Press releases

As has been the case nationwide, there have recently been instances of oak processionary moths in the Aachen metropolitan area as well. These have been found on individual trees, including in Brand, Burtscheid, and the Soers. The tree maintenance crew of the Aachen Municipal Services Department identified and removed nests from ten trees. The employees were specially trained for this task and wear full-body disposable suits and hoods with respirators while removing the nests. “The nests are vacuumed from the tree using an industrial vacuum cleaner and a special, airtight bag and are then incinerated,” explains Nino Polaczek-Keilhauer, team leader for tree care at the City Services Department.

The ten cases this year have occurred at previously known locations. “Although we haven’t had any reports of oak processionary moths in the past two years,” says Nino Polaczek-Keilhauer, “but the affected areas are the same as they were three and four years ago. This is because the caterpillars, which are hidden in the tree as eggs starting in late summer, can survive for several years and hatch after a mild winter.”

The oak processionary moth is a species of moth whose caterpillars can pose a threat to human health and also damage the vitality of oak trees. The females lay their eggs in the bark and the layer beneath it in the upper canopy of oak trees, then camouflage them with their own scales. Once the caterpillars hatch in the spring, they feed on the fresh new leaves of the oak trees. As a result, between May and June—until they pupate in July—one frequently sees the species’ characteristic processions in the trees. The caterpillars then retreat to their nests, which are often located beneath thicker branch forks inside the tree, and less commonly on the trunk. What makes the caterpillars dangerous are their stinging hairs, which are only 0.1 to 0.3 millimeters long. These stinging hairs—of which each caterpillar carries about 600,000—contain a stinging toxin and have barbs, allowing them to become embedded in the skin or mucous membranes. This causes itching and rashes of varying severity. Even after the caterpillars pupate, the stinging hairs remain in the nests or on parts of trees, such as the bark, and remain active and toxic for years. In light of climate change and the associated warmer spring months, an expansion of the affected areas cannot be ruled out.

It is important to avoid contact with the caterpillars and their webs and to keep a safe distance from infested trees. An oak processionary moth nest can be recognized by its white-gray web of thick silk threads, which is usually shaped like a hemisphere or a pouch.

Webworm and Oak Processionary Moth

Not all caterpillars in a web are from the oak processionary moth. In the spring, bushes and trees are also covered with webs spun by web moths. The caterpillars of these moths also eat the leaves of trees before they pupate. The webs of these moths are often confused with those of the oak processionary moth; however, the caterpillars of web moths are harmless to humans and animals. One way to distinguish between the webs is that oak processionary moths primarily infest oak trees. Webworms are found on various types of trees and shrubs, such as fruit trees or ornamental shrubs. Sometimes they completely envelop bushes or trees in their webs.

Anyone who discovers a nest in a city tree can report it through the City of Aachen’s call center or online reporting system. For trees on private property, you can contact private tree care companies or pest control services.