Approximately 70% of the world’s 20,000 bee species are ground-nesting, creating their homes beneath the earth’s surface. Unlike honeybees, many ground-nesting species are solitary, constructing intricate underground tunnels and chambers for raising their young.
Common Ground-Nesting Bee Species
Mining Bees (genus Andrena) are widespread, varying in size from 5 to 17 millimeters and often appearing dark-colored with light or dark hairs. Females typically have prominent pollen-carrying hairs on their hind legs and a line of light hairs along the inner edge of their eyes. They are crucial pollinators for early-blooming fruit trees and wildflowers.
Digger Bees (genera Anthophora and Melissodes) are robust, fast-flying bees, ranging from 4 to 16 millimeters in length. They can be black, brown, or metallic, with some species exhibiting striking patterns. Males often have exceptionally long antennae, giving some species the name “longhorned bees.” Digger bees are known for their industrious digging abilities and are effective pollinators across a wide variety of flowers.
Sweat Bees (family Halictidae) are a diverse group, ranging from small to medium-sized (3 to 10 millimeters). While many are black or brown, some species display vibrant metallic green, blue, or even purple coloration. Their name comes from their occasional attraction to human perspiration, which provides them with salts. Some sweat bee species are solitary, while others can be communal or semi-social.
Some Bumblebees (genus Bombus) also nest underground, often utilizing abandoned rodent burrows or other pre-existing cavities. Unlike most other ground-nesting bees, bumblebees are social, forming colonies with a queen and workers. They are relatively large, typically ranging from ¾ to 1 ½ inches, and are covered with dense, spiky hair, often displaying stripes of orange, white, or yellow.
Characteristics of Their Nests
Ground-nesting bees construct their nests in various soil conditions, often preferring areas with bare or sparsely vegetated ground that receive good sun exposure and are well-drained. The entrance to a ground bee nest typically appears as a small, circular hole, about ¼ to ½ inch wide, often surrounded by a small mound of excavated soil resembling a miniature volcano or anthill. These mounds are composed of the soil the bee removed during tunnel construction.
Beneath the surface, nests consist of a main tunnel that branches off into individual brood cells. Female bees meticulously prepare these cells, provisioning them with a mixture of pollen and nectar, often called “bee-bread,” to feed their offspring. A single egg is laid on this food supply, and the cell is then sealed. Some species, like cellophane bees (Colletes spp.), line their brood cells with a polyester-like secretion, creating a waterproof barrier that protects the developing young. The depth of these tunnels can vary significantly by species, from a few inches to several feet deep, with some extending nearly 10 feet underground.
Behavioral Traits and Ecological Importance
Most ground-nesting bees are solitary, with each female independently constructing and provisioning her own nest. While they do not form cohesive colonies like honeybees, multiple solitary nests may be found in close proximity, sometimes creating large aggregations. However, these females do not typically interact or help each other.
Ground-nesting bees are generally non-aggressive and rarely sting unless directly threatened or handled. Female ground bees possess a stinger but are reluctant to use it. Male ground bees, often seen flying around nesting areas in search of mates, do not have stingers and are harmless.
These bees are vital pollinators, playing a significant role in the reproduction of various plants, including agricultural crops and wildflowers. They collect nectar and pollen from a wide range of flowering plants. Their activity also benefits soil quality, as their burrowing habits help aerate the soil and improve water and nutrient penetration. Many ground-nesting species are among the earliest pollinators to emerge in spring, making them particularly important for early-blooming plants.
Differentiating Ground-Nesting Bees from Other Insects
Distinguishing ground-nesting bees from other ground-dwelling insects, especially more aggressive wasps, is important for safety and conservation. Ground-nesting bees are often mistaken for yellow jackets or cicada killers. A key difference lies in their social behavior and nest activity. Ground-nesting bees typically show only one bee entering or exiting a small hole. In contrast, yellow jacket nests exhibit constant, high-traffic activity with many individuals entering and leaving a single, often wider, entrance.
Appearance also provides clues. Many ground-nesting bees have fuzzy bodies, varying in color from black and brown to metallic green or blue. Yellow jackets are typically smoother-bodied with distinct, brighter yellow and black stripes. Cicada killers are much larger wasps with black bodies marked with yellow bands. While they also dig in the ground, their size and the presence of paralyzed cicadas near their burrows are distinguishing features.