Mining bees are wild bees that live underground
Once you start studying the pollinators in your garden, you will see many different types. If you start recognizing some of your visitors, you will look forward to seeing those old friends and indentifying new ones. People seem to care more about the things they can put a name to, so I encourage you to spend some time with identifications.
The different species within the genera are very difficult to discern, but most people can learn to identify down to genus. That in itself is an accomplishment!
For instance, take the genus Andrena. The 1300 species in this genus are also called “mining bees” because they nest in the ground. Like most bee species, they are solitary, which means that all females are fertile and each one builds a nest by herself, provisions the nest with pollen and nectar, and lays the eggs. Unlike a honey bee colony, there are no workers, no honey production, nor any comb building.
The eggs hatch and the young bees progress through the larval stage to the pre-pupal stage before winter sets in. During the winter they remain in the pre-pupal stage until early spring when they complete their metamorphosis into adult bees, both male and female. The adults emerge from the ground, mate, and the females of this new generation begin to build their homes in a new underground chamber.
Solitary bees are often oligolectic, and Andrena bees are no exception. An oligolectic bee is one that collects pollen from only a select few plant species. Often these plants are very closely related—in the same family or even the same genus. In fact, some species of Andrena bees are monolectic, meaning they collect pollen from one—and only one—species of plant. It is easy to see that if that plant becomes rare or extinct, so does its pollinator. No wonder our wild bees are in trouble!
Andrena bees range from about 8-17 mm long. The females in this genus can be distinguished from other bees by the velvety patch of hair between the eyes and the antenna bases. They also have well-developed corbiculae—or pollen baskets—on the sides of the thorax and hind legs. Since the males do not collect pollen, they are not as hairy as the females. The males are also shorter and narrower than the females.
Because Andrena bees build their nests underground, they are adversely affected by farming practices such as tilling, plowing, disking, and spading. They also do not thrive in ground that has been completely cleared of vegetation because they like nesting sites that are protected from weather extremes by bushes or trees. Heavy mulch is also bad for Andrena bees because the females are not able to dig through mulch to get to the soil.
Needless to say, insecticides readily kill Andrena bees and herbicides kill the plants on which they are dependent. Maintaining a pesticide-free garden with plenty of bare soil and many plant varieties—including native species—is the best way to attract and conserve most native bees, including Andrena.