Many bees live in the ground, a fact often surprising to those accustomed to honeybee hives. These prevalent and diverse insects play a significant role in ecosystems worldwide. Unlike their social counterparts, most ground-nesting bees are solitary, with each female constructing and provisioning her own nest. Understanding these creatures helps appreciate their ecological contributions and docile nature.
Characteristics of Ground-Nesting Bees
Ground-nesting bees are primarily solitary, with each female independently building and provisioning her nest. These bees construct intricate underground galleries composed of a main vertical tunnel and smaller side tunnels, each ending in a brood cell. Females use their mandibles and legs to dig chambers where they lay eggs.
Ground-nesting bees typically select nesting sites in dry, hard-packed soil or bare patches of ground that receive ample sunlight and have good drainage. While some species prefer sandy soils, others utilize loamy or clay-like substrates. The underground environment provides stable temperatures and protection from predators, allowing larvae to mature securely.
Common Types of Ground-Nesting Bees
Several common types of ground-nesting bees exist, each with unique characteristics and nesting behaviors. Mining bees, belonging to the genus Andrena, are often among the first to emerge in spring. They vary in appearance, ranging from the size of a honeybee down to much smaller species, often featuring furry bodies that can be dark, striped, or even metallic green. Female mining bees excavate individual burrows, typically marked by volcano-shaped mounds of soil at the entrance, and while solitary, many may nest closely together in suitable areas.
Sweat bees, primarily from the family Halictidae, are another widespread group, known for their attraction to human perspiration due to its salt content. These bees display a wide range of colors, from iridescent metallic greens and blues to dull blacks, and vary in size from 3 to 10 millimeters. While many sweat bee species are solitary, some exhibit communal, semi-social, or even primitively eusocial behaviors, with nests often found in the ground or occasionally in rotting wood.
Digger bees, including species like Anthophora, are generally robust and hairy, sometimes mistaken for bumble bees, though they lack the specialized pollen baskets of bumble bees. Their tunnels and brood chambers can extend from a few inches to several feet deep. They create small, round holes in loose, sandy soil, with some species forming distinctive chimney-like turrets at their nest entrances.
Cellophane bees, or plasterer bees (Colletes species), are named for their unique nesting habit of lining their brood cells with a waterproof, cellophane-like polymer. These bees often resemble honeybees, with yellowish fuzz and black and yellow stripes, though they are typically smaller. Females excavate burrows, often in sandy soils, and while solitary, they frequently form large aggregations of thousands of individual nests, each containing a single brood cell provisioned with a liquid mixture of nectar and pollen.
Identifying Ground Nests
Recognizing ground-nesting bee nests involves looking for subtle signs on the soil surface. Nest entrances commonly appear as small, circular holes (around 1/4 inch in diameter), often surrounded by a small mound of excavated soil, resembling a miniature volcano or anthill. Cellophane bees, for instance, create pencil-thin holes with small tumuli of sand. Digger bees might construct a distinctive chimney-like turret around their entrance.
Differentiating these bee nests from those of other ground-dwelling insects, such as ants or wasps, is important. Ground-nesting bees, being solitary, typically show only one bee entering or exiting a single hole, unlike social wasps like yellowjackets, where numerous individuals will use a common entrance and exit. The soil grains around a ground bee nest may also be less uniform than those of an ant hill.
Coexisting with Ground-Nesting Bees
Ground-nesting bees are remarkably non-aggressive and pose little threat to humans, rarely stinging unless physically handled or directly provoked. Only the female bees possess a stinger, and unlike social bees that defend a hive, solitary ground bees do not defend their individual nests collectively. Male ground bees, often seen flying actively near nesting sites, do not have stingers and are therefore harmless.
These bees are significant pollinators, often more efficient than honeybees for certain native plants and crops. Their activity supports healthy ecosystems and contributes to biodiversity, ensuring plant reproduction. Their presence in yards is usually temporary, with most species being active for only a few weeks in spring or early summer.
Observing these bees from a distance and avoiding disturbance of their nesting sites are simple ways to coexist. Eradication efforts are generally unnecessary. If their presence becomes a concern, watering the area can encourage them to move, as they prefer dry soil for nesting. Promoting their presence by providing undisturbed, well-drained soil and planting flowering plants supports these beneficial insects and enhances garden health.