Studies made at the Wisconsin Experiment Station in 1924-1925 show variations, partly correlated to temperature, in the period from egg laying to capping of worker brood cells from less than 8 days to more than 11 days, majority being capped between the 8th and 9th days. Variations for complete development ranged from less than 19 7/8 days to more than 24 days. One set of experiments showed approximately 75 per cent of 4094 workers completing their development in less than 21¼ days. In another more definitely controlled set of 2602 individuals, 94 per cent emerged in less than 21 days with an average developmental period of approximately 20½ days.