Oak processionary caterpillar infestation worse than recent years as moth numbers climb

The Netherlands is facing a significantly worse outbreak of the oak processionary caterpillar this year than in recent years, with biologists warning of increased infestations driven by a sharp rise in moth numbers last year and the emergence of caterpillars from underground, RTL reports. Officials say both factors are contributing to heavier infestations and more widespread nuisance across affected regions.

The update comes after monitoring by the Oak Processionary Caterpillar Knowledge Center found the pest in 6 percent of checked oak trees this year, up from 4.5 percent last year.

Each caterpillar carries hundreds of thousands of microscopic stinging hairs, which can cause skin complaints, rashes, and allergic reactions in both people and animals. The hairs can remain active in old nests even after the caterpillars have left the tree.

Researchers examined about 60,000 oak trees nationwide. Although the rise signals renewed spread, experts say the situation remains far below the 2019 peak, when more than half of all oak trees in the Netherlands were affected.

The Knowledge Center cautioned that the current figure is temporary and likely to increase if control measures are not maintained.

“Despite the fact that many people think we have gotten rid of the oak processionary caterpillar, this is not the case,” the knowledge center stated. “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.”