Oak processionary moth spreads in Denmark despite control efforts

A daycare centre in Odense has been temporarily closed and public access restricted on several trails after the oak processionary moth, known locally as the “larva from hell,” continued to spread despite extensive control measures, according to a report by DR.

The caterpillars, covered in over 60,000 microscopic hairs that can cause rashes and respiratory issues, have proven impossible to eradicate, both Odense Municipality and experts confirm.

Last year, the municipality spent two million kroner removing 2,500 nests, treating trees with chemicals, and vacuuming up larvae. Yet the infestation persists, forcing the closure of Ørbækparken Børnehus and warnings against using three public paths where outbreaks have been reported.

Mathias Just Justesen, an associate professor at the University of Copenhagen’s Department of Geosciences and Natural Resource Management, stated that eradication is not feasible. “They will not get rid of it in Odense. That is certain,” he said.

The species, believed to have entered Denmark via imported trees, is also spreading naturally. Just Justesen noted that a colleague recently observed the moth about 100 kilometres south of the Danish-German border. “It can move five to ten kilometres a year on its own. In about ten years, it might reach the border,” he added.

With no national authority currently responsible for combating the pest, Just Justesen warned that responsibility falls unevenly on individual municipalities where outbreaks occur. Last year, after the moth was detected in three municipalities, calls were made for a national action plan.

Nature and animal welfare minister Christian Rabjerg Madsen (S) told DR he takes the situation seriously and has instructed his ministry to coordinate a response involving the Agency for Green Transition and Water Environment, the Danish Health Authority, the Environmental Protection Agency, and KL (Local Government Denmark).

Odense Municipality will now prioritise control efforts in high-traffic areas such as schools and daycare centres, using methods like vacuuming larvae from oak trunks and heat treatment. Elsewhere, warning signs will be posted. Residents are urged to report sightings but not to attempt removal themselves.

Just Justesen advised the public to treat the caterpillars like other hazards: “Just as you know not to touch an adder, you’ll need to know—if you live in Odense now, but this could also apply to Copenhageners and Jutlanders—that if you encounter the larva or signs of its presence, you should stay away.”