Moles need both nostrils to locate food underground, in the way that humans see and hear in stereo, according to research reported on Tuesday.
The common mole (Scalopus aquaticus) has tiny eyes tucked between fur and skin and is nearly blind, with small ears attuned only to low frequency sounds.
Curious to understand how the little creature finds food in the dark, biologist Kenneth Catania at Vanderbilt University in Nashville, Tennessee, created a plexiglass chamber in his lab.
The box had 15 holes arranged in a semi-circle in the floor, a different one of which was randomly filled with a tempting piece of earthworm.
The chamber was sealed so that Catania could detect, by minute changes in air pressure, every time the mole sniffed. He also filmed the creatures' movements with a high-speed camera.
"It was amazing," Catania said. "They found the food in less than five seconds and went directly to the right food well almost every time. They have a hyper-sensitive sense of smell."
In the next step, the scientist blocked one of each mole's nostrils with a small polyethylene tube. The animals veered off to the opposite side of whichever nostril was obscured, but eventually found the food.
Finally, Catania inserted small plastic tubes in both nostrils but crossed them over, so that the right nostril was smelling air on the animal's left and the left nostril was smelling air on the animal's right.
With nostrils crossed, the moles crawled backwards and forth, searching for a reward they could smell but, bafflingly, could not locate.
"The fact that moles use stereo odour cues to locate food suggests others mammals that rely heavily on their sense of smell, like dogs and pigs, might also have this ability," Catania said.