Many bee species build nests in the ground, a contrast to the familiar image of bees in above-ground hives. Approximately 70% of the world’s 20,000 bee species are ground-nesters, leading largely solitary lives. These bees construct their own burrows, often in areas with exposed soil, thin grass, or good drainage.
Common Ground-Nesting Bee Species
Several types of bees commonly nest in the ground, each with distinct features. Mining bees (genus Andrena) are among the most abundant, with over 1,500 species worldwide. These bees vary in size from 5 to 17 millimeters, and are often black with dull metallic green or blue coloring, characterized by grooves running down the inside of their eyes. They collect pollen on their hind legs and are active from early spring, making them important early pollinators.
Sweat bees (family Halictidae) are a diverse group with over 2,000 species worldwide. They are generally smaller than honeybees, ranging from 3 to 10 millimeters, and exhibit a wide array of colors from dark brown or black to striking metallic greens, blues, or bronze. Some species are attracted to human perspiration for its salt content, which gives them their common name. Many sweat bees also have pale bands on their abdomens.
Cellophane bees (genus Colletes), also known as plasterer or polyester bees, are medium-sized with fuzzy bodies and heart-shaped faces. They are similar in appearance to honeybees but are distinguished by more prominent antennae and dark abdomens with thin, pale yellow bands. These bees uniquely line their brood cells with a cellophane-like, waterproof secretion, which protects their developing young from moisture.
Digger bees are robust, fast-flying bees with velvety fur. They range in size from that of a honeybee to a bumblebee, with some species displaying metallic blue or green hues. Males of some digger bee species, like Anthophora abrupta, have a distinctive “mustache” of hairs on their face. They are known for their complex nesting behaviors and are found globally.
Characteristics of Ground Nests and Bee Behavior
Ground-nesting bees create burrows. The entrance often appears as a small, round hole, typically about 1/4 inch in diameter, sometimes surrounded by a small mound or “volcano” of excavated soil. These bees prefer well-drained, sandy or loamy soils, and areas with sparse vegetation or bare ground.
Most ground-nesting bees are solitary, meaning each female independently constructs and provisions her own nest, laying eggs and supplying them with pollen and nectar for her offspring. Unlike social bees such as honeybees, solitary bees do not have a queen or a worker caste, and there is no cooperative care for the young within a single nest. However, many solitary species will nest in close proximity to one another, forming large aggregations that can contain hundreds or thousands of individual nests. Despite this close clustering, each nest remains independent, and the bees do not share resources or defend a communal territory.
Ground-nesting bees are generally non-aggressive. They are primarily focused on their nesting and foraging activities. Female ground bees typically only sting if they are directly threatened, such as being stepped on or handled. Male ground bees, which are often observed flying around the nesting sites, do not possess stingers.
Their Ecological Role
Ground-nesting bees play a significant role as pollinators within various ecosystems. As they forage for nectar and pollen to provision their brood cells, they facilitate pollen transfer between plants, essential for plant reproduction. This pollination service supports native wildflowers, garden plants, and many agricultural crops.
These bees are efficient pollinators, visiting hundreds of flowers daily. Some species are generalists, collecting pollen from a wide variety of plants, while others are specialized, focusing on specific plant families. Their activity contributes to biodiversity and helps maintain healthy plant communities. Beyond pollination, their nesting activities also contribute to soil aeration and turnover, enhancing soil health.
Coexisting with Ground Bees
When encountering ground-nesting bees, it is best to leave them undisturbed. Their presence is usually temporary, as most species are active for only a few weeks in spring or summer. Identifying their nests by the small holes with surrounding soil mounds helps avoid accidental disturbance.
Because ground-nesting bees are not typically aggressive and rarely sting unless directly provoked, they pose minimal risk in a garden or yard. To avoid stings, avoid walking barefoot in nesting areas and refrain from disturbing their burrows. If a bee is trapped against skin or clothing, a sting may occur.
In cases of severe allergies, or if a very large aggregation is in a high-traffic area, professional consultation might be considered. Pesticides can harm these beneficial pollinators and are not recommended for managing ground bees due to their ecological importance and docile nature. Simple measures like increasing ground cover or watering preferred areas to keep the soil moist can encourage them to relocate without harm.