Male African dwarf frogs have small glands behind their front arms, while females lack similar structures. Called post-axillary subdermal glands, they resemble small pimples. These glands likely serve a reproductive purpose, but their function is not yet clear.
According to David Cecere of Dwarf Frog Central, there are two other clues that can help you tell whether you have a male or female African dwarf frog. Males are the gender that sing, buzz or vocalize. This is done to attract mates as it is in most frog species. Additionally, females grow larger than males do and often have a belly full of eggs, which gives them a pear-shaped appearance.