Extrafloral nectar, a solution of both sugars and amino acids that is produced by plants on stems and leaves, attracts ants that often protect the plants from potential herbivores. To understand better the ecological significance of variability among plants in nectar chemistry, the effectiveness of ant attraction by different extrafloral nectars was compared for nectar mimics that varied in either amino acid or sugar content. Workers of the fire antsSolenopsis invictaBuren andS. geminata(F.) were fed on artificial nectaries containing mimics of pre- and postdefoliation nectars ofImpatiens sultani, which differed in amino acid content. Workers of the two fire ant species also fed from artificial nectaries containing mimics ofPassiflora ambigua,P. talamancensis, andP. quadrangularis, which varied in sugar composition.S. geminataworkers preferred the more amino acid-rich postdefoliation mimic over the predefoliation mimic.S. invictadid not discriminate between the two nectars, demonstrating that richer amino acid solutions are not more attractive to all ants. In the sugar experiments, both species of ants preferred the nectar ofP. ambiguaover those of the other twoPassifloraspecies. The nectar ofP. ambiguahad the lowest total sugar concentration and the lowest calorie content, indicating that ants do not necessarily maximize sugar energy intake as they forage. The behavior ofS. geminataandS. invictashows that both amino acid and sugar content can affect ant recruitment to plants and that differences in levels of recruitment cannot be predicted accurately based on simple assumptions of nutrient maximization or energy content.