Little nuisance expected from poisonous caterpillars next year

The nuisance caused by the oak processionary caterpillar was not too bad this year, and researchers also expect "low pest pressure" next year. However, there may be local "hotspots" that cause a lot of nuisance, the Oak Processionary Caterpillar Knowledge Center reported on Wednesday.

Far fewer oak processionary butterflies were found per trap last year. The number fell to the lowest level in 14 years. "Based on the number of butterflies, we can conclude that few egg packets have been deposited," biologist Arnold van Vliet of Wageningen University (WUR) explained. This means that there will probably be fewer caterpillars in the trees next year, and therefore, people will be less bothered by the stinging hairs.

However, they are uncertain about one factor. The researchers do not know how many caterpillars are underground. "They can have a longer rest phase underground," said Van Vliet. "Pest pressure can increase quickly if the caterpillars emerge in June.”

The highest peak of nuisance from the oak processionary caterpillar was seen in 2019 when many people went to the doctor because they were suffering from itching or problems with their eyes or respiratory tract. Significantly fewer people are now affected.

The knowledge center noted that the weather played a role this year. People spent less time outside because there was a lot of rain in June, which meant there was less chance of them coming into contact with the stinging hairs.

The decline in the oak processionary caterpillar and butterfly is partly due to management measures taken by municipalities and provinces. The Oak Processionary Caterpillar Knowledge Center also sees that there were successful measures to promote the natural enemy. Parasites, bats and birds, among others, can combat the oak processionary caterpillar.