Male and female fire-bellied toads look like twins to the untrained eye. Even to the trained eye many differences aren't obvious, and the amphibians themselves sometimes mistake male for female. Slight differences in physical characteristics, and behavioral and physical changes come mating season, give insight into what kind of fire-bellied toad you're dealing with. Note that while females and males will breed, aggression will not typically result from keeping two of the same sex.
Both female and male fire-bellied toads are generally covered in tubercles, which are wart-like bumps on their skin. Males tend to have more and better-defined tubercles on their backs; females usually have a smoother appearance. Some males have considerably more and larger tubercles than other males, leading to a very bumpy appearance, while some females have considerably fewer and smaller tubercles than other females, but you may also find fairly warty females and fairly smooth males.
While you might think your fire-bellied toad has four legs, his front legs are better known as forearms. The forearms females sport usually have a thinner appearance than the males'. It's a subtle difference, though. If you have a female and male next to one another, you'll likely spot it, but otherwise it's not a very telltale sign.
Once fire-bellied toads' breeding season arrives—typically in early spring—males develop nuptial pads, which the Smithsonian Institution National Zoological Park notes appear on their first and second fingers. Nuptial pads look like dark pads covered in what appear to be tiny thorns. These pads help the male fire-bellied toad hold onto the female when they mate. Females never develop nuptial pads.
Grasping and Mating
If you have two fire-bellied toads and one grasps onto the other, as if to mate, bank on whoever did the grasping being a male frog—females have no part in that behavior. But the frog who was grasped is not necessarily a female. Males often grab other males. Males who are grabbed will typically make a loud noise and twist and turn in an attempt to get away, but females may also do this if they're not ready to mate. Speaking of mating, males typically let out a mating call, especially during the breeding season, that the University of Michigan says sounds like a bark. Females may make noises if stressed, such as when picked up unexpectedly, but the barking-like call is usually a male-only feature.
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