Many bee species, often unnoticed, create their homes beneath the ground. While honey bees are well-known for their elaborate hives, about 70% of the world’s approximately 20,000 bee species are ground-nesting. These insects are a common sight in yards and gardens, performing ecological roles. They are diverse pollinators whose subterranean lives contribute to healthy ecosystems.
Identifying Ground-Nesting Bees
Recognizing ground-nesting bees involves observing their appearance and nesting preferences.
Mining Bees
Mining bees (genus Andrena) are common examples, typically 7 to 18 millimeters long. They are often hairy, with bodies that can be black or display metallic blue or green hues. Female mining bees have a velvety patch of hair near their eyes and specialized pollen-carrying hairs, called scopa, on their hind legs and sides of the thorax. They prefer to excavate nests in bare patches of soil, often in sandy areas or at the base of shrubs.
Sweat Bees
Sweat bees (family Halictidae) are another widespread group of ground nesters, usually 3 to 10 millimeters. Their coloration varies widely, from black and brown to metallic greens, blues, or coppers; some species may have striped abdomens. Many are attracted to human perspiration, which provides them with moisture and salts. Most sweat bees construct their nests in the ground, though a few species might use decaying wood.
Bumblebees
Some bumblebee species (genus Bombus) also nest underground. These bees are easily recognized by their robust, fuzzy bodies, often with yellow and black stripes. Unlike many other ground-nesting bees, bumblebees are social and frequently establish colonies in pre-existing cavities, such as abandoned rodent burrows or dense grass.
Distinguishing ground-nesting bees from wasps, like yellowjackets, is important. Bees are generally hairier and more robust, while wasps are typically more slender with smoother bodies and a noticeable “wasp waist.” Wasps also show high traffic at their nest entrances, unlike solitary bees.
Underground Nesting Habits
Ground-nesting bees exhibit various strategies for building their subterranean homes.
Solitary Bees
The majority are solitary species, meaning each female independently constructs and provisions her own nest. A female solitary bee typically digs a main burrow, which can extend several inches into the ground, often reaching depths of six inches or more. Branching off the main tunnel are multiple side tunnels, each ending in a small chamber called a brood cell.
The female collects pollen and nectar, forming a pollen ball within each cell, upon which she lays a single egg. The walls of these brood cells are often lined with a waxy, cellophane-like material that helps protect the developing larva from moisture and fungi. The larva feeds on the provisioned pollen and nectar, develops through pupation, and typically emerges as an adult the following spring.
Social and Communal Bees
While most ground-nesting bees are solitary, some species, like certain sweat bees, can exhibit semi-social or communal behaviors. They occasionally share an entrance tunnel but maintain individual brood cells. Bumblebees, being social insects, operate differently.
Their queens establish nests in existing underground cavities, often abandoned rodent nests or other sheltered spaces. These social nests, though smaller than honey bee hives, can grow to house between 50 and 400 individuals, including the queen, workers, and new queens and males.
Ecological Importance
Ground-nesting bees play an important role in maintaining ecosystem health. Their primary function is pollination, contributing to the reproduction of a wide array of plants. These include native wildflowers, important for biodiversity, as well as many garden vegetables and fruit trees that contribute to human food systems. Over 80 species of wild bees, many of which are ground-nesters, visit apple blossoms, and they are key pollinators for crops such as tomatoes and melons.
Ground bees are often efficient pollinators, sometimes more effective than honey bees for certain plants. Their foraging behaviors, such as buzz pollination (sonication) employed by some sweat bees and mining bees, can release pollen from flowers that other pollinators might miss. This specialized technique involves the bee vibrating its flight muscles while grasping the flower, causing pollen to dislodge. Their consistent activity across diverse plant species supports healthy plant communities and ensures the propagation of both wild and cultivated flora.
Living Alongside Ground Bees
Coexisting with ground-nesting bees is straightforward due to their non-aggressive nature. Most solitary ground bees are docile and rarely sting unless directly handled or stepped on. Male bees, often seen flying near nest entrances, are incapable of stinging. This makes them safe to have in residential areas, even with children and pets present.
Observing these bees from a respectful distance allows for appreciation without disturbance. To support ground-nesting bees, consider leaving patches of bare, well-drained soil undisturbed in sunny areas of your yard. Avoiding pesticides is important, as these chemicals can harm bees and their developing young.
Planting a variety of native plants provides pollen and nectar resources throughout the season. Allowing autumn leaves to remain on the ground until spring can offer cover for underground nests. If their presence becomes a concern in a specific area, heavy watering can sometimes encourage them to relocate their nesting sites.