Cane toads cannibalise their young

Scientists say that harnessing cane toads' cannibalistic behaviour may be the key to getting these pests to eat themselves out of existence

Cane toads wiggle their toes to lure their young, then eat them up in an act of cannibalism, Australian researchers say.

They say the young toads move towards the adults, possibly mistaking the wiggling toes for a tasty morsel, like an insect.
Instead the youngsters themselves end up as the tasty morsel.

But harnessing this cannibalistic behaviour may have some benefits, at least in Australia, where cane toads are an invasive pest.
Scientists say it could be the key to getting cane toads to eat themselves out of existence.

Professor Rick Shine of the University of Sydney and PhD student Mattias Hagman will report their findings in the journal Animal Behaviour.

The researchers noticed that when baby toads are around adult toads, the adults start wiggling the middle toes on their hind feet.

The baby toads appear to respond by hopping towards the adults.

The researchers wondered whether this toe waving is an adaptation for cannibalistic behaviour and set up an experiment to check.

Toads were separated by clear glass and not allowed to eat each other because it would have gone against the rules of ethical animal experimentation.

The researchers found that baby toads only move towards adults that wave their toes.

"[The toe waving] seems to be beautifully designed to arouse the feeding responses of a small cane toad," says Shine. "They presumably think it looks like a small insect."

The researchers also used freeze-dried toad to which they attached mechanically controlled fake toes.
They measured how far the baby toads moved towards the artificial toe as they wiggled it at different rates and changed its colour.

"We showed that the way that the real toads do it is in fact the best possible colour and speed ... to lure baby toads in," says Shine.
He says the findings strongly support the idea that cannibalism is an important enough behaviour among toads for it to have led to the evolution of the special toe-luring trick.

Shine says confirming that toads have evolved to be cannibalistic could be useful in trying to control them.
Shine says males are most likely to cannibalise their young because they congregate around the ponds where females come to lay their eggs.

But females tend to spend more time roaming around the countryside looking for food. This means they are harder to find but present a greater risk to native predators.
While males are easier to find than females, Shine says it could be helpful to keep them alive and focus on knocking off the harder-to-find females.

"We might end up with a group of toads that were very good at eating smaller toads," he says.
Shine also says outnumbering female toads with males would increase the number of female toads drowned by numerous males trying to copulate with them in the water.

He says this selective culling could be combined with a parasite, from native frogs, that has recently been found to kill or stunt the growth of cane toads.
"At the moment it's an idea and we need to run a bunch of trials trying to see how effective that's going to be because at the moment we don't know," says Shine.