Open dune systems are being degraded through human development and exotic species invasions. The Grand Sable Dunes, Pictured Rocks National Lakeshore, Michigan, are protected from development but not from the spread of exotic species. The invasive exotic spotted knapweed, Centaurea biebersteinii, has invaded significant portions of this dune system. Areas without spotted knapweed had higher native plant diversity than areas with spotted knapweed, as well as lower exotic plant diversity. Of native plant species occurring in the highest frequencies along transects in both spotted knapweed infested and non-spotted knapweed infested areas, four out of the five species were more likely to be encountered along transects in non-spotted knapweed areas than along transects in spotted knapweed areas. Insect families Curculionidae and Formicidae were captured more often in areas with spotted knapweed. Increased dune stabilization increased the ability of exotic plant species not adapted to the actively shifting sand dunes to invade and alter the plant communities. Differences in Curculionidae and Formicidae abundance were due to the changes in plant communities. Also, increased stabilization of sand dunes as a result of spotted knapweed invasion increased the abundance of Formicidae by increasing the stability of nest sites. Limiting the range of spotted knapweed in dune systems could maintain natural insect distribution and native plant diversity.