USAG Ansbach: Understanding the Oak Processionary Moth

By USAG Ansbach Environmental DivisionJune 3, 2025

The caterpillars of the oak processionary moths are a pest that poses a significant threat to humans, animals and oak trees. At USAG Ansbach a total of 450 oaks can be found across the installations.
The caterpillars of the oak processionary moths are a pest that poses a significant threat to humans, animals and oak trees. At USAG Ansbach a total of 450 oaks can be found across the installations.
(Photo Credit: Robert Poorten)
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ANSBACH, Germany — Did you know that the oak (Quercus) is probably one of most important deciduous trees in Central Europe?

It is a habitat for many birds, insects and small mammals. In Germany, more than 10% of forests are made up by different oak species.

At USAG Ansbach a total of 450 oaks can be found across the installations. However, there is one major downside to oaks: the Oak Processionary Moth (Der Eichenpro­zessionsspinner; Thaumetopoea proces­sionea).

The moth occurs in Bavaria on all tree species of the genus oak. It occurs in warm-dry regions and prefers sparse oak forests and individual trees.

The caterpillars of the oak processionary moths are a pest that poses a significant threat to humans, animals and oak trees. They build white, silk-like webs and nests on oak trunks and branches. The caterpil­lars have thousands of tiny hairs that con­tain a protein called thaumetopoein that can cause skin and eye irritation as well as allergic reactions, and is often accom­panied by a severe rash, dizziness, fever, sore throat and less commonly, breathing difficulties in people and animals.

The caterpillars consume leaves, making oak trees vulnerable to diseases and natural disasters like drought and flooding. The very fine hairs can be easily broken and spread further by the wind, typically from May through July. As the thin hair can stick to the underbrush, avoid direct contact with the caterpillar. The toxins can persist in the hair of the shed skin and can still be harmful for months or even years.

Even contact with dead cater­pillars and old nests can be dangerous for humans.

The oak processionary moth was not a pro­blem in the past. Since 1995, however, a strong increase in this formerly rare butter­fly has been observed in Lower and Middle Franconia as well as in western Upper Franconia.

The oak pest is concentrated in the area of the Franconian plateau bet­ween Schweinfurt, Würzburg and Ansbach, where oak trees in public parks and gardens are sometimes heavily infes­ted.

Due to a changing climate, the species is spreading further and further across Germany. Community members should never approach or touch the caterpillars or their nests, as those can contain thousands of shed hairs.

At USAG Ansbach, oak trees are usually marked with red and white tape during the months of May to July and the DPW Pest Control team safely removes any present nests or caterpillars. In case of contact take a shower promptly and wash all clothing. For severe exposure see a doctor.