The majority of the world’s bee species do not live in large, communal hives like the well-known European honeybee. Approximately 70% of all bee species are solitary insects that build their nests beneath the soil surface. These ground-nesting bees are often overlooked because their activity is concentrated underground, lacking the large, visible colonies associated with social species. Each female constructs and provisions her own nest individually to raise a single generation of offspring.
The Major Families of Ground-Nesting Bees
The vast population of bees that nest underground belongs to several distinct families. One of the largest and most widespread groups is the Mining Bees (Family Andrenidae), which includes over 1,300 species in the genus Andrena alone. Mining bees are typically medium-sized, fuzzy, and brownish-black, and are among the first bees to emerge in early spring to pollinate fruit trees. They are strictly solitary, though they frequently nest in dense aggregations in areas with sunny, bare, or sparsely vegetated soil.
Another prominent family is the Sweat Bees (Family Halictidae), which are often smaller and commonly feature a striking metallic green or copper sheen. While many species are solitary, this family displays a wide range of social behaviors, from solitary nesting to semi-social colonies. They are named for their habit of landing on mammals to lap up perspiration for necessary salts. Digger Bees (Tribe Anthophorini) are also common ground-nesters, typically larger and fuzzier than mining bees.
How Ground Nests Are Constructed
A ground-nesting bee begins by excavating a vertical main tunnel into the soil, often preferring sandy, well-drained locations with minimal vegetation. The entrance is frequently marked by a small, volcano-shaped mound of excavated dirt, known as a tumulus. The female then digs several lateral tunnels branching off the main shaft, each terminating in a single brood cell.
Once the cell is prepared, the female provisions it with a mixture of pollen and nectar, rolled into a ball called “bee bread.” She lays a single egg upon this food source before sealing the cell, often using soil, pebbles, or wood fragments. Some species, such as the Cellophane Bees (Family Colletidae), secrete a glandular substance that dries into a thin, waterproof lining for the brood cell. The young larva develops on the bee bread, overwinters in the sealed cell, and emerges as an adult the following spring.
Understanding Aggression and Sting Risk
The perception of ground-nesting bees as a threat is often exaggerated, as most species are inherently non-aggressive and do not defend their nests. Unlike social insects like honeybees or yellow jackets, solitary ground-nesting bees have no large colony or stored resources to protect. A female will only sting if she is physically trapped, crushed, or severely provoked, such as being accidentally stepped on.
The male bees, which are unable to sting, are often observed flying rapidly near the nest entrances. They patrol the area seeking mates and may appear aggressive due to their erratic flight patterns. Misidentification is common, as highly aggressive, social, ground-nesting yellow jackets are frequently mistaken for docile ground bees. Ground bee nest entrances are usually small, about a quarter-inch wide, contrasting sharply with the constant, busy traffic of a social wasp nest.
Why We Should Protect Ground-Nesting Bees
Ground-nesting bees provide an immense ecological service through their pollination habits, often surpassing the efficiency of managed honeybees for native flora. Many native species are specialists, relying on specific native plants, which ensures a diverse range of plant life is successfully reproduced. Certain ground-nesting bees are also exceptional pollinators for crops such as apples, blueberries, and cherries.
For homeowners, welcoming these bees requires simple habitat management and tolerance, as their active season is typically brief, lasting only a few weeks in the spring. To encourage their presence, avoid the use of broad-spectrum insecticides and leave small, undisturbed patches of bare, sunny soil. The burrows they create also serve a beneficial function by aerating the soil and improving water penetration.