How to Sex Every Animal-Edition II: Amphibians!

-Frogs and Toads. Frogs and toads have several different methods of being able to distinguish males from females, depending on the species and/or taxa. Most are generally sexually dimorphic in size, with females being much larger than males, although there are always exceptions. Males can also sometimes be distinguished by the presence of their vocal sacs, which may either appear as more thinly lined and baggy appearing areas around the throat, or can sometimes be differently or more brightly colored in males than females. Male frogs of many species can also have much larger tympanic membranes, or the flat, “ear-like” discs on the sides of their heads behind the eyes, which are typically only equal to or smaller than the sizes of the eyes in females. Some groups of frogs, such as the dart frogs (dendrobatids) and mantellas, have larger toe pads in males, and other sexually dimorphic characteristics such a more prominent dorsal arch in females, and larger overall size, length, or girth in females compared to males.

*Figure 1. Comparison of Typanic Membranes in American Bullfrogs, female (A), and male (B). Credited to Peter M. Narins, et. al.

*Figure 2. Example of a modified appendage, in this case, the Nuptial Pad, seen in male anurans (right), but absent in females (left). Credited to Frog Forum.

Males of many species can also have modified spines, nuptial pads, or other modified appendages on their front and/or hind feet used for mating and amplexus, or sometimes thicker and muscular fore-limbs for the same purpose. Finally, many frogs and toads can display sexual behaviors more likely indicative or males, such as constant croaking or vocalizations relative to females, and/or greater willingness to perform amplexus behavior. Frogs and toads are typically extremely difficult, if not impossible to otherwise sex in their younger, or tadpole forms before sexual maturity, at least not without more advanced techniques.

*Figure 3. Example of Sexual Dimorphism in size, length, and girth between male and female Dart Frogs. Credited to Josh’s Frogs.

-Salamanders, Newts, and Other Caudates. Salamanders and newts have several different methods of being able to distinguish males from females, depending on the species and/or taxa. Most are generally sexually dimorphic in size, with females being much larger than males, although there are always exceptions. Males of many species can also have modified spines, nuptial pads, or other modified appendages on their front and/or hind feet used for mating, or sometimes thicker and muscular fore-limbs for the same purpose. Finally, look for oftentimes, larger and more pronounced cloacal bulges near the hind limbs and tail in male salamanders or newts when compared to females. Salamanders and newts are typically extremely difficult, if not impossible to otherwise sex in their younger, or larval forms before sexual maturity, at least not without more advanced techniques. Some species, or intermediate life stages such as efts, can be very difficult to impossible to sex outside of their breeding seasons. Some species of newts can also have genital glands, submaxillary glands, or mental glands on the sides of the head or throat as well.

*Figure 4. Example of the Cloacal Bulge in Salamanders between males (top) and females (bottom). Credited to Michael Benard.

-Caecilians. Caecilians are a bizarre and lesser studied group of amphibians, in which for many species, sexing is not possible through visual or external means, and males and females appear identical. Some of the aquatic members (the Typhlonectids) can be visually sexed however by examining the widened cloacal disks of males when compared to the more narrow, slit-like and elongated cloacal disks. Only mature adult caecilians, in any event, can be reliably sexed, if doing so is possible.