July 2019

Dangerous dining

 I came across this snake wrapped around a toad. Can it really eat that thing, and will it be harmed?

Answer

Pythons are constrictors which prey on a wide variety of vertebrates, particularly mammals, birds and reptiles. They do not usually eat amphibians but there are plenty of documented cases of carpet snakes dying from attempted predation on cane toads. Photo courtesy of Errol Koch.

This picture may look humorous, with the little Carpet Snake appearing slightly silly draped around a big fat toad. But it illustrates a scenario that has been unfolding in Australia for decades with disastrous ecological consequences.

Pythons are constricting snakes that eat a wide range of vertebrates, particularly mammals, birds and reptiles. Like all snakes, they can locate prey following chemical cues. The forked tongue picks up organic particles and transfers them to an organ in the roof of the mouth called Jacobsen’s organ where they are identified. Most species of pythons, including Carpet Snakes, also detect warm-blooded prey using heat sensory pits in scales on the snout and along the lower jaw.

To deter predators, Cane Toads are armed with powerful poison located in the skin, and particularly in the large parotid glands on the neck. When harassed the poison oozes from these glands in the form of a thick white fluid. Toad poison is so toxic to most predators that even holding one in the mouth is likely to have fatal consequences. There are plenty of cases where predators are found dead with a toad, un-swallowed, still held in the jaws.

Having been introduced into a continent previously toad-free, they have dispersed widely and rapidly, unchallenged by any significant predators. In the wake of their expanding range, populations of goannas, quolls and many snakes, have crashed.

Pythons do not usually eat amphibians but this Carpet Snake has found a toad. It was almost certainly located by chemoreception, because toads are ectothermic creatures that do not radiate body heat. Pythons can disengage their jaws and consume significantly large prey items, but this big toad is probably outside the snake’s league. It is highly unlikely the little python could swallow a toad that size.

However the carpet snake is dicing with death. Any contact between its moist mouth lining and the toad’s skin, will probably be lethal. If it attempts to swallow the toad, or even opens its mouth to try the toad out for size, the snake could die.

We hope this had a happy outcome, as snakes do sometimes abandon a meal. But toads remain as an ever growing threat to Australian fauna.

Queensland Museum's Find out about... is proudly supported by the Thyne Reid Foundation and the Tim Fairfax Family Foundation.

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