Oak processionary caterpillar outbreak in Brittany raises health warnings

The Regional Health Agency of Brittany (ARS) has warned of an exceptional surge of oak processionary caterpillars in the department of Plouvien and surrounding areas. The density of nests this spring‑summer 2026 rivals the 2007 outbreak, prompting state services, local authorities and partners to implement control measures and issue public guidance.

The caterpillars’ urticating hairs can cause skin rashes, conjunctivitis, respiratory irritation and, in rare cases, more severe reactions. Residents are advised not to touch nests, avoid picnicking under infested trees, keep children and pets away, wear protective clothing and seek medical attention for significant symptoms.

A companion guide on yellow and green garden caterpillars notes that many species are harmless, but stresses the importance of distinguishing them from the processionary varieties, which are classified as a health‑risk species by regional health agencies.