The Bullfrog is the largest frog in North America. The females grow larger than the males, up to eight inches. Bullfrogs vary in color, from dark olive to pale green above, and from white to cream underneath. They often have dark gray mottling (splotches) on their back legs. Bullfrogs have large eardrums behind the eye, and this is how to tell the male from the females. Males have larger eardrums, which will be bigger than the eye. Females have smaller eardrums, which will be the same size, or smaller, than the eye. You can tell a Bullfrog from other frogs, like the Green Frog or Pig Frog, by its lack of dorsolateral ridges. These are the two long lines down the back of most frogs.