Ground-nesting bees are a diverse group of insects, distinct from the more commonly known social bees like honeybees. They construct individual nests in the ground rather than forming large colonies with a queen and worker bees. Though often unnoticed, ground-nesting bees are a common presence in many environments, contributing to ecosystem health. Approximately 70% of the world’s 20,000 bee species lay their eggs in underground nests.
Common Ground-Nesting Bee Species
Mining Bees (Andrena) are widespread ground-nesting bees. They are medium-sized, fuzzy, often black with light or dark hairs, and can be mistaken for honeybees. These solitary bees excavate tunnels and chambers in bare or sparsely vegetated soil, often preferring sandy areas. While individual females maintain their own nests, many may nest in close proximity, creating large aggregations that can appear like a colony.
Cellophane Bees (Colletes spp.), also known as plasterer bees, line their underground nests with a cellophane-like, waterproof secretion. They are solitary, with females constructing individual nests, though they often aggregate in suitable sites. Nests are typically found in loose, sandy, well-drained soil.
Digger Bees (Anthophora spp. or Centris spp.) are fuzzy and vary in size, sometimes resembling bumblebees, but they lack pollen baskets. They create tunnels and chambers in the soil, often in clay. While each female constructs her own nest, digger bees frequently form large nesting aggregations.
Sweat Bees, primarily from the family Halictidae, are a diverse group that includes species with metallic green, blue, or dull metallic bodies, and they range in size from 3-10 millimeters. Most sweat bees nest in the ground, preferring stable, easily excavated soil like clay, or even rotting wood. Some species exhibit varying levels of social behavior, from solitary to semi-social, with some even sharing nest entrances.
Identifying Ground Nests
Ground bee nests have small, distinct openings in the soil, about 1/4 inch in diameter. These openings often have a small mound of excavated dirt around them, resembling a miniature volcano or an anthill, though the soil particles are larger. Each opening leads to a single bee’s tunnel, distinguishing them from social insect nests like yellowjacket colonies, which have a single large opening for many insects.
Ground bees prefer areas with exposed, bare soil, thin grass, or sparse vegetation. Sunny, well-drained spots with sandy or loose soil are favored for nesting. The depth of these tunnels varies from a few inches to several feet, depending on the bee species.
Behavior and Interaction
Ground-nesting bees are predominantly solitary. Each female bee constructs and provisions her own nest independently. Unlike social bees, they do not defend a communal hive, making them non-aggressive towards humans and pets. These bees will only sting if directly provoked, handled, or accidentally stepped on.
Male ground bees, which do not possess stingers, may appear more active or aggressive as they patrol nesting areas seeking mates. However, their behavior is harmless. To coexist with ground bees, observe them from a distance and avoid disturbing their nesting sites. Watering the area may encourage them to relocate, as they prefer dry soil.
Their Role in Ecosystems
Ground-nesting bees are important pollinators, with a significant role in natural ecosystems and agriculture. They pollinate a wide variety of native plants, wildflowers, and food crops like blueberries, apples, and cherries. Some species are specialist pollinators, focusing on specific plant types, which makes them efficient for those plants.
Their foraging activities are essential for plant reproduction and maintaining biodiversity. Ground-nesting bees also improve soil aeration through their digging. Protecting these beneficial insects by preserving their nesting habitats supports healthy ecosystems.