Many bee species, contrary to the common image of bees in large hives, actually live and nest in the ground. These ground-nesting bees represent approximately 70% of the world’s 20,000 bee species. They lead solitary lives, with each female constructing and caring for her own nest within the soil. These bees are commonly found in gardens and yards, where their presence might go unnoticed.
Why Bees Nest in the Ground
Ground-nesting is a widespread and advantageous strategy for many bee species. Bees seek specific soil conditions for their underground homes, often preferring well-drained, sandy, or loamy soils, and bare patches. Some species may also favor clay-rich soils or areas with minimal vegetation. The soil provides a stable environment, offering protection from predators and insulation against temperature extremes for their developing offspring. Female bees meticulously excavate tunnels and cells, sometimes lining them with specialized secretions to create a waterproof barrier.
Key Ground-Nesting Bee Species
Several ground-nesting bee species exist, each with unique characteristics.
Mining Bees
Mining bees (Andrena genus) are common ground-nesting bees, often seen in early spring. They are medium-sized with reddish-golden or black and ash-grey hairs; females have prominent pollen-carrying hairs on their hind legs. Mining bees excavate tunnels in bare or sparsely vegetated soil, creating small, volcano-shaped mounds of dirt at their nest entrances. While solitary, many individuals may nest in close proximity, appearing as a larger colony.
Digger Bees
Digger bees (Anthophora and Centris genera) are another group of ground nesters. These bees are medium to large-sized with hairy bodies, sometimes appearing metallic blue or green. Known for strong digging abilities, they often prefer to nest in banks or compacted soil. Females construct complex tunnels and cells underground, provisioning them with nectar and pollen for their larvae.
Sweat Bees
Sweat bees (Halictidae family) are recognizable by their metallic sheen, which can be green, blue, or purple. Their size varies from small to medium, typically 3 to 15 millimeters. While many are solitary, some species exhibit communal nesting behaviors, usually in the ground. They are attracted to human perspiration for its salt content, giving them their common name.
Bumblebees
Some bumblebee species (Bombus spp.) also nest underground, but their habits differ. Instead of digging their own burrows, they commonly utilize existing cavities like abandoned rodent burrows or dense grass clumps. Bumblebees are robust and fuzzy, often with distinct black and yellow stripes. Their nests are social colonies, contrasting with the solitary nature of most other ground-nesting bees.
Spotting Ground Bee Nests
Ground bee nests can be identified by specific visual cues in your yard or garden. One common sign is small, volcano-shaped mounds of soil, typically a few inches across, with a distinct hole in the center. These mounds are created as the female bee excavates soil from her burrow. The entrance holes are small, often resembling a pencil’s diameter. You might notice bees actively entering or exiting these holes, particularly during warmer parts of the day.
Differentiating ground bee nests from those of other insects like ants or wasps is important. Ant hills are smaller and consist of finer soil particles compared to the larger, more defined mounds of ground bees. Ground-nesting yellow jackets, a type of wasp, typically have a single, larger entrance to their communal nest, with many insects constantly flying in and out. In contrast, ground bees, being mostly solitary, usually have only one bee entering or leaving a particular hole. Wasps tend to be more aggressive and may swarm if their nest is disturbed, unlike docile ground bees.
Living Alongside Ground Bees
Ground-nesting bees are not aggressive and pose little threat to people or pets. Most are solitary; females sting only if directly provoked or accidentally stepped on. Male ground bees, often observed flying around nesting areas in search of mates, do not possess stingers.
These bees play a significant role as pollinators for many plants, including various crops, wildflowers, and fruit trees. Their activity is temporary, lasting a few weeks during emergence in spring or summer.
To coexist with ground bees, leave their nests undisturbed. Avoiding walking barefoot in areas with visible nests prevents accidental encounters.
Using pesticides is not recommended, as it harms these beneficial pollinators. More bees may return the following season if soil conditions remain favorable. Protecting areas with bare soil can provide suitable nesting habitats for these important insects.