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This study is the first to combine both field and genetic data to examine population structure in flightless beetles from the Galapagos Islands. Field studies were conducted on four species of tenebrionid beetles belonging to three genera, Ammophorus Guerin-Meneville, Blapstinus Latreille, and Stomion Waterhouse. The dynamics of the beetle community at the study site, Tortuga Bay, Santa Cruz Island, were analyzed in an attempt to examine patterns of activity and to quantify species abundances, population sizes, densities and levels of individual vagility. Beetle activity was found to vary with temperature, precipitation and number of sunlight hours. Although the number of recaptures was low, densities in the quadrats ranged from eight B. lugubris Boheman per hectare to 1238 S. laevigatum Waterhouse per hectare. Individual vagility is shown to be low among S. laevigatum, the most abundant species at the study site, as the dispersion index (DI) showed that captures were aggregated in three of the four quadrats, suggesting little movement. In addition, beetle captures occurred more frequently than expected in internal traps, again revealing limited movement into or out of the quadrats. These results were confirmed by a separate analysis of genetic differentiation among demes of S. laevigatum which showed the number of migrants to be less than one per generation.