When you picture a bee, a honeybee hive might immediately come to mind. However, approximately 70% of the world’s over 20,000 bee species prefer to make their homes beneath the soil surface. These ground-nesting bees are widespread, found in gardens, parks, and wildlands. Unlike social bees, most lead solitary lives. Their presence indicates a healthy ecosystem and they are typically docile, posing little threat to humans or pets.
Identifying Ground-Nesting Bees
Recognizing ground-nesting bees often involves observing both the insects themselves and the distinct signs of their nests. These bees vary in appearance, with sizes typically ranging from one-half to three-quarters of an inch. Their coloration can be diverse, including shades of black, blue, green, copper, or metallic red, and some may have fuzzy or hairy bodies. They generally have a more compact size and a low, rapid flight pattern compared to larger, more airborne bee varieties.
The most recognizable visual cues of their presence are their nests, which appear as small, distinct holes in the ground. These holes are often about 1/4 to 1/2 inch wide, just large enough for a single bee to enter or exit. Around the entrance, you might observe a small, cone-shaped mound of excavated soil, resembling a miniature volcano. These nests are commonly found in sunny, well-drained areas, often in bare or sparsely vegetated ground, as these conditions are ideal for burrowing and provide warmth for developing young.
While individual nests are managed by a single female, favorable soil conditions can lead to many bees nesting in close proximity, creating what appears to be an aggregation of individual nests rather than a single colony. Common examples include mining bees (Andrena spp.), often among the first to emerge in spring; cellophane bees (Colletes spp.), known for waterproofing their nests; and sweat bees (Halictus spp.), a very common and diverse group.
Behavior and Nesting Habits
Ground-nesting bees exhibit unique behaviors centered around their subterranean homes. They are solitary bees, meaning each female independently constructs her own nest tunnel and provisions it for her offspring, unlike social bees that live in large colonies. Each female uses her mandibles and forelegs to excavate a main tunnel, which can range from a few inches to several feet deep, with some extending nearly ten feet.
Along this main tunnel, the female bee creates multiple side chambers or cells. She provisions each cell with a ball of pollen and nectar, collected from various flowers, before laying a single egg. Some species, like cellophane bees, line their nests with a waterproof, cellophane-like secretion to protect the eggs from moisture and fungi. This process ensures the developing larvae have a food source until they emerge as adults, typically the following year.
These bees are non-aggressive; they are unlikely to sting unless directly provoked or accidentally stepped on, as they do not defend a large honey store or complex colony. Male ground-nesting bees, which lack stingers and are harmless, are often seen patrolling nesting areas in search of mates.
Ecological Importance and Living Alongside Them
Ground-nesting bees contribute to local ecosystems and agriculture. They are efficient pollinators for a wide array of flowering plants, including native species, fruit trees, and various crops like apples, blueberries, tomatoes, and melons. Their foraging activities support overall biodiversity and food production. Beyond pollination, their burrowing habits aerate the ground, improving water and nutrient penetration into the soil and benefiting plant growth.
Coexisting with these beneficial insects involves understanding their temporary presence and docile nature. Their activity is most noticeable in early spring, when adults emerge for mating and nesting, usually lasting a few weeks to a couple of months depending on the species. To live peacefully alongside them, avoid disturbing their nesting sites, especially during active periods. Refrain from using broad-spectrum pesticides in areas where they are active, as these chemicals can be harmful to them and other pollinators.
If nests are in an inconvenient location, such as a high-traffic area, altering the soil conditions can encourage them to relocate. Ground-nesting bees prefer dry, well-drained, and sparsely vegetated soil for nesting, so consistently watering the area or increasing lawn density with healthy turf can deter them from nesting there in subsequent seasons.