When most people think bees, they think of aboveground hives or perhaps swarms of bees hanging in trees. However, there are several bee species commonly referred to as ground bees, which make their home in the ground.
Like their aboveground counterparts, ground bees gather pollen and nectar. However, they are more solitary and prefer a semi-social environment. Instead of building one shared hive, ground bees burrow in the ground, or appropriate the abandoned holes of rodents and other small mammals. While they often burrow near each other, only one female bee digs each burrow.
Multiple bee species [links to: www.terminix.com/pest-control/bees/types/] are referred to as ground bees, including alkali bees, bumble bees, leafcutter bees, mining or digger bees and sweat bees.
Most species of ground bee are similar in size. They are typically one-half of an inch long or smaller, though some may be up to three-fourths of an inch long. They can be black and yellow, blue, purple, red or green and are often metallic-looking.
They all belong to the same order, Hymenoptera, but are in different families.
People typically notice the males buzzing in large groups during mating season in the spring, or by seeing large numbers of small holes grouped near each other in patches of open ground.
Mating season is March to May, with most species emerging from their underground burrows in March and early April. Because they are solitary bees, there is no queen bee. All female ground bees are fertile. The female bees also serve as worker bees, building the burrows and collecting food for the larvae. Larvae will develop into adult bees while underground, waiting until the next year’s mating season to dig their way out.
During mating season, each female will dig a burrow. These burrows are at least 6 inches deep into the earth, and may have vertical, horizontal or slanted tunnels depending on the species. Most types of ground bee then fill these burrows by laying an egg, pushing in a ball of pollen mixed with nectar and sealing the hole. The young bee will eat the pollen until it is time to exit the burrow the following year.
Most species of ground-dwelling bee are considered semi-social because they build burrows near each other. The clusters of small holes may be unsightly, but these underground colonies aerate the soil and are not harmful to plants or lawns.
Many ground bees are polylectic, meaning they will collect pollen and nectar from multiple plant species. Because of this, farmers often raise them for their help with crop growth.
Alkali bees, Nomia melanderi
This species of bee belongs to the family Halactidae, and is also a type of sweat bee. They nest in the ground, but have a preference for salty soils. They are typically found in the western and southwestern United States. This type of ground bee is also found in salt flats.
They are slightly smaller than honey bees, and are similar in appearance. However, alkali bees have iridescent yellow stripes on a black abdomen. The stripes are made from enameled scales.
Each female bee digs a network of tunnels for her burrow. It is possible for thousands of females to build burrows near each other if a large enough patch of salty earth is available for them to use.
Due to their proclivity for salty soil, these bees are often found in areas that other bees cannot pollinate. Alkali bees are of particular importance to plants in the pea family. These plants are more difficult to pollinate, as the male and female parts of the flower are not exposed initially. Alkali bees land on the flower, bouncing the lower petal or keel to expose the antlers and stamen for pollination. These bees hold particular importance for crops such as alfalfa, a member of the pea family that requires pollination this way. Alfalfa farmers in many states have learned how to attract these bees rather than drive them away because alkali bees can pollinate more than 1,000 flowers per day.
Bumble bees, Bombus pennysylvanicus
American bumble bees are members of the Apidae family. They are black and yellow, and their abdomens are covered in fuzzy hairs that allow them to collect pollen.
They are social bees, unlike other ground-dwelling bees, and they build underground hives. Not all species of bumble bee build their hives underground, though. Of those that do, the bees may burrow into the soil, or just repurpose the abandoned hole of a small rodent or other animal. It is common to find colonies under sheds or in compost piles, in addition to rotting wood.
The hives have a queen bee, helped by drones (male bees) and worker bees. A large bumble bee hive has an average of 400 bees.
Unlike other ground bees that do not make honey, bumble bees make honey with the pollen.
Leafcutter bees, Megachile spp
Leafcutting bees belong to the family Megachilidae. They make their nests in soft or rotting wood or sometimes in plants that have thick, pithy stems, such as roses. They are darker in color than honey bees, but still have light stripes on their abdomen.
They collect pollen, and also cut off semicircular pieces of leaf to line the cells in their nest. After choosing a nest site, a female leafcutter bee will bite off pieces of leaf to use in her burrow. Plants commonly chosen by leafcutter bees for use in burrows include roses, creepers, ash and lilac. Similar to the alkali bee, leafcutter bee colonies are often cultivated by alfalfa farmers for use in crop production.
Mining/Digger bees, Centris pallida
This type of ground bee belongs to the family Andrenidae, and may also be called chimney bees in some parts of the United States. They burrow into soft soil to make their homes, and are sometimes found in desert climates.
Digger bees are quite small, and often have velvety patches on their faces. They can be furry, and are sometimes brightly striped or metallic-green.
As with other ground bees, females seal each egg into a cavity with plenty of pollen. The larvae develop into adults over the summer, but will remain buried until the following spring.
Sweat bees, Lasioglossum spp
Sweat bees belong to the Halictidae family, and are one of the most diverse groups of bee types. About half of the sweat bee species are metallic or dull black in color, while the other half are shades of metallic-blue, green and purple. Unlike other ground bee species, sweat bees may be social, semi-social, solitary or communal.
Sweat bee females carry pollen on their back legs, as opposed to other bee species which typically collect pollen on their abdomens.
After mating season, females dig burrows and fill them with nectar, pollen and eggs. For some species the larvae hatch and emerge quickly, while other species will overwinter in the burrow.
Ground bees are useful pollinators and should not be controlled unless absolutely necessary. Pesticides should be used as a last resort. There are several easy ways to prevent these types of bees from choosing to nest in your yard:
Limit open groundGround bees need open space to dig their burrows. Planting thicker grasses and making sure there are no large, open patches of earth will limit your yard’s attractiveness.
Change the watering systemIf ground bees are already in your yard, water more often. These bees need drier earth to build stable burrows. If you saturate the ground, the bees are likely to leave in search of a better habitat by the next mating season.
Insecticide dustIf you must kill them, use an insecticide dust applied sparingly to the tops of the open burrow holes. Because they are beneficial pollinators, follow all directions and avoid spreading the poison in a wider area than necessary. Also check that the insecticide used is approved for bees.
If you are unsure which species of bee has taken up residence in your yard or the best method to treat the problem, call Terminix® and a Service Technician will help you find a solution.