Many people associate bees with honeycombs hanging from trees or hives, yet a significant number of bee species build their nests underground. These ground-nesting bees are a common and natural part of many ecosystems, playing a crucial role in the environment. Their presence often goes unnoticed or is sometimes confused with other ground-dwelling insects. Understanding these subterranean dwellers reveals a diverse world of pollinators vital to healthy plant life.
Common Ground-Nesting Bee Species
A large portion of the world’s bee species, approximately 70%, are ground-nesting. Several common types exist, each with distinct characteristics and nesting habits. Miner bees, belonging to the genus Andrena, are among the earliest native pollinators to emerge in spring. They are typically small to medium-sized, ranging from 7 to 18 mm, often black or dull metallic blue or green, and quite hairy. These solitary bees excavate tunnels in bare or sparsely vegetated soil, often preferring sandy conditions. While each female builds her own nest, many miner bees will create nests in close proximity, forming large aggregations that can number in the thousands.
Sweat bees, part of the Halictidae family, are a widespread group, encompassing nearly 4,500 species. They vary greatly in appearance, from dark-colored to striking metallic green, blue, or purple hues. Typically tiny to medium-sized (3-10 mm), most nest in various soil types, displaying behaviors from solitary to primitively social.
Bumblebees (Bombus spp.) are frequent ground nesters, and unlike many solitary ground bees, are social insects. After hibernation, a queen bumblebee searches for a suitable underground cavity, often an abandoned rodent burrow, to establish her colony. These nests are much smaller than honeybee hives, typically housing a few hundred bees, with wax cells for brood, pollen, and nectar. Some species may also nest on the surface, in dense grass or mossy vegetation.
Distinguishing Ground Bee Nests
Identifying a ground bee nest involves observing specific visual cues that differ from other ground-dwelling insects like ants or wasps. Ground bee nests typically appear as small holes in the soil, often surrounded by a small pile of excavated dirt, or conical mounds. These entrance holes are usually small (1/4 to 1/2 inch in diameter), allowing only a single bee to enter or exit. Soil particles around a ground bee nest entrance may vary in size, unlike the uniform grains often seen around ant nests.
In contrast, yellow jackets, aggressive wasps often mistaken for ground bees, typically have larger nest entrances (over an inch wide), with many insects constantly flying in and out. Their nests might look like a busy airport with continuous traffic, while a ground bee nest usually sees only one bee entering or leaving at a time. While some ground bees, like digger bees, might form turrets at their nest entrances, the entrance’s overall appearance and activity level remain key distinguishing factors. Ground bee nests are generally found in areas with bare ground, sparse vegetation, and well-drained, often sandy soil.
Understanding Ground Bee Behavior
Most ground-nesting bees are not aggressive and sting only if directly threatened or provoked (e.g., stepped on or handled). Males lack stingers entirely and are often seen flying actively around nest sites seeking mates. Even female ground bees, while possessing a stinger, are generally docile and do not defend nesting areas like social honeybees or wasps. Their primary focus is foraging for pollen and nectar and provisioning individual nests.
Ground-nesting bees are important pollinators for wildflowers and various crop plants, including blueberries, apples, and cherries. Their activity significantly contributes to the pollination of flowering plants, supporting ecosystems and food production. These bees also indirectly benefit soil health, as their burrowing activities aerate the ground, improving water and nutrient penetration. If nests are found, observe them from a distance and avoid disturbance, as these beneficial bees are often temporary residents. If removal is deemed necessary, non-toxic methods like watering the area to encourage relocation are preferred over pesticides, as ground bees prefer dry soil.