Oak processionary caterpillar

What is it?

The oak processionary caterpillar is the larva of a moth. This moth lays its eggs in the tops of oak trees in particular. The caterpillars hatch from the eggs between April and early May. Initially, the caterpillars are high up in the tree. After several moults, groups of caterpillars come together. They form large nests on the trunks of oak trees. These nests consist of a dense web of threads, stinging hairs, moulted skins and excrement. At night, the caterpillars leave their nests in procession (in a line) in search of food.

Health complaints

The venom of the oak processionary caterpillar is contained in its stinging hairs. A fully grown caterpillar has around 700,000 of these hairs! These hairs are invisible to the naked eye. With their barbs, the arrow-shaped stinging hairs easily penetrate the skin, eyes, and respiratory tract when touched.

Contact with stinging hairs can cause symptoms within a few hours, such as (severe) itching, bumps, blisters, redness, and inflammation. The eyes may become red and swollen and/or inflamed. Symptoms similar to those of a cold may occur: a runny nose, tickle in the throat, coughing, difficulty swallowing, and shortness of breath. In addition, general symptoms such as vomiting, dizziness, fever, and general malaise may occur. The nuisance caused by the caterpillar's stinging hairs usually starts in May and continues through August.

What can you do yourself?

If you have symptoms, it is important to prevent the stinging hairs from spreading further across the body:

Remove the skin with adhesive tape. Do this immediately after exposure. Then rinse the skin and eyes with lukewarm water.
The stinging hairs are not easy to remove from clothing. It is best to wash clothing contaminated with stinging hairs very thoroughly (preferably at 60ºC).

The symptoms usually disappear on their own within a few days to two weeks. In case of severe itching, anti-itch remedies such as menthol-based ointments can provide relief. If the symptoms are more severe, it is advisable to consult your doctor.

How can you prevent problems?

When visiting a nature reserve where oak processionary caterpillars are present, ensure that your neck, arms, and legs are well covered. Do not sit on the ground.
Try to avoid direct contact with caterpillars, (old) stinging hairs, spider webs, and molted skins as much as possible (this also applies to pets).
Make children aware of the danger posed by oak processionary caterpillars.
Avoid roads lined with oak trees that have lots of processionary caterpillars. Old nests from last year also contain lots of stinging hairs, which can be blown away by the wind.