Moose flies invade northern Finland as populations rise in Meri-Lappi

To escape the torment of moose flies, outdoor enthusiasts should choose their destinations well north of the Arctic Circle. These pesky insects can be found as far south as Rovaniemi, and their northern spread continues. In Meri-Lappi, the population of moose flies has become alarmingly high, as hunter Juha Mäkimartti is painfully aware. “When I remove them from my body in the evenings before sauna, I look up and wonder why such creatures exist,” he noted. Some of Mäkimartti’s acquaintances have stopped venturing into the woods during the autumn weeks.

Specialist researcher Juho Matala from the Natural Resources Institute has also experienced this change firsthand in Keminmaa. He explains that 15 years ago, there were no moose flies in Meri-Lappi. “The population has clearly increased and spread from the inland areas to riverbanks and coastal regions. Each time I go into the woods this autumn, I encounter them,” he shared.

A decade ago, it was believed that the spread of moose flies would stop at the reindeer herding boundary. However, it was later discovered that they can also breed in reindeer, although not as prolifically as in moose, where populations can reach into the tens of thousands. Research has indicated that the deworming medication ivermectin, used during reindeer sorting, can reduce moose fly populations by preventing their eggs from developing into insects.

Rovaniemi’s veterinarian Linda Mononen confirmed these findings, noting that moose flies have been found on reindeer in the past two years. While moose flies prefer moose, their spread ultimately depends on moose population density. Despite a lower moose population in northern Lapland compared to the south, Matala does not believe the area will entirely escape this nuisance, especially as reindeer also serve as host animals.

The warm autumn weather may extend the flight season for these insects, which typically cease flying when temperatures drop below freezing. Scientist Juho Matala suggests that ongoing climate change could further lengthen this period, as warmer summers may accelerate their development.