THE HEAVY snowfall in central Europe so far this year is making life hard for stone martens. A weasel-like animal, half a metre long with brown fur and a white blaze on its chest, the stone marten has tiny paws too small to keep it suspended on soft snow. It thus has an endearing habit of walking along cross-country ski tracks, where the snow is packed harder. It also has a less endearing habit: gnawing on rubber. Specifically, it likes to crawl into car-engine cavities and chew on the wiring.
As a result, in Germany, car insurance that covers Marderbisse (marten bites) is a must. According to GDV, an insurers’ group, martens were the fourth-leading cause of non-collision auto damage in Germany in 2017. They chewed through €72m ($79m) worth of cables, up from €66m the year before and €28m in 2005.
The rise in marten damage may simply be the consequence of more martens. The population has grown in recent decades, and they are colonising areas from which they had disappeared, such as the eastern Netherlands. Another reason may be declining fear of humans, who create lots of warm, dry spaces like attics that make perfect marten dens.
“They are one of these animals that have become part of the suburban ecosystem,” says Kees Moeliker, director of the Rotterdam Museum of Natural History. He keeps a collection of animals that have died in unusual interactions with humans, including the most dramatic case of marten damage ever. In 2016 one hopped onto an electric transformer at the Large Hadron Collider (LHC) in Switzerland, short-circuiting it and briefly knocking out the particle accelerator. Earlier that year the LHC lost power when a cable was chewed through by an animal which, though rather charred, appears to have been a marten.
What explains the martens’ suicidal tastes? Some biologists note that electrical insulation manufactured in east Asia sometimes contains fish oil. Others think the culprits may be mostly young martens that do not know what is edible; damage tends to peak in spring, when the young are born. Asked for his theory, Mr Moeliker laughs. “This is something we will probably never know, what’s in the head of the marten,” he says.