Moles smell in stereo!

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Dear Why Files

Dear Why Files:

I don’t get it. I’m a plain ol’ mole, and my self-image is in the toilet. Sure, I dig a lot of holes as I chase insects and earthworms. People blame me for wrecking their silly lawns, but that’s nothing compared to a squirrel in the attic or a Canada goose laying “cigars” on the grass. And I’m no rabid dog: I don’t make people sick. And I can’t remember the last time anybody asked to take my photo! Even though we live underfoot, we still have feelings!

–Depressed Digger

Dear Depressed Digger

I sympathize. Sure, moles are short on charisma, and that all-subterranean-all-the-time lifestyle is a real recipe for cabin fever.

But you’re making a mountain from a molehill! I’ve just heard from an admirer in Tennessee who thinks you can do what nobody else can: smell in stereo! Fifty-plus years after record companies began selling discs that deliver a different sound to each speaker, and 500 million years (just wild-guessing now) after animals began using two eyes to get a better picture of their environs, Kenneth Catania, a professor of biology at Vanderbilt University, says you may be the only animal proven to smell in stereo.


Large claws of mole splay grass as it pokes out of hole in ground

The eastern mole (Scalopus aquaticus) lives entirely underground, devouring earthworms that it detects with a super schnozzola.

You, the innocent and invisible common mole, AKA the eastern mole. Feeling better already?

Separate, but equal?

The idea that the sensory nerves behind each nostril may deliver different information to the brain “has been out there, people have been curious for a long time,” Catania says. “Paired eyes and ears are important for stereo vision, depth perception, and sound localization, so it’s natural to wonder” if having two nostrils would help locate the source of an odor.

But Catania says he started out “a big skeptic. I thought the nostrils [in the common mole] were so close together, what are the chances they could localize a smell?”

Catania says he’d been looking at the starnose mole “which has an incredible sense of touch” (though evolution has given it a rather strange mug). He said you, the common mole, “have the worst sense of touch among the mole species,” so he was sure you would be a fumbling idiot when you had to search for food.

Instead, Catania says, you “went straight toward the food. I am not sure there is any study in mammals that shows a better localization of an odorant” in a test chamber.

Everybody gets to be a champion!

Furry mole head with several pink tendrils extending from nose pokes out of hole in ground

The star-nose mole uses its exquisite sense of touch to find food.

Catania was smart enough to wonder if common moles could be smelling in stereo. “It was very hard to explain how they doing so well otherwise,” he says. Knowing that you “would do anything if is there is an earthworm at the end of it,” he put you into a test chamber with a bit of earthworm as bait, and counted how long it took you to find it.

Double-click on movie to watch a double-speed image of a common mole finding bait in the test chamber; followed by a mole with one nostril blocked.
Courtesy Kenneth Catania, Vanderbilt University

Immediately, you started wriggling your nose and moving around, kinda like people try to locate a “present” from their dog.

And in as little as five seconds of frantic sniffing, you found the bait.

Then the fun began. When Catania plugged your right nostril, you following the stronger scent on the right, veered too far left, but eventually homed in on your reward. But when he hooked your sniffer up to a crisscross pipe, so each nostril smelled the opposite side, you were bewildered and never found the bait.

The discovery of stereo smelling is sexy, but Catania notices that you start out using the more common sniff-move-sniff technique, and then switch to stereo-smelling when you got closer to the pay dirt.

No offense, but we asked Catania why this mattered. He admitted that “a lot of it is just inherently cool. But I’m always amazed at what animals can do. I will be studying them for one reason, and they tell me something completely different. When I went into this, I thought the common mole would have poor foraging ability due to its poor sense of touch, but they were off-the-scale good in another way.”

So chin up, Depressed Digger: As far as your self-image is concerned, there’s light at the end of the tunnel! Not that you can actually see it, unfortunately…

— David J. (Not Ann Landers) Tenenbaum


Terry Devitt, editor; Emily Eggleston, project assistant; S.V. Medaris, designer/illustrator; David J. Tenenbaum, feature writer; Amy Toburen, content development executive