Toads, members of the amphibian order Anura, present a challenge when determining their sex outside of the breeding environment. Toads exhibit subtle sexual dimorphism, meaning the physical variations between males and females are often minimal or only appear seasonally. Identifying a toad’s sex requires careful observation of several physical and behavioral traits, moving beyond simple visual inspection to include specific anatomical checks.
General Physical Indicators of Sex
One frequently observed difference between the sexes is size; females are typically larger and heavier than males, a pattern called reversed sexual size dimorphism. This size disparity allows the female to produce a greater number of eggs, increasing reproductive output. A female toad may also appear noticeably rounder or more inflated, especially when she is gravid (carrying mature eggs).
The coloration of the throat is another indicator, particularly in species where males vocalize extensively. In many male toads, the skin covering the vocal sac beneath the chin develops darker pigmentation. This area often appears gray, black, or deep yellow due to an increased concentration of melanophores. Female toads usually retain a lighter, often white or mottled throat color that matches the rest of their ventral skin.
Subtle variations in skin texture can also hint at a toad’s sex, though this is highly species-dependent. Some male toads display rougher skin or more prominent warts compared to the smoother skin of the female. These characteristics are not always conclusive and can vary based on the toad’s age, health, and environmental conditions. These general observations serve primarily as preliminary indications rather than definitive proof of sex.
Behavioral Clues: The Significance of Calling
A distinct indicator of sex is the toad’s vocal behavior, particularly during the breeding season. The loud, sustained, and species-specific sounds are known as advertisement calls, and only sexually mature males produce them. The purpose of this vocalization is to attract females to a specific breeding location, such as a temporary pond. Calling is usually temperature and moisture-dependent, typically occurring during warm spring or early summer nights following rainfall.
Observing a toad producing a sustained, melodic trill or croak immediately confirms the individual is male. This advertisement call is distinctly different from the “release call,” which both sexes can produce. The release call is a rapid, short series of clicks or chirps used as a defensive mechanism, often heard when a toad is handled or when a male mistakenly attempts amplexus (the mating embrace) with a non-receptive partner.
The release call signals to the gripping individual that they have the wrong partner, prompting them to release their hold. While hearing a release call does not confirm the sex, hearing the sustained, loud advertisement call unequivocally identifies the caller as male. The absence of an advertisement call, however, does not necessarily mean the toad is female, as a male may simply be non-breeding or silent.
The Definitive Check: Nuptial Pads
The most reliable anatomical feature for determining a toad’s sex is the presence of nuptial pads, found exclusively on sexually mature males. These specialized glandular structures are located on the forelimbs, typically appearing as dark, thickened patches on the inner surface of the first or second digit (the thumb). The pads are often dark brown or black, contrasting sharply with the surrounding skin.
Nuptial pads are composed of keratinized spines or tubercles, giving them a rough, sandpaper-like texture. Their function is to enhance the male’s grip on the female during amplexus. The rough surface allows the male to securely grasp the female’s body, preventing him from slipping off during the aquatic mating ritual.
The development of these specialized pads is regulated by male sex hormones, making them an androgen-dependent secondary sexual characteristic. They are typically only present, or significantly enlarged and darkened, during the breeding season when testosterone levels peak. Outside of this period, the pads may regress, becoming less noticeable or disappearing completely, which can make sex determination in non-breeding males challenging.
To check for nuptial pads, careful and gentle handling is required to inspect the toad’s forelimbs. The presence of these distinct, dark, spiny patches confirms the individual is a sexually capable male. If the patches are absent, the toad is either a female or a male outside of its reproductive season. The definitive nature of the nuptial pad makes it the standard method for sexing toads within a scientific context.