Oak processionary moth spreads to Scandinavia – authorities respond

The caterpillars prefer to move in procession-like rows along oak bark and produce tens of thousands of tiny stinging hairs per individual, as explained by the Danish Ministry of Nature and Animal Welfare. These hairs "can cause itching, skin rashes and, in rare cases, respiratory difficulties." Even after pupation, empty chrysalis shells and left-behind stinging hairs remain dangerous.

Causes: Climate change and imports from Germany

Experts cite climate change and goods traffic as causes of the spread. "Partly to blame for the spread is a shipment from Germany," the dpa report states. Forest ecologist Hans Peter Raven told the newspaper Politiken: "Der massenhafte Befall dort sei auf die Einfuhr von Eichen aus Deutschland zurückzuführen, auf denen die Falter Eier gelegt hatten." The import of infested oaks is thus considered a concrete trigger for the plague in Odense.

Copenhagen reported the first finds of the oak processionary moth in the city at the beginning of July. Ecologist Mats Wirén from the Swedish city of Malmö, located only about 15 kilometers from Copenhagen, said on Swedish public radio Sveriges Radio that it was very likely the caterpillar would cross the Øresund into Sweden. According to the report, Sweden is preparing for a possible infestation.

Sweden and Norway on heightened alert

Norway, too, is on heightened alert. Anders Endrestøl from the Norwegian Institute for Nature Research (Nina) explained that the animals could reach Norway naturally through the warmer climate or be introduced via imported oaks: "Sie könnten durch natürliche Ausbreitung infolge des wärmeren Klimas hierhergelangen. Sie könnten aber auch mit importierten Eichen eingeschleppt werden." The institute is therefore warning of a possible spread as far as Norway.

In Denmark the caterpillars are colloquially known as "hell caterpillars," a name that reflects the fear inspired by their stinging hairs. The Danish authorities combat the animals and their nests using special adhesive and vacuum cleaners, in order to remove the dangerous hairs as completely as possible.

Countermeasures: Adhesive, vacuum cleaners, and tits

Odense Zoo, which is also affected by the infestation, has temporarily closed parts of its grounds. At the same time, the zoo announced it would put up nesting boxes for tits so that the birds would naturally reduce the caterpillar population. In this way the zoo is combining pest control with a concrete contribution to species conservation.

In Germany the oak processionary moth had already caused great concern during the summer; just a few decades ago it was considered very rare there, but it is now multiplying in large numbers. "Seine Brennhaare sind nun auch in nordischen Ländern gefefürchtet," the dpa report summarizes the development. Propelled by rising temperatures and the trade in oaks, the pest has thus developed into a cross-border problem.

The incidents show how quickly heat-loving species can expand northward and what consequences this has for public health and urban green spaces. Experts see the current spread as further evidence that climate change is fundamentally altering living conditions for pests in Northern Europe. At the same time, the case in Odense illustrates how the import of plant material can unintentionally transport insects over long distances.