Females of this bee build clusters of oval cells from masticated leaf pulp on the undersides of rocks overlying shallow depressions. When freshly constructed the cells are probably bright green but, with time, assume a dull brown colour and then closely resemble rabbit droppings. The number of cells per rock varies from one to about 230, but large numbers either result from several females working independently of each other in a single season, or from several generations of females. Rearings from nests collected at the Blair Atholl site mentioned above suggest that in Britain this bee has a minimum two-year life cycle, the first winter being passed as a prepupa, the second as a diapausing adult within its cocoon. Some individuals may emerge from their nests three or four years after their cells were sealed (see Smith, 1851b). Such a staggered emergence could be important in northern Britain, where prolonged, inclement early summer weather could seriously hinder the activity of this bee.