Mammals
Mole
Talpidae · also called true mole
A mole is a mammal that has committed almost completely to life in the dark. Its hands are turned permanently palm-out for digging, its eyes have shrunk to buried pinpricks, its blood carries a double load of oxygen for stale tunnel air, and it navigates a world it will almost never see by the touch of its nose.
Overview
Moles are the family Talpidae, around 55 species across North America, Europe, and Asia. Most are small, cylindrical, velvet-furred burrowers of moist grassland and woodland soil, though the family also contains the semi-aquatic desmans and some shrew-like surface dwellers. Nearly all feed on earthworms and other soil animals, and a European mole eats close to its own weight every day.
The digging machine
A mole’s forelimbs are rotated so the wide, clawed palms face backward and out, powered by an oversized chest and shoulder skeleton, letting it breaststroke through soil. Digging is one of the most energy-expensive ways to move known, which is why a mole must eat constantly, works in shifts around the clock, and dies quickly if cut off from food. Its haemoglobin and roughly doubled blood volume let it rebreathe the low-oxygen air of a closed burrow.
Reading the dark
Most moles’ pinhead eyes sense only light and dark. Navigation is by touch, through thousands of tiny sensory organs on the snout — a system the star-nosed mole pushes to its limit with a ring of 22 fleshy rays that identify and swallow prey faster than any other mammal can react. Several mole relatives also have venomous saliva for paralysing and storing live worms.
One mole, many molehills
Outside a short breeding season, moles are solitary and territorial. A lawn full of fresh molehills is usually the work of a single animal extending its runs, especially after rain brings worms near the surface, not a colony moving in.
Status
Moles as a family are Not Evaluated. Widespread species such as the European and eastern moles are common and often treated as pests, but several restricted Asian and Japanese moles, and the desmans of Iberia and Russia, are declining from river pollution, dams, and drainage.
Mole: common questions
Are moles blind?
Not quite, though they are close. Most true moles have eyes the size of a pinhead, sometimes covered by a thin layer of skin or fur, and these can register light and dark and perhaps coarse movement but form little or no image. Underground, in permanent darkness, sharp vision has no value and open eyes would just collect dirt and infection, so evolution has reduced them. What a mole relies on instead is an exquisite sense of touch, especially on the snout, along with smell and sensitivity to vibration. The star-nosed mole has taken snout touch to an extreme, with a 22-rayed feeler organ packed with more than 25,000 sensory receptors.
What is the difference between a mole and a shrew or a vole?
They belong to different groups and only the mole is a dedicated digger. Moles, family Talpidae, are heavily built for tunnelling, with huge outward-facing front paws, no visible ears, hidden eyes, and velvety fur that lies in any direction. Shrews are small, fast, sharp-nosed insect hunters related to moles but living mostly on the surface with normal small limbs. Voles are rodents, with chisel-like gnawing front teeth, rounded bodies, small ears, and short tails, and they are vegetarians that eat roots, grass, and bark. A mole in the same lawn as a vole will make raised ridges and volcano-shaped soil heaps, while voles leave surface runways and gnawed plants.
How do moles breathe underground?
The air in a sealed tunnel quickly becomes low in oxygen and heavy with carbon dioxide, which would leave most mammals gasping, but moles are adapted to rebreathe it. Their haemoglobin, the oxygen-carrying molecule in the blood, has a chemistry that lets it pick up oxygen even when there is very little available, and it is less hampered by high carbon dioxide than ours. Moles also carry around twice the blood volume, and therefore twice the oxygen store, of a similar-sized animal that lives above ground. Together these features let a mole keep working hard in air that a surface mammal could not tolerate.
Why is my lawn covered in molehills if moles are solitary?
Because one mole moves a remarkable amount of soil. A single animal maintains a tunnel system that can run for a hundred metres or more, and it pushes the spoil from digging up to the surface at intervals, each push making a fresh heap. A burst of tunnelling after rain, when worms are active near the surface, can throw up a dozen or more molehills across a lawn in a few days, all from the same resident. New mounds appearing after you remove one usually mean the mole is still there and extending its runs, not that a colony has arrived.