Processionary caterpillars are invading several French regions this week, prompting municipal authorities to issue urgent public health warnings [1, 2].

The infestation is significant because the caterpillars' hairs are highly urticant, meaning they cause severe itchy skin reactions in humans and animals [1, 5]. Health agencies said residents should remain vigilant and avoid contact with the larvae as they move in large groups.

Reports indicate the invasion is particularly strong in the southern Yvelines and the Vallée de l’Eure within the Île-de-France region [2, 3]. Local officials in these areas said the current outbreak is massive and stronger than usual [2, 3]. Other affected areas include the Île de Bréhat in Côtes-d’Armor [4], with some reports suggesting the phenomenon is spreading across the whole of France [6].

Municipalities are coordinating control actions to manage the pest population and protect public spaces [2, 3]. These efforts aim to reduce the risk to children and adults who frequent forests and parks during the late May period [1, 2].

While some reports focus on the concentration of the pests in southern Yvelines, others indicate a broader national trend [2, 6]. The resurgence is linked to seasonal patterns of the Thaumetopoea species [1, 5].

Authorities said the public should avoid touching the caterpillars or their nests. Because the hairs can become airborne, the risk of irritation extends beyond direct physical contact [1, 5].

“The hairs are highly urticant”

The unusual intensity of this outbreak suggests a potential shift in seasonal pest dynamics or environmental conditions in France. By classifying the invasion as stronger than usual, municipal authorities are signaling that standard preventive measures may be insufficient, necessitating more aggressive intervention to prevent widespread public health irritations.