Three nests of Crabro tenuis were studied during June 1971-1972 in Oswego County, New York. Females constructed shallow but lengthy, multicelled nests in sand with the cells being built in clusters, sometimes in series. Females plugged the entrances with damp sand and occupied the burrows during midday. Paralyzed prey were stored head inward at the end of the burrow. The deeper cells in a cluster were excavated and provisioned first and the shallower cells built and stored later, as determined by the developmental stages of the wasps within the cells. From four to seven paralyzed, adult male flies were placed in a fully provisioned cell with their venters toward the center. Such a cell usually held only one species of fly. Provisions consisted of the suborders Brachycera and Cyclorrhapha and comprised the families Rhagionidae, Anthomyiidae and Tachinidae. An egg was affixed about equally to the left or right side of the neck of a fly and this prey was placed against or near the wall of the cell. The nesting traits of C. tenuis were compared with those of other members of the Cribrarius group, C. advena of the Advena, group, C. venator of the Tumidus group and species in the Hilaris group
