Ground nesting bees in your backyard!

 

Not all bees live in hives like honey bees do. In fact, 70% of all the 20,000 species of bees nest under ground.  In North America, most of these ground bees become active in early spring. Nests of these bees are easy to identify above ground because of the conical piles of dirt with a large hole in the middle that serves as the entrance to the bee burrows (Photo 2).

One of the most abundant ground nesting bees in northeastern and midwestern region of North America is Colletes inaequalis (photo 1). Even though this bee is solitary, meaning that every individual female builds her own nest, it is also a gregarious nester (photo 2). Many females (hundreds and sometime thousands) build their nests next to each other. The nests are obvious above ground because of the conical piles of dirt with a hole in the middle (photo 2). Colletes inaequalis has a strong preference for sandy soils on south facing slopes. Thus, if you have these conditions in your backyard, you may find these bees showing up every year where you live. Unlike social bees and wasps, solitary species are not aggressive insects even though females do have sting. These bees will not attempt to sting humans unless handled. Most activity at nest sites in early spring is of males looking for females to mate with – male bees cannot sting (photo 3).

Besides C. Inaequalis, many other ground nesting native bees can be found in your backyard. For example, species of the bee genera Agapostemon, Andrena, Halictus and Lasioglossum are also very abundant in North America (photo 4 - 6). All of these native bee species provide important ecological services that include pollinating many of the plants in your garden and nearby. Specifically, Colletes inaequalis and similar looking Andrena species are important pollinators of spring crops like apples, blueberries and cherries. Therefore, we do not consider these bees as pests and strongly recommend avoiding the use of chemicals to control them. Pesticides are bad for humans and beneficial insects. Usually, using water over the area of the nest is enough to encourage the bees to look for a different nesting area. However, due to their beneficial role as pollinators and their lack of aggressive behavior, please consider maintaining these important bee pollinators in your backyard! 

Photo 5: Andrena sp. female excavating soil

Credit: Jason Gibbs

 

Photo 6: Halictus ligatus female next to a larva on top of a pollen mass

Credit: Jason Gibbs

Photo1: Colletes inaequalis female

Credit: Margarita López-Uribe

 

Photo 2: Colletes inaequalis nest aggregation

Credit: Margarita López-Uribe

Photo 3: Colletes inaequalis males around a female

Credit: Jason Gibbs

Photo 4: Agapostemon sp. female at the entrance of her nest

Credit: Laura Russo