If you find a black and white bee in the garden it’s a good chance it’s an Ashy Mining-bee, Andrena cineraria. This is a striking beast, and one I’ve not found in the garden before. The female has two broad white hair bands across the front and hind of the thorax, and the abdomen is very dark and glossy with a slight blue-black hue. The male, although fairly similar, is less distinctive, but still has the dark blue-black look with abundant white hairs.
There is a single flight period each year, and can be found from early April until early June. The males emerge before the females. Peak activity coincides with the flowering periods of fruit trees such as Pear, Cherry and Apple. But as a whole this is a ‘polylectic’ species, meaning that they visit a large number of different plant species to collect pollen and nectar. The Lady’s Slipper Orchid, Cypripedium calceolus, is predominantly pollinated by A. cineraria, and other solitary bees of the Adrena genus. Its survival may be dependent on a thriving solitary bee population.
Andrena cineraria nests are constructed in the ground, and the nest entrances are surrounded by a volcano-like mound of excavated spoil. Nests are often in dense aggregations in lawns, flower beds, mown banks and in sparsely vegetated field margins. The bee is common in gardens, parks, calcareous grassland, orchards and on the edges of cropped agricultural land. The entrance is no wider than a small pencil and can be 10-20cm beneath the ground. Here the individual nests will contain a few cells that are provisioned with pollen and nectar. Each cell will contain a single egg and then be blocked off. The female will only live for a few weeks. The eggs hatch a few days after being laid and the larvae grow, feeding on the pollen and nectar stored within the cell. The larva pupates within a few weeks but then hibernate until the next spring to start the cycle over again. I’ve had a look around the garden but can’t see any evidence of nests, so perhaps this female was passing through.
Although these are solitary bees, in that each female makes its own nest, they are sociable, with many nests close together often in dense aggregations. The burrow entrance is left open during foraging trips, but at the end of these flights, during rain and when disturbed the burrows are closed. A. cineraria plays host to the cleptoparasite cuckoo bee Nomada lathburiana. The female Nomada seeks out open cells of A. cineraria that are still being provisioned with food and lays its egg before the host lays her egg and seals the cell. The Nomada larva tends to hatch first and kill’s off the egg or larva of the host Andrena, and then feeds off the provisions laid down in the cell.
Andrena cineraria is widespread throughout Europe and is common from Ireland eastwards across central Europe and into Scandinavia. It is more restricted, but still widespread in the Mediterranean region. In the UK the distribution seems to fall off the further north, with a few records in western Scotland.