The patterns of intraspecific genetic variation can be driven by large-scale environmental events or smaller-scale phenomena such as land clearing. In Australia, European farming techniques have altered the landscape by increasing the amount of arable farmland. We hypothesised that this increase in farmland would result in a concomitant increase in the effective population size of the black field cricket (Teleogryllus commodus). To test our hypothesis, we investigated genetic variation in 1350 bp of mitochondrial mtDNA and in two nuclear encoded loci, hexokinase and elongation factor 1-α, from 20 crickets collected at Smiths Lake, New South Wales. Molecular variation in T. commodus was characterised by an over-representation of singleton mutations (negative Tajima’s D and Fu and Li’s D) in all loci studied. Further, HKA tests do not suggest that selection is acting on any one gene. Combined, these data support the hypothesis that population expansion is the force driving molecular variation in T. commodus. If an increase in agricultural habitats is the cause of population expansion in T. commodus we hypothesise greater genetic subdivision in natural than farmland habitats. An alternative possibility is that the effective geographical range of the species has increased but the density at a given site remains unchanged.