1. Temporal constancy in the structure of grasshopper assemblies (about forty-five species each) from two types of North American grasslands was assessed; one site was followed 25 years and the other 7 years.
2. Densities and relative abundances varied but composition of assemblies based on ranks suggested significant structure when three or more species were included in the analysis.
3. Results compared favorably with other insect herbivore assemblies which have been examined; variability in population change was intermediate along the spectrum of organisms which have been studied