It can be pretty difficult for the average person to guess the sex of a frog, just by looking at it. Also, most frogs have internal reproductive organs, you can’t just pick up a frog and look at its reproductive organs to tell whether it is male or female. However, in most frog species, there are few characteristics you can use to tell apart males from females.
In general, you can tell male from female frogs’ in most species by observing the body size, vocalization, the vocal sac, and mating behavior, among other things. In many frog species, males are on average smaller than females – and only males have vocal sacs and make mating advertisement calls.
In some species body size alone is not an effective way of differentiating male from female frogs’. For example, in the black-striped frog (Sylvirana nigrovittata) found in some parts of Asia, females are larger than males on average, but there is considerable overlap in size.
In these frogs’, it’s possible to find males that are similarly sized, or even larger than some females.
Also, although female frogs’ typically do not make advertisement calls, those of a few species do.
How To Determine The Sex Of A Frog
The best way to distinguish male from female frogs’ is to first determine the species you’re dealing with.
Once you know the frog species, you can then look for traits that are specific to one sex in that species.
Here’s how you can tell whether a frog is male or female:
1. Listen To The Vocalization
The females of most frog species lack or have only rudimentary vocal cords, and do not call to attract mates.
The typical loud calls (croaking) that we hear frogs make are known as advertisement calls- it’s male frogs advertising themselves as potential partners, hoping that female frogs’ will like their song and come their way.
These distinctive sounds range from high-pitched peeps to full-throated croaks.
Males usually call from ponds, swamps, streams, and other possible breeding sites. Each frog species has a different call and female frogs’ will only be attracted to the call of their own species
When females are ready to mate, they will move towards calling males, and pick the male that they prefer.
Female frogs’ are generally considered to be the quieter sex. However, this is not to say that female frogs can’t make any noise – they certainly can.
Frog vocalization is not just used to attract a mate. Other types of vocalizations include territorial calls, release calls, distress calls, and warning calls.
However, these calls are not as frequent, or as loud as advertisement calls. If you ever hear a frog croaking loudly, chances are, it’s male.
2. Look For The Vocal Sac
Frogs have simple vocal cords that have two slits in the bottom of the mouth. They also have a vocal sac that can amplify the vibrations from the vocal cords.
In almost all frog species, only the males have a vocal sac.
When calling, a frog closes its mouth and nostrils, and expels air from its lungs through the vocal cords and into the vocal sacs. The vibrations of the vocal cords emit a sound – and the inflating and deflating vocal sac makes the sound louder or quieter.
By forcing air back and forth between their vocal sac and their lungs, the call becomes rhythmical.
The vocal sac is an elastic membrane of skin. It acts as a resonating chamber, causing the male frogs’ mating call to be amplified and carry significant distances.
Most frogs’ have a single vocal sac under their throat, whereas other frogs have the vocal sac on the corner of their mouth.
When a frog calls, the vocal sac will expand, but its mouth won’t open. Sometimes, it may look like the frog staring off while making the sound.
When not calling, the vocal sac of a male frog will appear as loose skin on the throat, and is often a different color than the rest of the belly.
In comparison, the throat of female frogs’ Will not have any loose skin, and will have a coloration that matches the belly.
3. Look At The Body Size
In more than 90% of frog species, females are larger than males on average. However, there is a considerable overlap in size in some species, so it’s possible to find similarly sized male and female frogs’.
Still, in most instances, female frogs tend to be on the larger side, and males on the smaller side.
Female frogs’ are responsible for carrying eggs, so their larger size allows them to hold more eggs.
In many frog species, female fecundity (capability to produce offspring)is positively correlated with size, so large females may lay more eggs than smaller females of the same species.
For example, female Cuban tree frogs’ (Osteopilus septentrionalis), typically lay between 100 – 1000 eggs at a time. However, large females can lay more than 15, 000 eggs in one breeding season.
The females of many frog species take longer to reach sexual maturity than males. This allows them to breed at a larger size and produce more eggs.
4. Look At The Mating Behavior
In the breeding season, male frogs’ arrive first at the breeding sites and call to attract females. Once the females arrive, the males will try to grab them from behind in a tight mating embrace called ‘amplexus’.
In almost all species, the males are always the ones on top. If you ever see a pair of mating frogs’, you can be sure the one on top is male.
Community Science with the Harris Center (CC BY-NC 2.0)
5. Look For Nuptial Pads On The Hands Or Thumbs
Male frogs’ of many species have differently colored and/or more roughly textured patches on their hands, especially on the insides of their thumbs. These patches of skin are of textured skin are called nuptial pads.
Most times of the year, these nuptial pads may be tricky to see, however during the breeding season, they often turn dark and become raised.
The nuptial pads help the male frog securely cling to the female during the amplexus embrace.
Among North American anurans, nuptial pads can be observed in males of:
- True frogs’ of the frog family Ranidae
- True toads of the family Bufonidae
- Spadefoot Toads of the family Scaphiopodidae
They can also be observed in Cuban tree frogs’ (Osteopilus septentrionalis).
That said, nuptial pads aren’t a good indicator of sex for all species. For example, many tree frogs’ in the family Hylidae, such as the gray treefrog (Hyla versicolor), do not have nuptial pads.
Also, if you find one of the frogs that do nuptial pads, and it doesn’t have them, it could still be male.
The nuptial pads only appear in sexually mature males, so a frog lacking nuptial pads might be a female frog, or it might be an immature male.
6. Look At The Size Of The Tympanum
In a few frog species, the sex can be identified by the size of the external hearing structure, known as the tympanum.
The tympanum is a large external oval-shaped membrane located just behind the eye. It transmits sound eaves to the inner parts of the frogs’ ear, which is protected from the entry of water, and other objects.
In some frog species, males have a significantly larger tympanum than females.
A few of these species include:
- American bullfrog (Lithobates catesbeianus)
- Green frog (Lithobates clamitans)
- Bronze frog (Lithobates clamitans clamitans)
- Mink frog (Lithobates septentrionalis)
- Carpenter frog (Lithobates virgatipes)
- River frog(Lithobates virgatipes)
- Pig frog (Lithobates grylio)
The males of these species have tympana that are roughly twice the size of their eyes, whereas the females have tympana that are about the size of their eyes.
In most other frog species, both males and females have a similar-sized tympanum – about the size of their eye.
7. Look At The Coloration Of The Body
In most species, both male and female frogs’ are the same color. However, a few frog species exhibit sexual dichromatism, in which males and females have different colors.
Yosemite Toad (Anaxyrus canorus), is an example of a sexually dichromatic frog species. Male Yosemite Toads have a yellow-green to olive coloration, while females have gray, tan, or brown coloration with black spots.
Here’s a table that details a few sexually dichromatic frog species:
Frog Species |
Nature Of Sexual Dichromatism |
| Moor Frog (Rana arvalis) | Breeding males have a blueish coloration |
| Wood Frog (Rana sylvatica) | Breeding males are darker than females |
| Mink frog (Lithobates septentrionalis) | Females have dark pigmentation in a reticulated pattern |
| European Common Frog (Rana temporaria) | Breeding males have a grayish coloration |
| American Toad (Anaxyrus americanus) | Males are generally yellower than females |
| Western Toad (Anaxyrus boreas) | Males are generally less spotted than females |
Internal Differences Between Male And Female Frogs
Male and female frogs’ have different genitals. However, these genitals are housed within the body, so you can not just pick up a frog and examine its genitals to identify its sex.
Still, if you had a chance to dissect a frog, it would have two interior testicles and a spermatic canal, if it were male. If it were female, it would have ovaries and oviducts, as well as a uterus that stores the eggs until they are laid.
Sources:
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Méndez-Tepepa, M., Morales-Cruz, C., García-Nieto, E. et al. A review of the reproductive system in anuran amphibians. Zoological Lett 9, 3 (2023). https://doi.org/10.1186/s40851-023-00201-0
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