Finding unexpected mounds of dirt in a yard often signals the presence of subterranean wildlife. These soil disturbances are a byproduct of tunneling, as creatures excavate material to build or maintain their underground homes and foraging routes. While many small animals move soil, the characteristics of the resulting pile—its shape, size, and the location of any entrance—provide distinct clues about the unseen resident below. Differentiating between the various types of earthworks allows for a more accurate assessment of the activity occurring just beneath the lawn’s surface.
Moles: The Volcanic Mound Builders
Moles are insectivores that spend nearly their entire lives underground, constantly digging to hunt for earthworms and soil-dwelling insects. These animals create two types of tunnels: shallow, temporary hunting runs visible as raised ridges on the surface, and deeper, more permanent main runways. The digging process forces excess soil upward through vertical tunnels, forming the characteristic molehill.
The mole’s mound is distinctly conical or “volcanic” in shape, rising steeply to a peak. A significant identifying feature is the lack of an obvious central entrance hole, because the soil is pushed up from below, effectively sealing the point of entry. The soil in these mounds is typically loose, finely textured, and clumped together.
Moles have a high metabolic rate, requiring them to consume a large volume of food daily, which drives their constant tunneling. Their primary diet consists of earthworms. The appearance of these mounds is a direct result of the mole’s powerful, spade-like forefeet, which are adapted for pushing soil out of the way as they search for prey.
Pocket Gophers: Fan-Shaped Earthworks
Pocket gophers are burrowing rodents that pose a problem because of their diet of plant roots, bulbs, and vegetation. Gophers are herbivores, and their tunneling is primarily for creating living spaces and finding plant material. They use external, fur-lined cheek pouches to carry food back to underground storage chambers, which is how they earned their name.
Gopher mounds are easily distinguished from molehills by their shape, which is typically a flattened fan or crescent. The soil is pushed out of a lateral tunnel and forms a pile that is often lower and wider than a mole’s mound. The most definitive sign of a gopher is the presence of a sealed entrance, or “soil plug,” located off-center on the mound’s flat side.
This plug seals the opening to the burrow system, which is a defensive behavior to protect the gopher from predators and to maintain a consistent environment. Gopher burrow systems are complex, featuring a main runway that can be 4 to 18 inches below the surface, with side tunnels leading to food caches and nesting chambers.
Other Animals Leaving Dirt Piles
While moles and gophers create the most significant soil mounds, smaller excavations from insects and other burrowing animals are also common. Ground-nesting wasps, such as cicada killers, create small, neat piles of excavated dirt with a distinct, quarter-sized hole in the center. These solitary wasps prefer dry, sandy soil, and the small spoil pile is minimal compared to the large mounds of mammals.
Ant colonies leave small, granular piles of fine soil particles. These piles are usually low, wide, and appear to be made of sifted earth or sand excavated from the colony’s central shaft. The presence of many tiny, busy insects around the pile’s entrance hole is the definitive marker.
In wet or saturated areas, burrowing crayfish may be the culprit, creating unique structures known as “mud chimneys.” These are columnar, smokestack-like mounds of mud pellets, often rising three to eight inches above the soil surface. The crayfish stacks small mud balls to form the chimney, which has a single, large opening at the top and is dug down to the water table.
Quick Reference Guide for Identification
Identifying the animal by the mound requires a close look at three specific characteristics. The shape of the pile is the first clue: a molehill is a symmetrical, rounded cone, while a gopher mound is an asymmetrical fan or crescent shape. Crayfish chimneys are columnar mud tubes, and wasp mounds are small, low circles of dirt.
The location of the entrance hole is the second defining factor. A molehill generally has no visible entrance hole at the peak because the tunnel is plugged from below with soil. Conversely, a gopher mound features a distinct, sealed plug of dirt located off-center on the mound’s edge. Insect mounds, such as those made by ants and ground wasps, have an open, distinct entrance hole in the center of the small pile.
The composition and texture of the soil also offer insight. Mole and gopher mounds are made of clumped soil excavated from deeper layers. Ant mounds are composed of very fine, granular soil particles. Crayfish chimneys are unique because they are constructed of mud pellets, indicating they are found in areas with a high water table and saturated soil.