Andrena is a genus of solitary bees, which means the females build nests and care for broods alone. Some species are sub-social. In other words, females provide prolonged care to their larvae, as opposed to sealing up the nest with the food source. Mining bees are named after their nesting behaviour. They dig tunnel-like burrows in sandy, clay or loam soils, in which they lay their young. It's not unusual to see hundreds of mining bee nests clumped together in the same spot because females don't seem to mind a neighbour or two. It's thought that this is because having multiple nests in one place will decrease the total number of nests parasitised or predated. Andrena tend to be concentrated in temperate climates. There are only 14 recognised species in Africa, concentrated to northeastern parts of the continent.