More than 70% of the world’s approximately 20,000 bee species nest in the ground, a fact often surprising to those who primarily think of honeybees and their communal hives. These ground-nesting insects are predominantly solitary bees, meaning they do not live in social colonies with a queen, worker bees, or stored honey to defend. Instead, each female functions as an independent mother, constructing and provisioning a nest for her offspring deep within the soil.
Identifying the Ground-Nesting Bees
The vast majority of ground-nesting bees belong to two major families: Mining Bees (Andrenidae) and Sweat Bees (Halictidae). Mining bees are among the first to emerge in spring, often appearing as small to moderate-sized insects with dark, sometimes banded, bodies and varying amounts of light-colored hair on their thorax. A key feature for the genus Andrena is the presence of facial foveae, distinctive, velvety grooves located near the inner edges of the female’s compound eyes.
Sweat bees, the second-largest family of bees, are incredibly diverse in appearance, ranging from tiny, nondescript brown or black species to those with brilliant metallic coloration. Many sweat bees are a striking metallic green, blue, or purple, and they are typically small, measuring between 3 to 10 millimeters in length. Unlike many other bees, the Halictidae family is best identified by a strongly curved, or arcuate, basal vein on their wings. Neither of these groups has the large pollen baskets seen on the hind legs of honeybees, instead collecting pollen on specialized hairs covering their bodies or legs.
Understanding Solitary Nesting Behavior
The behavior of these solitary bees is focused entirely on maternal care, where each female is solely responsible for creating a secure subterranean nursery. She selects a patch of ground—typically dry, well-drained, sandy soil with sparse vegetation—and excavates a main tunnel using her mandibles and legs. This entrance hole often appears as a small, volcano-like mound of excavated dirt on the soil surface.
The main tunnel extends down before branching off into multiple short side tunnels, each ending in a single brood cell. The female provisions each cell with a mixture of pollen and nectar, known as “bee bread,” which serves as the only food source for the developing larva. Once the egg is laid on this food ball, the mother seals the cell, ensuring the larva has all the resources needed to mature underground until the following year. In some species, like the cellophane bees (Colletes), the female secretes a cellophane-like lining to waterproof the brood cell, protecting the larva from moisture.
Are They Dangerous? Debunking Aggression Myths
A common concern when encountering ground burrows is the potential for aggressive stinging, but solitary ground-nesting bees are overwhelmingly non-aggressive. Since they do not live in a communal hive with thousands of sisters, they have no collective colony to defend. The female’s only defensive concern is her individual nest, making her highly reluctant to sting unless physically threatened.
Stings are rare and usually only occur if a bee is accidentally stepped on or grabbed. For many species, the stinger is either too small to penetrate human skin or the bee lacks the venom to inflict a painful sting. Male ground bees, often seen patrolling a nesting area, do not possess a stinger at all. It is important to distinguish these gentle bees from ground-nesting yellowjackets, which are social, highly aggressive wasps that sting repeatedly to defend their large underground colonies.
Supporting Ground-Nesting Bees in Your Yard
Ground-nesting bees are important native pollinators, and their activity is often temporary, lasting only a few weeks in the spring. Their presence can benefit a yard, as the burrows aerate the soil, improving water and nutrient penetration. The simplest way to encourage a peaceful coexistence is to leave a small patch of ground undisturbed, especially if it is sunny and well-drained.
Homeowners can support these insects by leaving small, bare spots in the yard, avoiding heavy mulch or landscape fabric in these areas. Tilling the soil should also be avoided, as the young bees spend up to 11 months developing underground and are vulnerable to disturbance. If nesting activity occurs in an inconvenient location, the bees can be encouraged to relocate by watering the spot heavily, as they prefer dry soil for nesting.