Bait particle size preferences of six ant species among four particle sizes (2.36, 2.0, 1.44, and 0.85 mm) were determined in laboratory assays. Based on weight of bait particles removed over a 3-h observation period, Solenopsis invicta Buren Aphaenogaster fulva Roger and Aphaenogaster lamellidens Mayr preferred the 2.36 mm bait particles. Formica pallidefulva Latreille workers equally preferred the 2.36 and the 2.0 mm particles. Linepithema humile (Mayr) equally preferred the 2.0 and 1.44 mm particles while Pheidole dentata Mayr preferred the 0.85 mm particles. Particle size preference in these assays was positively correlated with mean width of the head capsules of the worker ants. These results suggest that particle size of formulated baits might be matched with ant species to improve efficacy against targeted pest ant species while minimizing impact to nontarget native species. Competitive interactions of the invasive S. invicta with the four native ant species (A. fulva, A. lamellidens, F. pallidefulva, P. dentata) in this study showed that S. invicta workers rapidly dominated foraging areas and subsequently raided nests of the native ants.