We observed agonistic behavior among larval Ambystoma opacum, A. jeffersonianum, and A. maculatum in intra- and interspecific pairwise comparisons to determine if sympatric species exhibit unique behavioral responses to the presence of con- or heterospecific larvae, if they respond similarly to variation in competitor size, and if species identity is a reliable predictor of predation and cannibalism versus strictly nonlethal competitive interactions as an outcome of larval aggression. Each species exhibited a unique suite of behavioral responses associated with species and competitor size. Ambystoma opacum displayed high levels of aggression, most often towards conspecifics, but these behaviors rarely resulted in predation. Conversely, A. jeffersonianum displayed aggression frequently and often consumed both con- and heterospecific larvae. Furthermore, this species did not reduce aggression even in the presence of larger larvae. Ambystoma maculatum displayed relatively low levels of aggression under most circumstances. We conclude that these characteristic responses are associated with species-specific morphological and developmental features and the temporally staggered pattern in which these species appear in ponds. These observations highlight the importance of these traits to behavioral divergence among ecologically similar taxa occurring in sympatry.