Variation at allozyme loci provided the first insights into levels of genetic variation in natural populations. Due to the large number of alleles found at most loci, allozyme alleles were originally thought to be neutrally-evolving markers of genetic diversity; allozyme allele frequencies were subsequently used extensively in systematics. Many recent studies, however, have provided evidence that natural selection is acting on individual loci in certain species, while others have supported neutrality. Here we provide evidence that natural selection is acting on the Idh-1 allozyme locus in the striped ground cricket, Allonemobius socius. This species provides an ideal model system in evolutionary biology due to its large geographic range and the natural phenotypic, life-history, and genetic diversity which occurs across its range. Geographic allele distributions, environmental data, fitness phenotypes, sequence analyses, and preliminary enzyme kinetic data for Idh-1 are presented.