Many bee species, unlike the familiar honeybee, do not live in communal hives above ground. Around 70% of the global bee population are solitary insects that build nests beneath the earth’s surface. These ground-nesting bees are common in yards and gardens, often marked by small soil mounds at their nest entrances. Generally docile, they play an important role in local ecosystems.
Common Types of Ground-Nesting Bees
Mining Bees (Andrena species) are solitary and construct tunnels in well-drained soil. They vary from 5-17mm, often displaying dark bodies with pale hair bands across their abdomens and dense thoracic hair. Females possess specialized pollen-collecting hairs (scopae) on their hind legs. Their nests are frequently marked by small, volcano-like piles of excavated soil. Mining bees are active for 6-8 weeks in early spring, and are crucial pollinators for early-blooming plants.
Digger Bees are robust, fast-flying bees with velvety fur that nest in the ground. They range in size from honeybees to bumblebees, with some species displaying stout, furry black and yellow bodies. Known for their digging abilities, they create tunnels several inches to feet deep. Some species construct chimney-like turrets at their nest entrances. While solitary, digger bees often form nesting aggregations, with males actively searching for emerging females around these sites.
Sweat Bees are a diverse group of ground-nesting bees, with over 4,300 species worldwide. They vary in size and coloration, from tiny black bees to metallic green, blue, copper, or reddish-brown hues. Sweat bees can be solitary or social, with some species forming interconnected tunnels underground. They are important pollinators, frequently seen collecting nectar and pollen from a wide array of flowering plants.
Cellophane Bees, also known as Plasterer Bees, are medium to small bees often covered in fine, silky hairs. They are named for lining their underground nest cells with a waterproof, cellophane-like secretion from their salivary glands. This lining protects developing larvae from moisture and fungal pathogens. Cellophane bees typically have heart-shaped faces and pale stripes on their abdomens. While solitary, they often nest in large aggregations, sometimes numbering in the thousands.
Why Bees Choose the Ground for Nesting
Bees select the ground for nesting due to environmental factors that offer protection and support for their offspring. Soil composition is a primary consideration; many ground-nesting bees prefer loose, friable, sandy soils that are easy to excavate. Some species can also nest in well-drained clay soils. Bare ground or sparsely vegetated areas are favored, as dense plant cover can hinder digging and access to nest entrances.
Sun exposure is another important element, as many species prefer warm, sunny locations, especially south-facing slopes. The sun’s warmth helps regulate nest temperature, crucial for egg and larval development. Soil also provides natural insulation, shielding developing young from extreme temperature fluctuations and adverse weather conditions. This subterranean environment offers a stable microclimate, beneficial for the survival and development of bee larvae over several months.
Life Cycle and Behavior of Ground Nesters
The life cycle of a solitary ground-nesting bee begins when a female, after mating, constructs her nest in the soil. She excavates a main tunnel, often with several short side tunnels branching off, forming individual brood cells. The female then lines each cell, sometimes with a waterproof secretion, to protect her offspring.
Following nest construction, the female provisions each cell with a mixture of pollen and nectar, often shaped into a “bee bread” ball. A single egg is laid on this food supply, and the cell is sealed. Larvae hatch and feed on the stored provisions, growing and developing within their secluded cells. They typically overwinter in the pupal stage underground, emerging as adult bees the following spring to mate and continue the cycle. Adult ground-nesting bees are active foragers, collecting pollen and nectar from flowers, and are significant pollinators for various plants, some even specializing in particular plant species.
Coexisting with Ground Bees
Ground-nesting bees are generally non-aggressive and pose little threat to humans, rarely stinging unless provoked or accidentally stepped upon. Unlike social bees that defend a communal hive, solitary ground bees do not have a large colony to protect, making them much less likely to sting. Male ground bees, often seen flying actively around nesting areas in search of mates, lack stingers entirely and are therefore harmless.
These bees are important pollinators for both wild plants and agricultural crops, often emerging early in the season and providing essential pollination services for early-blooming flora. Their presence can benefit lawns by aerating the soil through their digging activities. If nests are in an inconvenient location, such as a high-traffic area, gentle deterrence methods can be employed. Ground bees prefer dry soil, so consistently watering the area before their typical emergence can encourage them to nest elsewhere without harm.