Females often show a black triangle at the abdominal apex (tip). In temperate areas, Andrena bees (both males and females) emerge from the underground cells where their pupae spend the winter, when the temperature ranges from about 20°C to 30°C. They mate, and the females then seek sites for their nest burrows, where they construct small cells containing a ball of pollen mixed with nectar, upon which an egg is laid, before each cell is sealed. Andrena usually prefer sandy soils for a nesting substrate, near or under shrubs to be protected from heat and frost.  --From Wikipedia