Nesting aggregations, which are sometimes very large, occur in bare soil (e.g. surfaces exposed by land slippage), in artificial mounds of soil, and even in the sides of rabbit burrows. Nesting sites may be subject to occasional inundation by the sea. A nesting aggregation at Scolt Head Island, Norfolk, was reached by the highest spring tides, and the bees were observed trying to reach their burrows, which were submerged in about 7 cm of water (Field & Foster, 1988). On the Norfolk coast, bees have been seen emerging from waterlogged mud (D B Baker, pers. comm.). The nest architecture is similar to that of C. succinctus and has been illustrated by O'Toole and Raw (1991): a cluster of five to six cells radiates from the end of a short, curved burrow. Males may occasionally be found roosting in groups of up to a dozen on grass stems (P Kirby, pers. comm.).