Peter Lembcke is currently writing a caresheet for N. maculosus. This is what he says:
"Gender in N. maculosus can be determined by examining the vent of the animal. During the breeding season, males will have a swollen cloaca, as well as a pair of nipple-like papillae at the rear of the vent (Sajdak, 1982). Females may have lighter coloration around the vent."