The nesting behavior of >300 females of Oxybelus bipunctatus was studied for 15 straight weeks in a sandpit in central New York during late spring-summer 1985. Cool and rainy weather in late spring induced moldy conditions in the cells that caused much larval mortality. Successive generations of wasps emerged in the field and laboratory every four to six weeks. Cells were always excavated in moderately damp sand. Cell depth varied inversely with soil moisture as tied to the amount of rainfall. Female cocoons were larger and heavier than male cocoons, but they did not occupy deeper or shallower cells. One-celled nests were predominant in this species. The number of prey per cell was rather uniform throughout the nesting season despite much variation in the prey fly families. Individual and aggregate prey weight per cell decreased slightly through the summer. Male Cyclorrapha were preyed upon more than any other taxon.