Spotted knapweed, an exotic plant that has invaded much of the western United States and Canada, alters environmental characteristics and severely reduces native plant diversity and abundance. To investigate impacts of spotted knapweed on savanna communities we initiated a study comparing ground beetle (carabid) diversity and abundance in invaded and un-invaded sites. Environmental variation is important in shaping carabid species assemblages, and in turn changes in abundance and distribution of particular species can indicate changes in environmental conditions. There was no significant difference in species richness and evenness between invaded and un-invaded sites; however, when species were delineated into trophic groups evenness was significantly higher in un-invaded than invaded sites. Indicator values were calculated for all species based on a typology of five clusters. Species assemblages clumped by environmental tolerances. Comparison of indicator species biologies to site and/or site grouping characteristics and results from non-metric multidimensional scaling reveal that carabid assemblages are primarily shaped by soil texture and moisture, and the abundance of spotted knapweed. Indicator species among invaded sites differ dramatically in their described tolerances to soil texture and moisture, however, they related to each other in preference to spotted knapweed. Analyses of carabid trophic structure and indicator species in invaded and un-invaded sites reveal that spotted knapweed affects carabid distribution and simplifies trophic complexity of invaded sites.