A molehill (or mole-hill) is a conical mound of loose soil raised by small burrowing mammals, including moles, but also similar animals such as mole-rats, marsupial moles and voles. They are often the only sign to indicate the presence of the animal.
Molehills are waste material from digging or repairing burrows, and so are usually found where the animal is establishing new burrows, or where existing ones are damaged (for example by the weight of grazing livestock). Where moles burrow beneath the roots of trees or shrubs, the roots support the tunnel, and molehills are less common, and so even a dense population of the animals may be inconspicuous in these places.
Molehills commonly occur in lines along the route of the burrow, but in some cases they may not be directly above the burrow itself but at the ends of short side-tunnels.
Molehills have an important benefit to soil by aerating and tilling it, adding to its fertility. They may however cause damage to gardens and areas of grass (such as a golf course), and in 1702, William III of England died from pneumonia after his horse tripped on a molehill. Such accidents, however, are quite rare.