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Yellow jackets (Hymenoptera: Vespidae) are attracted to the typically ant-dispersed seeds of trilliums and will take seeds from ants in the genus Aphaeogaster. To determine if yellow jacket, Vespulla maculifrons (Buysson), presence interferes with seed foraging by ants, we presented seeds of Trillium discolor Wray to three species (A. texana carolinesis Wheeler, Formica schaufussi Mayr, and Solenopsis invicta Buren) of seed-carrying ants in areas where vespids were present or excluded. We found that interspecific aggression between yellow jackets and ants is species specific. Vespid presence decreased average foraging time and increased foraging efficiency of two of the three ant species studied, a situation that might reflect competition for a limited food source. We also found that yellow jackets removed more seeds than ants, suggestive that vespids are important, albeit underestimated, components of ant-seed mutualisms.