Not all bees live in the familiar large wooden boxes or hollow trees associated with honey production. Approximately 70% of the world’s 20,000 bee species are solitary insects that build their nests underground. These ground-nesting bees are important pollinators for both wild plants and cultivated crops. Their presence in a yard or garden indicates a healthy local ecosystem.
Primary Species of Ground-Nesting Bees
Homeowners are most likely to encounter a few major groups of these soil-dwelling insects. Mining bees (Andrena) are common early spring ground-nesters. These bees are medium-sized (5.5 to 15 millimeters long) and are often covered in pale or dark hairs, giving them a fuzzy appearance. They prefer to excavate pencil-sized burrows in bare, sandy, or sparsely vegetated soil.
Digger bees (Anthophora) are robust, chunky insects often resembling small bumble bees. These fast-flying bees (10 to 16 millimeters) are known for their ability to hover and often have distinctive yellow markings on the face, particularly the males. Sweat bees (family Halictidae) are smaller, often just a quarter to three-quarters of an inch long, and exhibit the widest visual range. Many sweat bees are drab black or brown, but some species possess a striking metallic sheen in shades of green, blue, or bronze.
The Architecture of a Solitary Nest
Ground-nesting bees are solitary; each female acts as a single parent, constructing and provisioning her nest. This behavior distinguishes them from social insects like honey bees, which rely on a colony and a queen. A female bee begins by digging a main vertical tunnel into the soil, typically in a dry, well-drained area.
Lateral tunnels branch off from this central shaft, each terminating in a single brood cell. The female provisions each cell with a mixture of pollen and nectar, known as a pollen loaf, which serves as the sole food source for her offspring. She then lays a single egg on the provision mass and seals the cell with a waxy substance secreted from her Dufour’s gland. The young larva consumes the pollen loaf, develops, and pupates within this sealed chamber, often spending the fall and winter underground. New adults emerge the following spring, ready to begin the cycle anew.
Behavior and Sting Risk (Ground Bees vs. Ground Wasps)
A concern for property owners is the perceived danger associated with ground-nesting insects, which often leads to the misidentification of harmless bees. Solitary ground bees are docile, possessing a low sting risk. The female bee is capable of stinging only if she is physically squeezed, stepped on, or roughly handled. Males cannot sting.
This docile nature contrasts sharply with the yellow jacket, a social wasp that nests in the ground. Yellow jackets (Vespula) are aggressive, especially later in the summer and fall, and readily sting to defend their colony. Unlike bees, which are covered in fuzz and fly lazily, yellow jackets have a smooth, shiny appearance, a narrow waist, and dart quickly in and out of their nest entrance. Yellow jackets can sting repeatedly and are responsible for most severe stinging incidents.
Coexisting with Ground Pollinators
Ground-nesting bees are effective pollinators, making them valuable visitors to any landscape. Since their active season as adults is short (often only a few weeks in the spring), lethal management is rarely necessary. For homeowners who find the nesting activity inconvenient, simple, non-chemical methods can encourage the bees to relocate to a less-used area.
Since these bees require dry, bare soil for their burrows, heavy watering of the affected area makes the site unsuitable for nesting, prompting them to move. Covering bare patches of soil with a thick layer of mulch or establishing dense ground cover deters females from digging new nests. These simple actions allow for the conservation of beneficial insects while mitigating their presence in high-traffic zones.