BERLIN—Ever wondered what kind of weasel would vandalize a perfectly good car left outside at night?
Germany has the answer: Its technical name is the stone marten. This sharp-toothed critter has a habit of squeezing into the innards of parked cars and feasting on plastic hoses and tubes. And Germany’s marten population is exploding.
Weasel damage is the fourth most frequent cause for non-collision auto insurance claims in Germany. Last year, drivers here filed 198,000 claims for weasel-inflicted damage, a 42% increase since 2005. And that probably underestimates the carnage.
“We only have data from those insurers that offer a weasel policy,” said Henning Engelage, a spokesman for the insurers’ federation.
While other Europeans may dismiss weasel attacks as a mere annoyance, no one messes with a German’s car without consequences, says Michael Schönthal, owner of MS MarderSicher GmbH, a maker of popular weasel deterrent systems.
Which is why the German auto industry has declared war on the weasel. Like any war, it starts with getting to know the enemy.
Biologist Susann Parlow at the Otter Center, where auto parts are tested against weasels. PHOTO: PHILIPP SCHULZE/DPA/ZUMA PRESS
“The stone marten is an intelligent animal,” says Susann Parlow, a biologist at the Otter Center, a conservation center, in Hankensbüttel, about 27 miles north of Volkswagen AG’s Wolfsburg factory. The lone, ferociously territorial creature “understands that there is a rich buffet on offer in human civilization.” It rifles through garbage and steals eggs. Auto parts aren’t technically edible; they seem to send the stone marten into a rage.
Ms. Parlow conducts research for auto makers, suppliers, and other industries to develop more effective anti-weasel defenses.
“They come to us with hoses they have developed and want to know if they are safe,” she says, pointing to a pile of boards in her lab, each with a row of hoses tacked to them, from past research. Most are torn, the telltale sign of a weasel feeding frenzy.
Weasel vandalism reached epidemic proportions only recently, but has been a sporadic problem for decades. In 1979, Ruedi Muggler, a game commissioner in Winterthur, Switzerland, posited the existence of a new “auto weasel” after catching one red-pawed in the first documented ferret car invasion.
Similar incidents followed—in southern Bavaria in 1979, Stuttgart in 1983, and Berlin in 1986.
The German Automobile Club warned that German cars appeared especially delectable to the animals. Worried that fear of the weasel would drive customers to seemingly inedible foreign brands, Audi AG, the luxury car maker owned by Volkswagen AG; and Mercedes-Benz, owned by Daimler AG, hired a biologist in 1982 to get to the bottom of the problem.
Karl Kugelschafter, now 64, interviewed hundreds of victims, locked up luxury cars in cages and watched as the weasels ripped them to shreds.
“They go absolutely insane and tear everything apart,” said Mr. Kugelschafter, who today is better known as the inventor of a groundbreaking method of counting bats.
He rejected the mutation theory, settling instead on biology and economics. By the 1950s, stone marten populations had been decimated in Europe due to high demand for pelts in the U.S. When that fashion passed, populations began to recover, just as car ownership was exploding in Germany.
The early days of the war on weasels were frustrating. Sprays made from dog or bear urine didn’t work.
Then, Manfred Gutjahr, a senior research executive at Daimler, took Mr. Kugelschafter’s research and launched the Manhattan Project of Germany’s weasel defense. His key legacy was the Weidenzaunprinzip, or “pasture fence principle”: an electric fence woven around the engine to zap the critters. In 1985, Mr. Gutjahr and his team registered the first patent for a weasel defense system that remains the anti-weasel weapon of choice today.
Mercedes-Benz once used the device in an advertisement for a new electric version of its A-Class. A wily weasel crawls into the car’s engine and is repelled by a stiff electric shock, followed by the message: “The electric A-Class, Innovation with Power.”
Audi, in a bit of territorial marking of its own, advertises an optional Marderabwehrsystem, or Weasel Defense System, with the slogan: “My Audi, My Territory.” It sells the system for around €205, or $228, plus installation costs. The company continues to research the threat. In 2014, engineers conducted their own zoological experiment, installing tiny cameras inside an engine to observe the weasel at work.
Systems based on the pasture fence model are relatively expensive, costing $500 on average. And with the weasel population fast rising, smaller companies have come up with inexpensive alternatives.
Weasel repellent spray retails for around $20 a can. There are dozens of products online in the German Amazon store with names like Marderschreck (Scourge of the Weasel), MartenEX, or Dr. Stähler’s Marderabwehr Spray. Some are biodegradable while others promise to also repel raccoons.
There are mats and netting that can be attached to the underside of the engine, and mechanical devices such as decoy cables that can be hooked up to a battery source to shock the animals when they bite.
At the more sophisticated end, K&K Handelsgesellschaft mbH, has developed a weasel-defense array of six ultrasound speakers coupled with high-voltage electricity. The speakers send ultrasound bursts that are inaudible to humans but allegedly unbearable to weasels.
Should a brave or deaf weasel nevertheless climb on board and touch the speakers, it gets hit with a 300 volt shock that K&K claims will “spoil the weasel’s fun playing in the engine.”