We conducted a statistical evaluation of the pattern characteristics used to distinguish juvenile and adult copper-bellied (Nerodia erythrogaster neglecta) and yellow-bellied (Nerodia erythrogaster flavigaster) watersnakes. A total of 405 preserved museum specimens (juvenile = 242; adult = 163) was grouped as either neglecta, flavigaster or intermediate based on previous evaluations of the geographical variations of pattern seen in these taxa. Depending on the nature of the character, its state was either scored across its phenotypic range or measured using digital image analysis techniques. The juvenile neglecta and flavigaster phenotypes are consistent with their historical descriptions and the intermediate phenotype is nearly identical to neglecta. The amount and intensity of the dorsal pigment invasion of the ventral scales was the most informative adult charter. Digital image analyses of these characters are consistent with their historical descriptions for the neglecta and flavigaster phenotypes. For the intermediate phenotype, the amount of invading pigment was consistent with the neglecta phenotype, whereas the intensity was consistent with the flavigaster phenotype. The results of this research may provide a more objective means of identifying populations of the Federally threatened N. e. neglecta.