Achtung! Poisonous caterpillars are surging across Swiss forests

While the creepy-crawly is not new to the alpine nation, reports warn that the poisonous oak processionary moth (OPM) caterpillar is particularly prevalent in Switzerland this summer.

Oak processionary caterpillars surging in eastern Switzerland

The Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) has urged residents to stay cautious as there is an “exceptionally severe OPM infestation [this] year.”

The caterpillar has been found in several cantons, particularly in Schaffhausen and eastern Switzerland, where “for the first time, an entire section of forest [...] has been infested,” reports SRF. The cause of its rising presence is thought to be the dry, warm weather in spring, which created the perfect conditions for infestations. 

You can spot an oak processionary moth nest by looking out for large white-grey webs on oak trees, particularly branches and tree trunks, or for large areas of trees that look like they’ve been eaten.

Caterpillar rash symptoms and treatment

While it’s not necessarily the caterpillars themselves that cause harm, the several thousands of hairs can make their way into the air and come into contact with humans and animals. In 2024, 13 children were hospitalised with allergic reactions. 

The hairs contain a toxin that can cause an allergic reaction or a bad skin rash known as caterpillar dermatitis. Symptoms may include “redness, itching, and blisters, as well as irritation of the mucous membranes of the mouth, nose, and eyes. Other possible symptoms are fever, dizziness, and fatigue. And in rare cases, anaphylactic shock,” continues SRF. 

If you think you’ve come into contact with the caterpillar’s hairs: do not touch your eyes or hair, try to remove hairs with adhesive tape, rinse the area, change and wash your clothes and take a shower.

Consult your doctor about how to treat potential symptoms or reach out to Tox Info Suisse on 145. In a medical emergency, call 144.

Take precautions against the poisonous caterpillar

If you’re planning a hike or a weekend picnic in a forest, then it’s best to be aware and look out for potential nests. If you come across one, stay as far away as possible and avoid all contact. Keep dogs on a lead as they can also be affected.

Covering your skin can also help reduce the chance of coming into contact with the caterpillar hairs. Local authorities may close the area if a nest or infestation has been reported. Look out for signs for “Eichenprozessionsspinner” or “Chenille processionnaire du chêne”.