Wolverine, the latest movie in the blockbuster X-Men franchise, opens this Friday. The actual wolverine, a furry, dog-size carnivore in the weasel family, is commonly referred to as the strongest mammal in the world, pound for pound. Is it really?
No. No scientific studies have been done on the body strength of wolverines, so claims for their relative mightiness are anecdotal at best. But we do know something about how various mammals stack up when it comes to the force of their bites. In a paper published in 2007, two researchers compared the biting power of 151 species of Carnivora, controlling for body weight. They found a great deal of variation in the data: The most powerful animals were those that feed on large prey or tough, fibrous plants; weaker-jawed critters were more likely to eat insects. The tiger had the strongest bite in absolute terms, but on a pound-for-pound basis, the crown went to the Tasmanian devil. The most powerful bite in North America belongs to the least weasel, less than 1 foot in length and weighing no more than 3 or 4 ounces. * What about the fearsome wolverine? Even among its fellow weasels, its bite force quotient ranks just 20th.
Wolverines are known not only for strength but for ferocity. The idea dates back at least to the early 1900s, when Ernest Thompson Seton, one of the founders of the Boy Scouts of America, wrote: "Picture a weasel … that little demon of destruction, that small atom of insensate courage, that symbol of slaughter, sleeplessness, and tireless, incredible activity—picture that scrap of demoniac fury, multiply that mite some fifty times, and you have the likeness of a wolverine." (According to a wolverine biologist in Montana, myths about the animal's hardy, killer nature stem primarily from "the overactive imagination of north-country trappers.")
The reputation isn't entirely undeserved, though. Wolverines survive in very harsh, Arctic climates and have powerful jaws and teeth designed to crack through frozen meat and bone. They can also be very aggressive when they're hungry, which is often. Whereas a wolf, another tundra animal, can go several days without eating, the wolverine will begin looking for more food just a few hours after finishing a meal. This sometimes leads to confrontations with larger animals: Researchers in Yellowstone found evidence in 2003 that a wolverine had been killed when it tried to drag an elk carcass away from a feeding bear. The wolverine doesn't often hunt big prey, though—it mostly lives on smaller animals like hares and carrion left over after a wolf-pack kill. When it does attack a large animal, like a reindeer or a caribou, it's been known to leap on the prey's back and bite it on the neck.
Bonus Explainer: Does X-Men's Wolverine actually look like a wolverine? Yes. Like his animal namesake, James "Logan" Howlett is compact, hairy, and heavily muscled. Wolverines are famous for their dense, frost-resistant pelts, which are highly valued as parka linings among Arctic people. (The bushy white patches located, masklike, around some wolverines' eyes may correlate with Wolverine's shaggymutton chops.) In North America, wolverines are most commonly found in Canada—Logan's native land—and are solitary beasts, like the superhero. However, male wolverines are oftenpolygamous, whereas Logan is (in the film series, at least) more of a one-womankind of guy. In addition, though the animals have five ivory-colored claws on each paw, they're not fully retractable the way Wolverine's adamantium-fortified ones are.
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Explainer thanks Audrone Biknevicius of Ohio University, Judy Long of the Wolverine Foundation, and Jean-François Robitaille of Laurentian University.
Correction, May 4, 2009: The original version described least weasels as weighing no more than 8 or 9 pounds. That's way off—they rarely weigh more than 3 or 4 ounces. (Return to the corrected sentence.)