Eastern mole (Scalopus aquaticus)
Humans and most other mammals can see and hear in stereo, but now it’s known that a ubiquitous garden critter can smell in stereo too.
The super smeller is the common mole, according to a paper in the journal Nature Communications. This is the same animal that might be out in your lawn and garden right this very minute, digging holes and searching for something tasty to eat. We don’t often get to see moles up close, but as you can tell from the photo (above), it’s all about the nose.
Stereo smelling means that each nostril takes in different odors, with the brain recognizing those differences. The discovery is a first, since no mammals were thought to have this ability.
“I came at this as a skeptic,” neuroscientist Kenneth Catania of Vanderbilt University was quoted as saying in a press release. “I thought the moles’ nostrils were too close together to effectively detect odor gradients. The fact that moles use stereo odor cues to locate food suggests other mammals that rely heavily on their sense of smell, like dogs and pigs, might also have this ability.”
Catania’s study created a radial arena with food wells spaced around a 180-degree circle with the entrance for the mole in the center. He then ran a number of trials with a mole food fave — pieces of earthworm — placed randomly in different wells. The chamber was temporarily sealed so Catania could detect each time the mole sniffed by the change in air pressure.
“It was amazing,” he said. ”They found the food in less than five seconds and went to the right food well almost every time. They have a hyper-sensitive sense of smell.”
He noticed a pattern. When a mole would enter a chamber, it moved its nose back and forth as it sniffed, but then the mole seemed to zero in on the food source, moving in a direct path. That’s when the “stereo sniffing” idea dawned on Catania.
When the moles’ left nostrils were blocked, the animals’ paths consistently veered off to the right. When their right nostrils were blocked, they consistently veered to the left. They still found the food, but it took a much longer time.
Catania conducted further tests, inserting plastic tubes in both of the moles’ nostrils. He crossed these tubes such that the right nostril was sniffing air on the animal’s left and the left nostril was sniffing air on the animal’s right. When their nostrils were crossed in this fashion, the animals searched back and forth and frequently could not find the food at all.
The conclusion? Moles indeed smell in stereo, as he suspected.
Catania said he doubts humans have this ability.
Tests for this aren’t difficult to do on humans, he said. “You can ask a blindfolded person to tell you which nostril is being stimulated by odors presented with tubes inserted in the nose.”
These investigations suggest only when a strong odor irritates the nostril lining (such as whiffing a cut onion) can humans can tell which side is most strongly stimulated.
(Image: Kenneth Catania)