Nesting aggregations are often extensive (containing several thousand nests) and have been encountered in a variety of sites, such as grassy slopes, coastal cliffs, roadside verges and gardens. In October 2006 immense numbers of nest burrows were seen in a number of adjoining gardens in Tisbury, Wiltshire. These were excavated both on lawns and in side beds (pers. obs). O’Toole (pers. comm.) found a dense nesting aggregation in Guernsey in a low earth bank above the beach, well within the spray zone. On the Channel Islands the bee is sometimes considered a pest, as numerous females excavating their nest burrows in roadside banks can lead to slumping of the soil (C O'Toole, pers. comm.).

Males, which generally far outnumber females, occasionally settle to inspect open burrows and, within very dense nesting aggregations commonly attempt copulation with each other. When female bees emerge from burrows they are often pounced upon by a number of males forming conspicuous mating clusters. Most females mate immediately on leaving their nest entrances. There they attract the attention of males that are awaiting such an event. This was demonstrated in dramatic fashion at Brownwich Cliffs, a coastal site on Southampton Water, Hampshire, in September 2010 (G R Else pers. comm.). A huge number of males were flying about the sandy cliff face though no females were immediately obvious. From time to time mating clusters would tumble down the cliff and come to rest on the more or less level ground at the base. There more males would join the cluster. Somewhere in the center was a freshly emerged female that had coupled with one of the males. After some minutes the mated pair would extricate itself and the bees would fly off in tandem. Some clusters, however, consisted only of males, perhaps as many as two dozen. Saxton (2009) describes in detail the sexual behaviour of this species near Hastings, East Sussex.

Bischoff, Eckelt and Kuhlmann (2005) studied in some detail the nesting biology of C. hederae in Germany. They found that nesting females utilised old nests and also dug new ones. Four nest burrows of this bee were excavated and studied by these authors. These first ran between 7-12 cm horizontally into a steep face, before turning downwards. The cells were located at a depth of 30-45 cm. Groups of up to four cells branched directly off the main vertical burrow and in most instances side branches were absent.