What is the oak processionary caterpillar?
The oak processionary caterpillar is the caterpillar of the moth Thaumetopoea processionea. It is common on oak trees in temperate Europe. The hairs of the caterpillar can cause severe skin reactions and eye complaints. The peak of complaints falls in June and July.
Stinging hairs
The problems are caused by the small stinging hairs on the caterpillar’s body. These are about 0.2 mm in size and so invisible to the naked eye. Each caterpillar has many thousands of stinging hairs that can be shot out like an arrow when the caterpillar is threatened, but can also come loose spontaneously. The hairs have tiny barbs and contain the toxin thaumetopoein. Not only the caterpillars themselves are a problem: their nests are also a source of hairs, because the caterpillars moult several times during development and the shed skins with stinging hairs remain in the nests.
What are the skin complaints?
Skin contact with the stinging hairs first gives a small painful wound from the barb attached to the hair. When the hair breaks off, the toxin is released, causing a strongly itchy and burning skin reaction that can sometimes resemble hives. The itch usually does not arise immediately but develops within a few hours. With more extensive exposure, complaints of vomiting and general malaise have also been described. When the hairs reach the eyes, a burning inflammation of the eye membranes develops. Hairs are less likely to reach the airways (nose, throat), but if they do, inflammation and swelling develop there too. Serious allergic reactions with shock signs can occur, but are fortunately rare.
How can the pain and itch be treated?
The skin changes will eventually disappear on their own. The inflammation and itch can be treated with a corticosteroid cream, and cooling lotions (such as calamine) can relieve the complaints. For more serious complaints such as breathlessness and vomiting, it is important to consult a doctor quickly.
Preventing complaints
Wind can carry the stinging hairs to the immediate surroundings of affected oaks, so unsuspecting walkers or cyclists can be exposed, especially in June and July. When infestations are discovered, local authorities usually warn with signs that the caterpillars are active and have the caterpillars and nests professionally removed.
When to see a doctor
See a doctor promptly for breathlessness, vomiting, eye inflammation or a severe reaction after contact with oak processionary caterpillar hairs; a corticosteroid cream helps mild skin reactions.