Aplodontia rufa, commonly known as the mountain beaver, is the world's most primitive rodent: elusive, destructive and often mean. But it just loves living in the damp Pacific Northwest.

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When I tell people that the Northwest is the favorite haunt of the mountain beaver, most people scoff, convinced I’m putting them on.

Further description does not help matters.

The mountain beaver is not a beaver.

It most often doesn’t live in the mountains.

It’s extremely basic physically, but has outlasted all its ancestors and is now the lone member of its biological family.

It’s native to the Pacific Northwest and thrives in this area, but very likely you have never seen it, and, like most people, doubt its existence.

Until the trees on the hill above your house fall down.

Then you, like many who came before, will learn that you have been outwitted by Aplodontia rufa, the world’s most primitive rodent.

AT FIRST, MOST people who hear about the mountain beaver think it’s a myth or a joke, like the jackalope or the sea monkey, animals clearly not found in nature.

In fact, the mountain beaver is very much found in nature — but only on the rainy Pacific Coast. Although it ranges from southern British Columbia into California, it’s found most often in Washington and Oregon.

It likes brushy slopes and ravines, particularly those that have been logged or disturbed. And it likes dampness, perhaps because its primitive kidneys don’t work so well and it needs to drink a lot — two-thirds of its body weight daily.

By any count — not that anyone’s actually counted the elusive animals — thousands of mountain beavers are scuttling around Western Washington, as many as two per acre in some areas, biologists say.

But for such a ubiquitous animal, name — or furry face — recognition is near zip.

For fun, try this with friends. Mention of mountain beavers can quickly begin to resemble a Smothers Brothers routine.

“Hey, I think I have mountain beavers.”


“Mountain beavers.”

“What kinda beavers?”

“They’re not beavers.”

“So what are they?

“Mountain beavers.”

“They live in the mountains?”

“No, in the lowlands.”


“In holes.”

“In mole holes?”

“No, in mountain beaver holes.”

“What are they again?”

THE STOUT, STOLID mountain beaver, having survived relatively unchanged for the past 40,000 years or so, is often called a “living fossil.” Every dug-up ancestral bone and skull comes from this narrow coastal strip.

The first mention of this odd little animal, the sole survivor of the most primitive family of rodents, appears to have come in Capt. Meriwether Lewis and Capt. William Clark’s journal of their adventures down the Columbia River to the Pacific Ocean in 1805. At Fort Clatsop, now Astoria, Ore., Clark wrote that the Indians sold him two robes of the skins of “a small animal about the size of a cat.”

“The ears are short, thin and pointed, and covered with a fine short hair, of a uniform reddish brown,” they wrote.

Lewis and Clark had never seen such an animal and questioned the Chinooks about the skins. Told they were “She-wal-lal,” Clark transcribed that as “Sewellel,” and it became one of the animal’s names, along with another Indian name: “Showt’l.”

Later, others determined that Clark mistakenly believed “Sewellel” was the name of the animal, when it was actually the native name for the robe.

Whatever its name, the explorers weren’t going to get rich from its fur. “Captain Lewis offered considerable rewards to the Indians, but was never able to procure one of these animals alive,” the journal concludes.

For years, naturalists went back and forth about what this creature was, exactly: Some kind of beaver? Squirrel? Rabbit? Prairie dog? Muskrat?

Over the years, it’s often been mistaken for other animals. In Oregon, likely because someone thought it was the animal making a particular sound, it was labeled a “boomer.” Others call it a “whistler.” Animal researchers say it chatters, hisses and coughs, but doesn’t boom or whistle.

In the early 1800s, eclectic naturalist Constantine Rafinesque gave the “queer animal” its “rufa” name, Latin for “red-haired.”

In “Animals of the World,” originally published in 1917, H.E. Anthony of the American Museum of Natural History wrote: “On account of certain well-defined peculiarities, the Sewellel, or Showt’l has been placed in a family by itself. It has no close relations in America, but seems to be the sole survivor of an earlier type of rodent.”

ABOUT 13 INCHES long, weighing from two to three pounds, the mountain beaver, with its thick neck and stub for a tail, looks a bit like a fuzzy football with claws.

Perhaps the secret to its success and longevity is that it’s stuck to what works: damp climate, soft ground, nearby water sources and abundant underbrush.

It loves to eat the stuff that grows well here: sword and bracken ferns, rhododendrons, and — this habit earned it the label of “pest” — seedling fir trees. They’re a huge problem for commercial operations, says Georg Ziegltrum, spokesman for the Washington Forest Protection Association. Mountain beavers can kill half the seedlings in areas near burrows, says Weyerhaeuser spokeswoman Shannon Hughes.

The mountain beaver also likes to nibble tree roots, tunnel under trees and roots on slopes, gnaw off small limbs and chew off bark layers all around small adult trees, what biologists call “girdling.”

None of that is good for the trees, or for you, if you need the trees to stay put to stabilize a slope or to make a living or just to look at because you like them.

On the other hand, if you have no precious seedlings, rhododendrons or trees on slopes, but lots of ferns you’re willing to part with, and you like having a little “pet” that lives outdoors, is self-sufficient, determinedly vegetarian and requires little care, a mountain beaver might be just the ticket.

It’s probably better to let it do its own thing, though, because it doesn’t survive well in captivity without special care, and its musky odor and crabby attitude when caught discourage up-close bonding.

Plus, it eats its own soft scat, much like rabbits.

And then there’s the flea.

A. rufa is host to what may be the world’s largest and most primitive flea: Hystrichopsylla schefferi, named — go figure — for local naturalist Theo Scheffer, who, in the early 1900s, measured one clinging to a mountain beaver from Puyallup at .31 inches. Scheffer, in 1929, wrote a detailed monograph on our little friend, the host organism.

Even if none of that is off-putting, A. rufa is hard to find. This is, as one biographer put it, a “little-known animal keeping so closely in its burrow as to be but rarely seen.”

ALWAYS UP FOR a challenge, we took to the woods with a live trap, tramping through blackberries, fallen trees and heavy ground cover.

Mountain beaver burrows are large — 6 to 8 inches across, compared to much smaller mole holes, and clear of dirt. The critter’s tracks are distinctive, closely spaced with long, skinny toes.

In a sloping area thick with sopping-wet underbrush, we located what appeared to be an active burrow, and carefully placed the rectangular cage outside the opening, setting it so that any nibble on the bait (a nice organic apple) would slam shut its doors.

The next day, we returned.

No apple. No mountain beaver.

We repeated the steps for five days.

No apple. No mountain beaver.

We decided that we should keep our day jobs, even though they’re in journalism. Trapping probably pays better, but then, so do lots of things for which we lack the requisite talent.

Turns out there are — no surprise here — tricks to this trapping business.

Without trapping, it’s rare to see a mountain beaver. It is very sensitive to vibration, so walking nearby nearly guarantees it will scurry back into its burrow.

Most man-versus-mountain beaver interactions go something like this: You’re walking along in the woods. All of a sudden, your foot plunges into a hole. You bend down to look. There are many holes. A honeycomb of holes, actually.

Maybe you see some sword ferns piled up outside, or twigs with stripped bark, or some horizontal tooth and claw marks on nearby trees. But, most likely, you’ll never see the actual mountain beaver.

Dan Plute was one of the “lucky” ones. He was cleaning his garage in Redmond one summer evening a few years ago when he noticed a strange, furry lump about 15 feet away on his gravel driveway.

“Whoa, critter!” he said. “What the heck are you?”

Though Plute, 55, grew up in Tukwila, he’d always suspected people were joshing him about mountain beavers. And for sure, he’d never seen this animal.

“He just kept his head down and waddled his way right for me,” recalled Plute, who detailed his experience on a Web site featuring “Mountain Beaver Close Encounters” (www.infowright.com/mtbeaver/closeencounter.html).

When Plute leaned down to look at him, “he looked up, hissed, and lunged at me as well as his tiny legs could,” he recalled. “He was not intimidated by my presence at all.”

Plute snapped some photos, which he later used to discover the identity of “this brave little guy.”

WILDLIFE BIOLOGIST Wendy Arjo, in seven years of studying Aplodontia rufa, has chanced upon one only twice. But working near Montesano with Eric Meister, a contract forester and experienced trapper, she’s acquired enough of them to enroll more than 40 in research studies.

She kept some at the Olympia field station of the USDA’s National Wildlife Research Center for a while to study their eating habits. Most, she released to track their movements and range with radio transmitters on tiny collars.

Collaring a mountain beaver is a two-person job. Meister picks it up — very carefully, because its tiny beaver-like teeth can deliver a worthy chomp — and Arjo tightens its plastic collar.

Fitting a collar around the neck of a football-shaped furball so it will stay put for a year is a fine art. “Not too tight, not too loose,” Arjo says.

When she’s got it just right, they let the critter go.

With the beeps, each transmitting on a different frequency, Arjo tracks each mountain beaver’s comings and goings. Frequently, that required an all-night stakeout to tune in every hour. Then she plotted locations to get an idea of their movements and range.

When a transmitter finally dies, Arjo relocates the animal and uncollars it.

Arjo has gleaned much new information about A. rufa, some of it contradicting long-held lore. For example, she’s learned they can cover two to three acres in a day.

And they’re not strictly nocturnal, as previously thought, but work around the clock, foraging and feeding for an hour or two, then power napping for a couple of hours deep in their tunnels. In that state of torpor, they’re vulnerable to predators, including coyotes, skunks, minks and weasels. “It’s a rough world,” Arjo says.

Perhaps it’s for that reason that the mountain beaver has developed a fiercely territorial and aggressive attitude when cornered.

John Consolini, a professional in the “nuisance wildlife control” business who calculates he’s trapped close to 4,000 mountain beavers over 20 years, recalls catching two young ones. He figured they were siblings, so he put them into the same cage. “They fought to the death, like two pit bulls,” he recalls.

Arjo says mountain beavers are not social at all. Even the male and female don’t get along for any length of time. A quick tryst, and he’s gone for good.

Arjo, who is now working for an environmental consulting firm, is finishing some genetic studies she hopes will settle controversy over the number of mountain beaver sub-species and other genetic-diversity issues.

For a former carnivore biologist who worked with coyotes, studying the mountain beaver has been rewarding. “You’re kind of blazing new territory, which is always fun as a biologist.”

She’s impressed by mountain beavers’ ability to cache food and to deal with their water deficit problem. She’s even impressed with their personal grooming. “I’ve never seen a muddy mountain beaver,” Arjo says.

Each one she’s met has a distinct personality, she notes. “Some are very nice and passive. Some are angry and bite your hand off.” Some, when released, will turn around, defiant, and lunge for her boots, says Arjo, who, like Plute, is clearly amused by such pint-sized pugnaciousness.

Crabby, maybe, but Arjo disagrees with one naturalist’s assertion that the mountain beaver “lacks the intelligence and cunning” of other rodents.

“They’ve survived a long time without having to change,” she says, “so they did something right.”

Carol M. Ostrom is a Pacific Northwest magazine staff writer. Steve Ringman is a Seattle Times staff photographer.