Many types of bees create their homes beneath the ground, a fascinating behavior often unseen by the casual observer. While honey bees are known for communal hives, a significant majority of bee species (70% to 90%) are solitary and nest underground. These ground-dwelling bees are common in various landscapes, yet their subterranean lives often remain a mystery. Understanding them reveals a diverse and important group of pollinators vital to ecosystems.
Common Ground-Nesting Bees
Mining bees (Andrena) are frequently encountered ground-nesting bees. These solitary bees are typically black with varying hair shades, ranging from 5 to 17 millimeters. They are among the first bees to emerge in early spring. Females excavate tunnels in the soil, often leaving small, volcano-shaped dirt mounds at the entrance. Mining bees are important pollinators, especially for early-blooming fruit trees like apples, cherries, and plums.
Sweat bees (Halictidae) are a widespread group of ground nesters. Their appearance varies considerably; many are small, slender, and brown or black, while others exhibit striking metallic green, blue, or purple coloration. Most species nest in the ground, though some use rotting wood. While many are solitary, some sweat bees display semi-social behaviors. They are also known for their ability to “buzz-pollinate” certain flowers.
Digger bees (Anthophoridae) are robust and furry, often larger than honey bees, and can be mistaken for bumblebees. They typically construct nests in various soil types, including clay banks or flat ground. Digger bees are recognized for their rapid, hovering flight patterns and their efficiency in pollinating plants, often through buzz pollination.
Bumblebees (Bombus species), though often perceived as above-ground dwellers, also nest in the ground. These social insects establish colonies in existing subterranean cavities, such as abandoned rodent burrows. They are identifiable by their stout, hairy bodies and distinct black and yellow or orange bands. Unlike most other ground-nesting bees, bumblebees live in colonies with a queen and workers and will defend their nests if threatened.
Why Bees Nest in the Ground
Ground-nesting offers bees several advantages for raising their young. The subterranean environment protects them from predators. The soil also acts as a natural insulator, regulating temperature and maintaining stable conditions for developing larvae, shielding them from extreme heat or cold. Additionally, soil stability provides a secure structure for their intricate tunnel systems.
Female ground-nesting bees excavate burrows using their mandibles and by pushing soil with their abdomens. Nests can vary in depth from a few inches to 10 feet, depending on the species. While most are solitary, with each female building and provisioning her own nest, many individuals may nest in close proximity, forming large aggregations in favorable areas.
Bees often select specific soil characteristics for their nests. Many species prefer well-drained, sandy soils, while others opt for hard-packed clay. Sunny, bare ground with sparse vegetation is particularly attractive. South-facing slopes are also preferred, as the sun warms the soil, making it easier to dig and providing a suitable environment for offspring.
Ground Bees and Humans
Ground-nesting bees are generally not aggressive and pose little threat to humans. Most solitary species only sting if directly threatened, such as when stepped on or trapped. Male ground bees, often seen hovering near nest entrances, lack stingers entirely and are harmless. While social bumblebees may defend their nests more readily, they are still unlikely to sting unless provoked.
These bees play a significant ecological role as pollinators. They efficiently pollinate a wide range of plants, including important agricultural crops like apples, blueberries, and cherries. Some ground-nesting bees perform “buzz pollination,” a specialized technique releasing pollen from flowers like tomatoes, which honey bees cannot. Their tunneling activities also naturally aerate the soil.
Coexisting peacefully with ground bees is straightforward and beneficial. If nests appear in areas of concern, simple methods can encourage relocation without harm. Since these bees prefer dry soil, consistently watering an affected area can prompt them to move. Maintaining a dense, healthy lawn also reduces bare spots, making areas less attractive for nesting. Recognizing their importance as pollinators, leaving undisturbed, sunny patches of bare soil in less trafficked yard areas provides suitable nesting habitats.