Moles use stereo smelling to hunt prey
London, February 6 : Most mammals, including humans, see in stereo and hear in stereo, but now it's known that a ubiquitous garden critter can smell in stereo too.
A new study has shown definitively that the common mole (Scalopus aquaticus) relies on stereo sniffing to locate its prey.
"I came at this as a skeptic. I thought the moles' nostrils were too close together to effectively detect odor gradients," said Kenneth Catania, the Stevenson Professor of Biological Sciences at Vanderbilt University, who conducted the research.
What he found turned his assumptions upside down and opened new areas for potential future research. "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 said.
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.
As for humans, Catania remains skeptical. "In humans, this is easier to test because you can ask a blindfolded person to tell you which nostril is being stimulated by odors presented with tubes inserted in the nose."
Such studies suggest it is only when an odor is strong enough to irritate the nostril lining that humans can tell which side is most strongly stimulated.
The study was recently published in the journal Nature Communications.