Rewilding Route 1: Moles on the move

By RICK BORCHELT

“Home! That was what they meant, those caressing appeals, those soft touches wafted through the air, those invisible little hands pulling and tugging, all one way!”

So thought Mole, the first character one meets in Kenneth Grahame’s children’s novel, The Wind in the Willows. Mole had clambered aboveground from his earthen tunnels for the first time in his young life, but the scents of home were calling him back underground.

In stereo, as it happens. More on that in a moment. 

While Mole of The Wind in the Willows was a European mole (Talpa europaea), the Eastern moles (Scalopus aquaticus), common across Maryland, might be having the same experience this March. Having spent the winter alone in leaf- or grass-lined nests in a burrow one or two feet deep, our hamster-sized moles are beginning to stir in search of mates. Moles have an exquisite sense of smell that leads them to those potential partners, to the earthworms and grubs that make up the bulk of their diet, and to fresh new lawns and pastures in which to tunnel.

Since our moles seldom venture aboveground, most of us come to know them by the tunnels they dig in search of food and new homesites. The tunnels at the surface can be simply long, narrow and meandering raised bumps in a yard or field, or they can be a series of fresh soil mounds dotting the lawn (the source of the term molehill). Moles are prodigious diggers; in loose soil, they can tunnel almost 20 feet in an hour. These tunnels serve as mole highways, certainly, but they are also effective earthworm and grub traps as helpless prey fall into the waiting chasms.  

Moles are supremely adapted for this subterranean lifestyle. They have enormous, spade-like front feet angled outward from their body that make digging fast and efficient. They have no eyes to speak of, so there’s no chance of getting dirt in them, and their ears are tiny and covered with fur. The fur itself is short, soft and velvety, and can be brushed in any direction, offering little resistance to the soil. When a mole wants to turn around in a tunnel, it simply does a quick somersault and reverses direction.

Their frenetic tunneling keeps moles alive. They are voracious eaters and if deprived of food typically expire in less than a day. They eat their weight in earthworms and insects almost daily, a rate of consumption that totals 50 pounds or more a year. To keep up this feeding pace they seldom sleep, taking short naps every couple of hours before returning to their tunneling.  

How moles find their prey in these earthen runs — in the darkness and with limited hearing — was long a mystery to naturalists. Scientists at Vanderbilt University have discovered one of the  moles’ secret weapons: They can smell in stereo. Each nostril operates independently, with the two inputs giving a very precise signal to the whereabouts of a prey item. Moles whose noses were experimentally clogged couldn’t tell there was any food around at all; if only one nostril was clogged, they could tell there was food but couldn’t find it.  

Another adaptation to their subterranean lifestyle: Moles also have a high tolerance for breathing in carbon dioxide at levels that would prove fatal to most mammals.

Eastern moles aren’t the only moles that call our region home. Star-nosed moles (Conduylura cristata) are not as common or widespread as Eastern moles, but can be found in many places across Maryland where there is water and mostly sandy soil.. They have a longer tail than Eastern moles do, and their eyes, while still quite tiny, are at least functional.  

Impressive as the Eastern mole’s olfactory senses are, star-nosed moles put them to shame. Around their nose is a ring of super-sensitive, fleshy appendages packed with epidermal receptors that collectively are called the Eimer’s organ. With this adaptation, it appears they can even smell underwater.

While Eastern moles carry the species name aquaticus, they’re almost entirely terrestrial, though they can swim well if pressed. Star-nosed moles, on the other hand, spend as much time in the water as in their tunnels. On land, they hunt the same prey as Eastern moles but supplement their diet with small fish, tadpoles and other foodstuffs hunted underwater. A star-nosed mole will locate aquatic prey partly by searching around for it using its Eimer’s organ. But its real trick is breathing bubbles out through its nostrils, then breathing the bubbles back in. Those incoming bubbles carry scent molecules  that the mole sniffs in stereo just like its landlubber cousins do. (Follow this link to watch this watery spectacle in a National Science Foundation video).

Moles seldom get the respect they deserve. Our moles are far more beneficial than they are pestilent, both because they eat underground insect pests and because they aerate the soil with their tunneling tactics.  

But golf course managers and lawn lovers routinely make mountains out of the molehills they discover, railing against the unsightly runs and fresh piles of dirt. Gardeners wage war on them unjustly in the belief that moles tunnel into vegetable patches in search of carrots, potatoes and radishes. The real garden culprit, though, is another small mammal, the vole, that uses the extensive mole superhighways to navigate to the vegetarian diet it craves.  

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Rick Borchelt is a botanist and science writer who gardens and writes about natural history at his home in College Park. Reach him with questions about this column at rborchelt@gmail.com.