You cannot determine the sex of a fire-bellied toad from its appearance outside of the breeding season. Breeding males develop black nuptial (mating) pads on the insides of the thumb, second finger, and forearms, as well as on the feet. You could also determine the gender by noting a firebelly's behavior: only the male makes sounds. When looking for a mate the male will be the one jumping onto the back of other toads. (If he jumps on another male, the mistaken firebelly will let out a special croak.)