Frogs are one of the few species that typically do not have sex organs outside their body, so telling the difference between male and female frogs externally is not immediately obvious. Still, there are ways to tell males from females without dissecting them. For example, most female frogs are larger than the males of the same frog species, with notable exceptions. Color, noises, and other features can also be used to tell the genders apart.
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Females are larger in most frog species
While people expect the males in an animal species to be larger than the females, in many frog species, females are larger than males. This makes it easier for male frogs to climb up on the female's back during mating. The size difference is not always large, however. Gray tree frog males range from 1.25 inches to 2 inches long, with females a bit bigger at 1.5 inches to 2.25 inches. So, although the size difference is there, you'd need to have a male and a female together to see that one is a little larger.
Males call to attract females
When you hear the sweet "ribbit ribbit" vocalizations of a frog, it's usually a male calling to attract females. Although female frogs can vocalize a bit, males have vocal sacs that enable them to croak especially well and repeatedly. Of course, this is a sound you hear rather than a specific frog you see vocalizing because any frog you're lucky enough to see will be more likely to freeze in fear or jump away quickly rather than sit still and sing for you. If you own a pet frog who croaks regularly, you can be almost certain that you have a male frog.
Males are on top when mating
If you see one frog on top of another frog, they are mating, and the male frog is on top. This position is ideal for the male to fertilize the eggs with his sperm as the female lays them, sometimes thousands at one time. Frogs can stay in this position for days or weeks until the female releases all the eggs. Since frog eggs must stay moist, frogs lay eggs during their area's rainy season. Sometimes, numerous frogs will lay their eggs together as a means of trying to ensure the safety of the eggs.
Compare colors and textures
Although males and females are the same color in many frog species, males sometimes change color. For example, the green tree frog is a dull green to grayish color, but males may appear to be bright yellow when calling out to females. In many tropical frog species, the males are brighter colors to begin with. As for texture, assume that frogs with smooth skin are females, while frogs with bumpy or spiky skin are males. In some frog species, like the Australian tree frog, the male's vocal sac is darker than the female's due to his frequent calling.
Exceptions to the norm
Just when you think you know how to tell the difference between male frogs and female frogs, you encounter some exceptions. Consider the American bullfrog, for instance, which is one frog species in which males are noticeably larger than females. However, males have bright yellow throat patches, while the female's throat patches are white. The "tailed" frog, which lives in the state of Washington, is the only frog species with an external sex organ, which is called a tail. Among smooth guardian frogs of Borneo, female frogs call just as much as the males.
Mysterious sex changes
For many years, scientists noticed that in polluted areas, male frogs developed external female genitals, but further research published in 2021 as reported in National Geographic found that such changes occurred in nonpolluted ponds just as often. Researchers studied 18 Connecticut ponds, some with chemical pollution and others in pristine forests, and found that as much as 10 percent of the frogs had changed in equal numbers from male to female or female to male. Such changes occur in the tadpole stage; adult frogs cannot change genders.