New pests may reach Denmark as climate warms

Denmark could see new disease-carrying mosquitoes and ticks establish themselves as the climate grows warmer, according to researchers.

This summer, the oak processionary caterpillar—dubbed “the larva from hell”—has spread across Denmark, leaving many with itching and rashes. But it may not be the only new arrival, says René Bødker, a senior researcher at the University of Copenhagen’s Department of Veterinary and Animal Sciences.

“We’re moving from a Northern Europe where these diseases never existed to a place where we may suddenly see outbreaks,” Bødker told DR. Some species may arrive within decades, while others could be just around the corner, he added.

The Asian tiger mosquito, which can carry dengue fever, has already reached Germany. Though currently too cold for the species in Denmark, warmer temperatures could allow it to establish itself. The mosquito is known for biting aggressively, even in broad daylight—a behavior unfamiliar to Danes, Bødker noted.

Dengue fever typically causes mild flu-like symptoms, but in rare cases, especially in those previously infected, it can lead to severe complications such as internal bleeding and circulatory failure, according to Lasse Vestergaard, a senior physician at Statens Serum Institut (SSI).

Another concern is West Nile virus, which has already been detected in northern Germany. A recent study found that Danish horses have been infected, suggesting the virus may already be present in local mosquitoes. Bødker is currently trapping mosquitoes in Denmark to test for the virus.

West Nile fever often causes no symptoms, but in severe cases—particularly among the elderly or immunocompromised—it can lead to encephalitis. The virus circulates naturally among wild birds but can be transmitted to humans and horses by common mosquitoes.

SSI is closely monitoring both diseases, which were previously considered travel-related but may now emerge locally.