Oak processionary caterpillars on the rise again after years of decline
After years of appearing in fewer and fewer trees, the oak processionary caterpillar is making a comeback in the Netherlands. The caterpillars each have hundreds of thousands of stinging hairs that can cause rashes, skin complaints, and allergic reactions in people and animals.
Experts from the Oak Processionary Caterpillar Knowledge Center checked 60,000 oak trees this year and found the caterpillars in 6 percent of the trees, up from 4.5 percent last year.
The situation is not nearly as bad as in the record year of 2019, when over half of the oak trees in the Netherlands were covered in these caterpillars. But measures are needed to prevent it from coming to that again. The researchers stressed that this is an interim figure, and the percentage will increase if no measures are taken.
“Despite the fact that many people think we have gotten rid of the oak processionary caterpillar, this is not the case,” the knowledge center said. “We will have to get used to always being alert to the presence of the oak processionary caterpillar or of old nests left behind in or under the tree. These nests can still be full of stinging hair.”
According to the knowledge center, there are several possible reasons for the increase in oak processionary caterpillars this year. Many caterpillars that have been lying dormant in ground nests for one or more years seem to have become active again. They often sit low on the trunk of trees that have not yet lost their foliage to the critters. The warm, dry spring also resulted in eggs hatching earlier than usual. And last year’s rainy weather prevented the oak processionary moths from flying far, keeping the eggs concentrated in smaller areas.
That is likely why more caterpillars are being found in some municipalities than others. The experts have come across several hotspots across the country, where they found the caterpillars in almost every oak tree. These include Almere, Steenwijkerland, and the north side of Ede. Large concentrations were also found in Nieuwegein, where the municipality recently urged locals to be alert and report nests.
