Many insect species spend significant portions of their lives beneath the ground. This subterranean existence is a common behavior, allowing them to interact deeply with their environment. The ground serves as a dynamic habitat, supporting a hidden world of insect activity. Many insects rely on burrowing for survival and reproduction.
Why Insects Burrow
Burrowing offers insects several biological advantages for survival. A primary reason for tunneling is to find shelter from external threats. The soil protects them from predators and harsh environmental conditions like extreme temperatures, heavy rainfall, or desiccation during dry spells.
The underground environment also serves as a crucial space for reproduction and nesting. Many insects create subterranean chambers to lay eggs, providing a safe haven for their offspring. Some, like solitary wasps, provision these nests with food for their developing young. The ground also offers a consistent food source for certain species, providing access to roots, tubers, or decaying organic matter. For insects undergoing complete metamorphosis, burrows act as secure pupation sites, allowing them to transform safely.
Common Burrowing Insects
Many insect species commonly burrow, each with distinctive habits.
Cicada Killers
These large solitary wasps create substantial burrows. Tunnels can extend 10 to 20 inches deep, sometimes reaching up to four feet, with an entrance typically around half an inch in diameter. The female cicada killer excavates these burrows, which may feature branched tunnels and multiple globular cells, using her jaws and hind legs to push out soil. This often results in a U-shaped spoil pile at the entrance. She then provisions these cells with paralyzed cicadas for her larvae.
Ground Bees
A diverse group of solitary bees, ground bees frequently burrow for nesting. About 70% of bee species worldwide are ground nesters, preferring dry, loose, or sandy soil with sparse vegetation. They create small, neat holes, often 0.25 to 0.5 inches in diameter, sometimes accompanied by a small mound of excavated dirt around the opening. Each female bee digs her own burrow, up to three feet deep, provisioning individual cells with pollen and nectar for her offspring.
Ants
Ants are known for their extensive underground colonies, which vary greatly in complexity and size depending on the species. Their nests are intricate networks of interconnected tunnels and chambers. These subterranean structures can range from shallow tunnels a few centimeters deep to elaborate systems extending several meters underground, with various chambers dedicated to food storage, nurseries for young, and resting areas. Ants use their mandibles to excavate soil, transporting small clumps to the surface to form the familiar ant hills, which serve as entrances.
Mole Crickets
These insects are highly adapted for subterranean life. They possess distinctive shovel-like forelegs, which they use to dig tunnels just beneath the soil surface. Their burrowing activity often results in raised ridges or mounds in lawns, as they push soil aside. Mole crickets spend most of their lives underground, using their tunnels for feeding on roots, escaping predators, attracting mates, and raising their young.
Beetle Grubs
The larval stages of certain beetles, commonly known as grubs, also inhabit the soil and create burrows. June beetle grubs, for instance, are C-shaped, cream-colored larvae that feed on plant roots underground. As they move through the soil, they create tunnels. Their burrowing can lead to the loosening of soil and dislodge plants or create small mounds of soil, particularly when they are preparing to pupate.
Identifying Burrowing Activity
Identifying insect burrowing involves observing characteristics of the holes and surrounding soil. Burrow openings vary considerably in size and shape, from pinprick-sized to thumb-sized, and can be round or irregular. Some burrows remain open, while others might be plugged with soil or debris.
Soil displacement around the entrance is another key indicator. Neat, crescent-shaped mounds of excavated soil often accompany cicada killer burrows. Ants typically create scattered piles of granular dirt, forming the classic ant hill. Mole crickets produce raised ridges or small, indistinct mounds as they tunnel just below the surface, particularly in sandy soils. These subtle changes in soil topography signal underground activity.
The location and context of the burrows provide additional diagnostic information. Burrows might be found in bare soil, under rocks, near plants, or in lawns, with specific insects preferring certain soil types or vegetation densities. Indirect signs of burrowing, such as damaged vegetation near the holes, can also be present if insects feed on roots, as seen with some beetle grubs. Observing the presence or absence of active insects near the openings can further aid in identification.