The Halictidae family, commonly known as sweat bees, is a large family of nearly 4,500 species found across every continent except Antarctica. These native pollinators are generally small, ranging from 3 to 10 millimeters in length, and often display striking metallic colors like brilliant green, blue, or bronze. Their common name originates from their attraction to human perspiration, which provides them with the salts and moisture needed to supplement their diet of nectar and pollen. Although drawn to human skin, these bees are not aggressive, and their nesting habits are centered beneath the soil surface.
Preferred Environments for Ground Nesting
The majority of sweat bee species are ground nesters, making the selection of a subterranean location the first step in their reproductive cycle. They seek ground that is stable yet easy to excavate, often preferring bare soil, sparse lawns, or areas with minimal vegetation cover. This preference helps ensure the chosen spot receives ample sunlight, which warms the ground and aids in brood development. Many species favor well-drained materials like sandy loam or firm clay.
Hard-packed ground, such as walking paths or the banks of ponds and streams, is frequently chosen because it offers stability and a reduced risk of tunnel collapse. The depth of these nests can vary significantly, with some species creating shallow structures only a few centimeters deep, while others excavate elaborate tunnels that extend over a meter below the surface. A small minority of sweat bees will opt for alternative nesting sites, such as rotting wood or hollowed-out plant stems.
Nest Architecture and Social Organization
Once the location is established, the female bee begins constructing her nest, which starts with a single, main vertical shaft descending into the ground. This main tunnel then branches out into lateral tunnels, each leading to individual brood cells. The female provisions each cell with a mixture of pollen and nectar, known as a pollen ball, upon which she lays a single egg.
The brood cells are meticulously constructed and often lined with a thin, waxy substance secreted by the bee. This lining helps to waterproof the chamber and protect the developing larva. The social organization of sweat bees is incredibly diverse, displaying a full spectrum of behavior that influences the final nest structure.
Solitary species feature a single female who performs all the tasks of digging, provisioning, and egg-laying alone. Other species are communal or semi-social, where several females may share the main entrance tunnel but each maintains and provisions her own lateral tunnels and brood cells. In the most complex, primitively eusocial species, a division of labor exists. A founding female (queen) produces a generation of smaller, non-reproductive daughters (workers) who help with nest maintenance and foraging. This flexible social structure means that a nest may house anywhere from a single bee to a small colony of a dozen or more individuals.
Identifying Sweat Bees and Their Burrow Entrances
Identifying a sweat bee nest is relatively straightforward, as the entrance often leaves a distinctive mark on the soil surface. The burrow entrance is typically a single, small, round hole, sometimes surrounded by a tiny, cone-shaped mound of loose, excavated soil. These soil mounds are generally smaller and less prominent than the larger craters created by ant colonies or the mud tubes of some wasps, which helps to distinguish the nest site.
A key behavioral indicator is the activity around the entrance, which may be sealed with soil when the bee is absent or at night to deter predators. The bees themselves are small and can appear black or brown, but the most recognizable species flash a brilliant metallic sheen of green or blue. Sweat bees are not aggressive and will only sting if they are accidentally trapped or pressed against the skin.