The Most-Traveled Cane Toad

Lookin' like a cane toad... mug shot identification.

Questions answered (and bookmarked) on this page:

Describe the appearance of a cane toad. 

How can I identify cane toads from other toads in my area? 

Are males and females identical?

The mug shot:  First, consider the appearance of a cane toad.  Cane toad eggs are black.  Cane toad tadpoles are completely black and between 1 and 2.5 cm in length, with tail length equal to the body length. 

New metamorphs are about 1 cm in size and lack large parotid glands.  They have relatively narrow bodies, broad heads with blunt-snouts and lateral nostrils, and tend to be slightly   greenish--but vary in color.  Both metamorphs and adults have unwebbed fingers (front feet), moderately webbed toes and callouses (on back feet), light colored bellies, horizontal pupils, and have many warts on their backs.  Warts on the legs are smaller than warts on the back, and in males, each wart has at least one spike protruding from it. 

There is a large ridge above the eye and often a less prominent, more incomplete ridge below the eye.  The ridge under the eye runs to the tip of the eye and then along the side of the flat portion of the skull towards the snout, where it merges with the ridge from the other eye; the ridge then runs down the center of the snout, between the nostrils.  Collectively this ridge design appears like an “M” shape.  Behind and slightly below the eye is the tympanic membrane (external appearance of the internal ear), which presents as being slightly large than half the size of the eye and light in color.  Adults tend to lose the greenish tinge, instead being shades along the continuum of red, brown, and black.  The parotid gland will be very prominent, and the angle and position of the parotid gland helps to distinguish it from other species.  After 5 cm, cane toad adults have a 4:3 length to width ratio.  For example, a toad might be roughly 6 inches long by 4.5 inches wide.  Their bodies are relatively flat.

   Yep, pretty flat!

Differentiating a cane toad from other anurans can be (sometimes!) fairly easy but depends upon where the cane toad is located.  It is confused with different species depending upon whether the toad is in Australia, South America, or any other location.  Generally these toads sit rather erectly and are terrestrial (one pair has been observed 2.5 m up in a tree!). 

In Australia, the cane toad is the only “true toad” on the continent.  It is distinguished from other species by its sheer adult size and the presence of the distinctive parotid glands.  In the United States, the cane toad is sometimes confused with Bufo terrestris, which has knobs on top of its head and has a kidney-bean shaped parotid gland, whereas the parotid gland of the cane toad is angled over the shoulder.  In South America, distinguishing the cane toad from related species can be more difficult, in some cases requiring DNA analysis.  An identification key for related South American species is provided in a research paper .  See Axel et. al in the references page for the citation on this key. 

Always lookin' sexy, adult cane toads have been most flatteringly described as “looking like mobile cow patties”, as they often have widths that are 75% their length.  (Do remember the picture up the page...the toad does kinda looks like a cow patty.)  Hence a large toad may be 9 in (23 cm) long by 7 in (18 cm) wide and weight 2.2 pounds (1 kg).  In areas of high toad density, toads attain smaller adult sizes than they would in less populated areas.  Females are larger than males.  Females tend to have backs that are more mottled and darker in coloration, exhibit a light colored stripe down the spine, and be less bumpy than males.  The warts of females tend to be larger and less uniformly distributed along then back.  During breeding season, the male tends to exhibit the keratinized thumb patch known as a nuptial pad.  However helpful the above characteristics may be in suggesting the gender of the toad, none definitely identify a male from a female.  Indeed, short of dissection, the best way to identify a male from a female is by observing two vocal sac openings on the mouth floor, under the tongue. 

 

Above: On the left are males; note the lack of strip down the back.                     The female is pictured on the right (due to copyrights, I cannot make the picture larger-sorry!).

 

 

Hmm.  Well, if you can sorta identify these toads, you're almost done with what I have to offer.  Try Toad'ly habits if you want amusing facts.  If you're hardcore on toad history and want to know some evolution, try Tree of Life.