My, What a Big Bite You Have

Little Red Riding Hood may have thought the wolf in grandma’s clothes bared threatening teeth, but—for its size—a least weasel delivers the baddest bite

12-01-2008 // Roger Di Silvestro

AS PREDATORS GO, it is a pretty small animal, topping out at about 8 inches long and 2.5 ounces. In fact, it is the smallest predator in North America and the smallest member of the weasel family, which includes such heavyweights as river otters and wolverines, both running about 20 to 30 pounds. Even its name advertises the fact that it is diminutive—it is called the least weasel. Its closest relatives, the short-tailed and the long-tailed weasels, are almost twice as long and three to six times heavier.

Well, “least” it may be, but it packs one powerful bite. Recent research by Australian and Canadian biologists indicates that the least weasel, ounce for ounce, has the most powerful jaws of any predator in North America. In a study of 151 living carnivores, as well as a few extinct predators, the biologists used a model that allowed them to calculate an animal’s bite power, adjusted for the animal’s size, and assign it a score. A score of more than 100 indicated a bite greater than expected. Among living predators, the African lion scored nicely at 124, the tiger at 130, the giant panda at 151. The least weasel’s score? An impressive 164, second only to the Tasmanian devil, which scored 181 and is adapted to crushing and eating bones. “For its size, the least weasel definitely has the strongest bite of any North American carnivore in our data set, which included most of them,” says Stephen Wroe of the School of Biological Sciences at Australia’s University of Sydney.

Least weasels occur in the northern reaches of Europe and Asia. In North America they range from Alaska across Canada, down into the northern Midwest, around the Great Lakes states and across the Northeast down into North Carolina. With neck, head and shoulders sharing roughly the same girth, they are slender, almost serpentine mammals. They are reddish-brown with white underparts, although in more northerly parts of their range they may, like short- and long-tailed weasels, turn white in winter. Because of this camouflaged coat, the least weasel is called the snow weasel in parts of its European range; in Norway and Sweden it is sometimes called the snow mouse.

Least weasels favor open areas, such as meadows and river bottoms, where they can find two essentials: rodents and water. Scientists suspect the tiny predators need constant access to water and eat as much as 40 percent of their body weight daily. They roam a home range of about 15 to 35 acres, hunting mostly at night. As many as 65 leasts may share a square mile of habitat if food supplies are good; under those conditions, females also can produce two or three litters a year, with three to six young in each. Adults live in dens that may be lined with the fur of their prey. They may also store excess food in their dens. If disturbed near home, least weasels warn off intruders with a chirp, but if the threat heightens, may release a spray of musk from anal scent glands in a manner not unlike that of their more odiferous relatives, the skunks.

Least weasels feed on animals about their own size, such as mice and voles, hunting for the rodents in burrows. And this is where the powerful bite comes into play.

The research by Wroe and his colleagues suggests that in wild dogs, cats and weasels, biting force is an adaptation to large prey. Because least weasels are so small, their tiny prey is relatively large. Consequently, like gray wolves (bite score: 127) killing bison, or African lions taking down Cape buffalo, a least weasel attacking a relatively massive, 4-ounce chipmunk needs powerful jaws for delivering a crushing bite to the windpipe or to the back of the skull.

The link between prey size and predator bite force is so elegantly correlated that Wroe and his colleagues believe studies of bite force in extinct species, based on skull modeling, will help scientists to deduce more accurately the feeding habits of these vanished predators. Which is hardly the least one might expect from the study of least weasels.

Roger Di Silvestro is a National Wildlife senior editor.


WEB EXCLUSIVE

Putting the Bite on Prey Species

For years, traditional wisdom has told us that Africa’s hyenas have the strongest bite of any mammal, stronger even than that of the African lion. But traditional wisdom also once told us that the world was flat. So what about those hyenas and their fabled jaws?

Biting the Dust
A team of Australian and Canadian biologists recently examined the bite power of 151 living carnivores, as well as the jaw force of a few now extinct. The biologists calculated each animal’s bite power relative to the animal’s size, producing a score called the bite force quotient, or BFQ. A score of more than 100 indicated a bite more powerful than expected, and a score of less than 100 indicated the opposite. In general, mammals that prey on relatively large species have relatively powerful bites, compared to other predators.

So what did the study turn up about the hyena’s status as a world champion bone crusher? Prepare to revise the books on these African canines: The spotted hyena scored a BFQ of only 100, chomping down on prey with a maximum force of about 127 pounds. On the other hand, the African lion scored an unexpectedly high BFQ of 124, capable of exerting up to an estimated 296 pounds of pressure when attacking large hoofed species such as Cape buffalo.

Who’d Have Guessed?
One animal that was surprisingly strong was the giant panda. Of the living species tested, its bite ranked number three at 151, a BFQ that represented about 292 pounds of biting pressure. In the panda’s case, bite force has nothing to do with prey size—the panda is one of the rare carnivores that actually feeds mostly on vegetation, in this case bamboo, a fibrously tough plant that demands powerful chewing. (Although the term “carnivore” refers popularly to meat eating, it also is used by scientists in reference to the mammalian order Carnivora, a specific taxonomic group of related species, including felines, canines, bears and others; most are, of course, meat eaters).

Who Has the Strongest Bite of All?
As the National Wildlife story points out, the most powerful bite among living animals belongs to the Tasmanian devil (for more information on this possibly vanishing marsupial, see “Tasmania’s Devil of a Problem,” June/July 2008), a 20-pound predator and scavenger armed with jaws that can exert a force of 94 pounds—yielding a BFQ of 181. But the devil is put in the shade by an extinct carnivorous species. Can you guess which one?

If you said saber-toothed cat, you would be going for the obvious, but you would be wrong. That extinct cat, renowned for fangs up to 7 inches long, was all tooth and no chomp: It was capable of a 219-pound bite force, bone crushing by any standards, but when adjusted for size, yielding a score of only 78—solidly in the underperforming category. Apparently, with those massive canines, the sabertooth could rely on finesse rather than force.

A Bite for the Record Books
The top scorer among the extinct species tested, as well as the top scorer of all, was the marsupial lion, which, being a marsupial, was in fact not really a lion or even a cat. One of the most formidable Australian meat eaters, this stocky creature averaged about 250 pounds and was the only marsupial to be armed with retractable claws, like those of cats. It also bore on each front foot a thumb that was semi-opposable, meaning the animal could actually grab hold of its prey. This creature may at times have stood upright on hind legs and tail, in the manner of a kangaroo. Its jaws bristled with sharp, heavy dentition with which it could deliver a bite of 380 pounds, for a BFQ of 194—a substantial 13 points greater than that of the Tasmanian devil. The marsupial lion went extinct more than 40,000 years ago.—Roger Di Silvestro

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