Scapanus latimanus

1. What they did

This is a Mammalian Species account: a standard summary of what was known in 2001 about one species, the broad-footed mole of the western United States and Baja California, Mexico. The authors brought together published work on the mole’s names and subspecies, appearance, body and skull measurements, distribution, fossils, anatomy, reproduction, ecology, behaviour and genetics. The account includes photographs of the mole and its skull and skeleton, and a distribution map of the 12 subspecies.

2. What they found

Appearance and body

• A short, cylindrical body, a long pointed snout, tiny eyes hidden in the fur, no external ears, and short, velvety fur that is dark brown to silvery gray, often with a coppery or brassy wash.
• Very wide, nearly hairless front feet permanently turned outward, with long, wide claws; much smaller hind feet with shorter, more pointed claws.
• Moles in wetter northern and western areas are larger than those in drier southern areas, and males are usually slightly larger than females. Total length is roughly 130 to 190 mm, and adults weighed about 50 to 86 g.
• Each hair has stiff sections that alternate with thin, flat “hinge” sections, so the fur bends easily and the mole can move forward or backward in its tunnels with little friction.

Built for digging

• The collarbone, shoulder blade, upper arm and forearm are short, heavy and highly modified to anchor powerful digging muscles. The front foot cannot be brought under the body.
• An extra sickle-shaped bone widens the hand, and the claws make up more than half the length of the hand.
• The hip and short, fused lower leg bones help the mole brace the hind feet against the tunnel wall while digging or pushing soil.

Where they live

• Moist, fairly rich soils with scant vegetation, from sea level to about 3,000 m. They rarely occur in heavy clay, gravelly or stony soils, and sandy or loose soils are usually not occupied.
• Rocky areas and water are likely barriers, yet one subspecies lives only on Angel Island in San Francisco Bay, and moles have been recorded swimming in rivers.
• Areas that dry out seasonally may be used only for part of the year.

Food and feeding

• The only stomach analysed held 80% snails and 20% beetles.
• In captivity, moles ate on average 70% of their body mass a day in dog food, and 85% when fed earthworms. They scraped food into the mouth with the nose and cleaned earthworms with their front feet, crushing a worm from end to end and back again, which squeezed mud out of its gut.
• Captive moles seemed to need free water.

Breeding

• Probably one litter a year of about 4 young. Young are 72 to 75 mm long at 10 days old and leave the nest at 30 to 35 days.

Predators

• Pine martens in eastern California ate moles except in winter (moles were in 2.6% of droppings). Barn owls, marsh hawks and red-tailed hawks took a few.
• Moles seem most at risk during breeding and when young disperse and leave their burrows.

Behaviour and signs

• Broad-footed moles live underground and are rarely active above ground.
• They make shallow tunnels about 2 cm deep while foraging for insects and worms, pushing up a ridge of soil with many lengthwise cracks (a “mole-run” or surface gallery). These tunnels are used irregularly.
• Deeper tunnels produce volcano-shaped mounds of pushed-up earth, quite different from the crescent-shaped mounds of pocket gophers. The freshest soil is in the core of the mound and rarely shows on the surface, and the mole is never exposed while building it.
• Each burrow system holds only one mole, but a new mole often moves in within 1 or 2 days after the occupant is removed. One mole was caught in a tunnel where a pocket gopher had been caught the day before, suggesting the two may share tunnel systems.
• On smooth concrete one mole ran at 0.6 m per second; in water it swam for 6 minutes without seeming to tire, and did not dive.

Genetics

• 34 chromosomes. Among the moles compared, the broad-footed mole was genetically most similar to Scapanus orarius.

3. What they concluded

As a review, the account does not draw new conclusions. It shows that much of what was known about the broad-footed mole came from anatomy, measurements and a few captive or anecdotal observations, and that some basics rest on very few animals (for example, diet from a single stomach). The authors also note that the narrow pelvis may not be an adaptation to underground life, because some relatives that do not burrow have equally narrow pelvises.

6. Other technologies, skills or innovations

• Earlier studies drawn on in the account used museum specimens, captive feeding trials, analysis of predator droppings and stomach contents, muscle tissue staining, chromosome counts and protein electrophoresis (a genetic method).