Most people associate bees with large, social colonies housed in wooden boxes or hollow trees, but this image represents only a small fraction of the global bee population. A significant number of native bee species, perhaps up to 70%, are solitary insects that establish their nests below the surface of the soil. These ground-nesting bees are highly efficient pollinators. They are often incorrectly identified as aggressive stinging insects due to the small mounds they create in lawns or garden beds. Understanding these subterranean residents is key to appreciating their ecological role and mitigating homeowner concerns.
Identifying Ground-Nesting Bees
The most common ground-nesting bees in North America belong to the families Andrenidae (Mining Bees) and Halictidae (Sweat Bees), alongside certain species of Apidae known as Digger Bees. Mining Bees (genus Andrena) are among the earliest to emerge in the spring, often foraging on fruit trees and early-blooming flowers. Sweat Bees (Halictidae) are generally smaller and may exhibit metallic colors, ranging from bright green to bronze. They are frequently attracted to perspiration, which gives them their common name.
The physical signs of ground bee nesting are typically small, volcano-shaped piles of excavated soil scattered across patchy or dry lawn. These mounds are usually only a few inches wide and feature a single, distinct central opening, which is the main entrance to the nest tunnel. This differs from the entrance to a social wasp nest, such as those of yellowjackets. Yellowjacket entrances often appear as a less defined, wide hole or fissure in the ground, with many workers rapidly flying in and out. Yellowjackets do not create the neat, conical soil mounds characteristic of solitary bees.
Solitary Nature and Nest Construction
Unlike honeybees, which maintain a complex social structure with a queen, workers, and drones, ground bees are predominantly solitary. Each female operates independently, solely responsible for constructing, provisioning, and safeguarding her own nest. She does not share resources or duties with other females. While many solitary bees may nest in close proximity, forming dense aggregations, they do not function as a cohesive colony.
Nest construction begins with the female digging a main vertical tunnel that can extend a foot or more into the soil, depending on the species and soil type. Off the main shaft, she excavates several lateral tunnels, each terminating in a single brood cell. Within each cell, the female deposits a mass of pollen mixed with nectar, forming a specialized food source called a pollen loaf. She then lays a single egg on this provision, seals the cell, and moves on, ensuring the larva has a protected, ready-made meal upon hatching.
Understanding Aggression and Stinging Risk
The solitary lifestyle of ground bees translates into a minimal level of aggression and a very low stinging risk for humans and pets. Because the female bee does not have a large, perennial colony, stored honey, or sister workers to protect, she lacks the defensive instinct found in social insects. A ground bee will only sting if she is physically trapped, such as being accidentally stepped on or grabbed.
Disturbance of the nest entrance does not typically provoke an attack from solitary bees, as the female is focused on her individual tunneling and provisioning tasks. This contrasts sharply with ground-nesting social wasps like yellowjackets, which aggressively swarm and repeatedly sting to defend their large colony when the entrance hole is disturbed. The stingers of most solitary ground bee species are smaller than those of honeybees and are less potent, posing little threat unless a person has a severe allergy.
Coexisting with Ground Bees
Given their non-aggressive nature and status as native pollinators, the best approach to managing ground bees is typically tolerance and non-lethal intervention. Ground-nesting bees are most active for a short period, usually a four-to-six-week window in the spring or early summer. The nests are not reused in subsequent years. During their active season, marking off the nesting area with small flags or temporary fencing prevents accidental contact until the bees complete their life cycle and the adults die off.
Homeowners can encourage ground bees to relocate naturally by altering the nesting site conditions, as these bees prefer sparse vegetation and dry, compacted soil. Improving lawn health by aerating the soil, watering regularly, and adding mulch or ground cover to bare patches makes the area unsuitable for future nesting. These insects play a significant role in local ecosystems, making their conservation a preferable strategy over eradication.