What are ground nesting bees?

As its name indicates, ground nesting bees are bees that nest in the ground mostly by digging their nests. Ground nesting bees are found in several families of bees, and being a soil nester/digger is actually one of the most common nesting strategies among solitary bees. Once the female finds a good nesting site, she starts excavating it to create an underground nest, which often has several brood cells, in which the larvae develop. These nests are usually found in spaces where the vegetation is sparse or the soil bare, and can sometimes be built along with other nests of the same species, leading to communal nesting areas. It is because of this preference for relatively open ground, that it is often recommended that at least some uncovered ground is left in our green spaces, which helps provide habitat for their establishment.

How do ground nesters build their nests?

As good miners or soil diggers, ground nesting bees also have specific behavioral and morphological traits that make them good at what they do. Bees that excavate have modified leg structures that allow them to easily move within tunnels, strong mandibles that they use to actually dig the cavity, and modified extremes of the abdomen (the pygidial plate) that function as sorts of trowels and allow them to pack soil on the walls of the cavity they are digging.

Along with having the right tools of the trade, these bees also are selective of the type of soil they use to build their nests. Most ground nesting bees prefer soils that are not too compacted, with at least some sand content, which makes them easier to dig through. This means that it is more likely that we will find these bees in rockier/sandier soils, than in super clay-y ones.

Because digging through the soil with their mandibles (and sometimes their legs) is hard work, bees usually tend to choose the best timing to start their digging. In fact, the hardest part of the soil to dig through for a bee is the surface, which is often the most compacted. For this reason, bees tend to start digging after the soil has become moist (e.g., after rains). Incredibly, some ground digging bees are even able to add, if needed, secretions or even nectar to humidify and loosen the soil! Once the bee has started her excavation, she continues digging deeper and bringing soil out of the construction area, which leads to often sorts of “mounts” being built around the nest entrance and sometimes chimney-looking structures.

Some ground nesters from Maryland

Andrena vicina – The neighborly mining bee

This is a relatively large (~1-1.5cm) bee, which received that cute name because it builds communal nesting areas (“neighborhoods”). In Maryland, the species is active in June/July and is generally seen visiting many native plants and crops. In particular, this is one of the known visitors of, among other plants, Rhododendron and Azaleas, several heather family plants (like Vaccinium, Kalmia), as well as several rose family plants (Prunus, Rubus).

Augochlorella aurata – Golden sweat bee

This is a species in the Halictid family, and is called sweat bee because it is often found collecting sweat (for water and salts). This is one of those tiny bees that you may find landing on you on a hot day, really committed to not letting go of your skin! This particular bee is small, metallic-looking, with beautiful green/golden iridescence. The species displays primitive eusociality, meaning that there is a queen that starts a nest, and across the season, generations of first infertile and later fertile workers are produced. By the end of the season, the fertile workers are inseminated and disperse to overwinter. This bee species is pretty generalist in its choice of plants, known as a pollinator of many crops (e.g., apples, tomatoes, watermelon) as well as native plants.