Picks from the Past: June 2000

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Eastern Mole, Scalopus aquaticus

Kenneth C. Catania

Eastern Mole, Scalopus aquaticus Unless you make a concerted effort to find them, you are unlikely to encounter star-nosed moles, which spend most of their time mucking about in the muddy soil of wetlands and stream banks. (In fact, it is the wetness of their environment that allows them to sport their extravagant star; moles rub their noses against the soil continually and dirt would quickly damage their delicate fleshy appendages.) But if you live in a house with a yard, you may well be familiar with the tunnels and mounds of some of North America's six other species of mole. The architects themselves seldom emerge above ground, but if you do come across one—unearthed perhaps by a neighborhood dog or deposited on your doorstep by the family cat—you can easily identify it. A mole is a fairly small mammal (about the size of a hamster) with tiny eyes that are often completely hidden by fur, but the dead giveaway is the animal's gigantic, heavily clawed forelimbs, or arms, which are held close to the side of the body.

Huge muscles, connected to massive rectangular humeri (equivalent to your upper arm bones), power the mole's arms. And its clavicle (collarbone), which in most mammals articulates, or connects, with the scapula (shoulder blade), articulates directly with the humerus. These anatomical oddities give the animals their neckless appearance but also power the distinctive breaststroke motion with which the moles dig. (Most other digging animals burrow with their feet positioned below their body.) Moles can generate tremendous force as they tunnel through the soil. In a mole-ridden lawn, you may actually hear the sound of roots breaking as the animals make their inexorable advance through the ground.

Hand of Scalopus aquaticus

Kenneth C. Catania

Moles dig two kinds of tunnel: shallow surface runs, which appear as ridges in the ground, and excavations that may be several feet deep. Ridges form as a mole pushes the overlying soil upward, as if it were traveling under a carpet. If you step on a ridge you will feel yourself sinking into the ground. Soil farther below the surface can't be so easily compressed, so to dig deep, moles have to push soil right out of the tunnels. They do this at the nearest convenient openings, forming the famous mole hills from which mountains are made.