Insect plague: toxic caterpillars in summer

Toxic caterpillars are often found in The Hague in the period from May through June. They can pose a health risk in people and animals if they come into contact with the hairs.

Recognising the caterpillar

Once the larvae have hatched, they are first orange and then later grey-green with a light stripe on both sides. The adult caterpillars are blue-grey on their back and green-grey on their underside. The head is black-brown. Their body is covered with long white hairs contrasting with shorter hairs. The shorter hairs which easily break off are the bristles. As the name suggests this caterpillar is found almost exclusively on oak trees. Large groups of them can eat all the foliage in the tree in just a short time. This is usually no problem for the tree; it recovers once the caterpillars pupate into adult moths. But they can be highly irritating to people and animals.

Health complaints

The Oak Processionary moth caterpillars have approximately 700,000 bristles. These hairs break off as barbs and can be carried by the wind and get into skin or clothing. People usually get a painful red rash and skin irritation within 8 hours if they come in contact with the caterpillar. This can last 2 weeks. It can cause painful, red and itchy swollen eyes within a few hours. It can also lead to breathing difficulties. Animals, especially dogs and horses, can also experience similar health problems.

What can you do about the complaints?

The health complaints usually go away within 2 weeks. Do not scratch or rub the affected area. Wash or rinse the skin or eyes with water and wash your clothes on a high temperature (60 degrees or more). If your skin is very irritated you can use a soothing cream containing menthol or aloe vera. In the event of serious health complaints, go to your general practitioner. For more information about the health effects, contact the Public Health Department (GGD Haaglanden).

Report caterpillars

If you think you have seen a nest with Oak Processionary moth caterpillars, report this to the municipality online or contact the municipality. If you use the online Melding openbare ruimte form, select ‘Nee’ for the question 'Komt uw melding overeen met 1 van de volgende onderwerpen?'. Then select 'Dieren en hondenpoep' and 'Eikenprocessierups'.

The municipality will have the nests removed as quickly as possible by a professional company.

Caterpillars crawling over the bark of a tree.
Caterpillars crawling over the bark of a tree.

Published: 3 July 2019Modified: 27 March 2020