The red imported fire ant, Solenopsis invicta (Buren) (Hymenoptera: Formicidae), is abundant in cotton throughout much of the southern United States. This voracious predator reaches extremely high densities and may have widespread effects on other arthropods in cotton. We conducted a two-year sampling study and a series of greenhouse and field experiments to document the impact of red imported fire ants on beneficial insects in cotton. We found that the density of 12 out of 13 natural enemies sampled on cotton plants in 1999 and eight out of eight sampled in 2000 were negatively correlated with the density of foraging fire ant workers. We found that red imported fire ants reduced the survival of ladybird beetles (Coccinella septempunctata and Hippodamia convergens) by 50% and green lacewing larvae (Chrysoperla carnea) by 38% in greenhouse experiments. Fire ants did not, however, reduce the survival of spiders (Oxyopidae, Thomisidae, and Clubionidae). We used a commercially available fire ant bait to suppress fire ant populations in cotton fields during the 2000 growing season and compared the densities of beneficial arthropods in treated versus control fields. Densities of ladybird beetles and big-eyed bugs were significantly higher in fields with reduced fire ant populations than in fields with relatively large fire ant populations. The effects of fire ants on the abundance of minute pirate bugs, damsel bugs, and hooded beetles were more complicated, but their overall abundances were higher in control fields than in fire ant suppressed fields. The results of this study suggest that red imported fire ants are major intraguild predators of several important biological control agents and emphasize the possibility of ants as intense intraguild predators in cotton.