The author describes an aggregation of Andrena argentata in the dunes of Schoorl; he mentions two strategies of mating, tells where the females get their pollen from heather and observes the lack of brood parasites at this site. He comes across Nomada baccata as probable brood parasite at another site where the nests of A. argentata are more spread out. The author describes the nest-building of Colletes succinctus and compares his findings to the standard litarature. O’Toole en Raw describe nests that are quite different. The behavior of the sarcophagid fly Miltogramma punctata in relation to Colletes ♀ is described. Five larvae – presumably of this fly – are found in an excavated brood cell of Colletes. But the rearing of these larvae was not succesful.