Each of the three grasshopper species, Camnula pellucida, Melanoplus bilituratus and M. bivittatus, spent approximately 13, 17, 19, 22 and 29% of total time in nymphal development in the successive five instars. These proportions appeared similar at each of the six rearing temperatures 75, 80, 85, 90, 95 and 100°F. The times required for total nymphal development at these temperatures were 53, 36, 28½, 23½, 18 and 17 days, respectively. It was estimated that, for the grasshoppers to complete nymphal development and attain sexual maturity in time to have a reasonably good chance of successful reproduction, their integrated temperature experience for 12-hour days should be not less than 95°F. Whereas the apparent mid-point of nymphal development in terms of morphogenesis is midway through the third instar in the typical five-instar grasshoppers, the midpoint of time spent at constant temperatures is near the end of the third instar. C. pellucida appears unable to complete nymphal development at a temperature as low as 75°F.; the Melanoplus species, however, can complete development at this temperature, but with reduced survival.