The processionary caterpillar comes from the Lepidoptera family. This is a larva of “Thaumetopée”, a moth whose female can lay up to 300 eggs in pines or oaks. Black and yellow with long white hairs, she measures only a few centimeters.
The hatching of the caterpillars usually takes place between 30 and 45 days after laying, in the spring. They group together and make a very light silk shelter at the branch level. It is at nightfall that the insect will feed by nibbling the leaves of the tree, forming a procession, leaving behind a network of threads and Chenilles processionnaires yvelines.
In summer, the caterpillars weave a more resistant nest composed of silky threads veneered on the trunks and main branches which can reach a significant size (one meter in length and more). Then the caterpillars leave their shelter to reach the ground. The colony moves in a long line, sticking to each other. Once they are in a sunny location, they hide in the ground. After two weeks underground, the insects weave individual cocoons, then change into pupae. This form can last for months or even years.

What are the dangers ?

Small, but very harmful to animals and people, caterpillars kill several people every year. Their hairs are very stinging. The caterpillars remain harmless as long as there is no direct contact.
The most formidable variety is the caterpillar of the oak “Thaumetopoea processionea” whose mode of defense is particularly effective. It preserves its orange and microscopic hairs in pockets called “mirrors”. There are some on each dorsal segment. If ever the insect detects a phase of danger or undergoes stress, it opens its “mirrors” and releases thousands of stinging hairs of a few microns, like fine dust.

With activation of the insect’s defense traderinput mechanism, the hairs can remain suspended in the air or be carried by the wind and easily penetrate the skin, respiratory tracts and even the eyes.
Skin contact with these stinging hairs can cause:


    • Painful rashes: burning, itching, irritation, inflammation.
    • Violent allergic reactions: asthma, edema, even anaphylactic shock.
    • In the event of contact with the eyes: conjunctivitis (painful, red and watery eyes), or even temporary blindness appears when a hair sinks into the tissues of the eye after rubbing.

The reaction appears shortly after the incident.

In case of symptoms, it is necessary to contact 15 or go to the emergency room. As the risks are more severe for pets, it is important to contact veterinary emergencies.

How to protect yourself from it?


      • Avoid contact with processionary caterpillars and their nests,
      • Avoid frequenting places near infested pines or oaks,
      • Put on covering clothes, if it is compulsory to go to a potentially infested area,
      • Do not sweep them to avoid forming a cloud of stinging hairs which may cause respiratory, eye or skin damage.


Note that insectivorous birds such as cuckoos, hoopoes or chickadees are the natural adversaries of processionary caterpillars. It is often necessary to destroy these caterpillars. For this, there are mainly chemical means making use of insecticides or biological care such as products based on bacillus thuringiensis as well as mechanical formulas such as burning or cutting branches of trees or nests.

Inform yourself:


      • National Agency for Food, Environmental and Occupational Health Safety (ANSES)

Several regional health agencies (ARS) have also published alerts on their website:

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