed around tree trunks to catch caterpillars as they come down, as well as pheromone traps targeting adult male moths.

If you have pine trees in your garden, check them regularly for nests, but do not approach or handle them.

What about dogs and cats?

Caterpillars can be very dangerous for pets and potentially fatal as they may try to sniff, lick or eat the caterpillars.

Signs of exposure can include heavy drooling, vomiting and swelling of the tongue or lips. More serious cases can cause eye injuries, breathing difficulties or tissue damage.

If you think your pet has come into contact with processionary caterpillars, you should rinse its mouth with cold water for 10 to 15 minutes wearing gloves and contact a vet as quickly as possible.