New weapon against cane toads

Cane toad poison is toxic to most animals. Image: mcquilkin/Shutterstock

A dose of their own poison could control these pests.

The deadly poison that cane toads (Bufo marinus) use against native species can now be turned against them. It doesn’t kill them, but it makes an effective bait for toad tadpoles.

Researchers from The University of Sydney (USYD) and The University of Queensland realised the poison’s potential while studying the ecological impacts of the toads. They found that when a female cane toad laid her eggs, thousands of cannibalistic tadpoles appeared.

“A cane toad tadpole’s worst enemy is another cane toad tadpole — they compete strongly for food,” says USYD researcher Rick Shine, lead author of the study published in Proceedings of the Royal Society B. “So if a female toad lays 30,000 eggs in your pond, the best thing you can do is find those eggs and destroy them before they hatch into competing tadpoles.”

The appearance of the cannibalistic tadpoles suggested that there was a chemical attractant in the eggs, so the researchers tested tadpole responses to the various chemicals they were able to isolate. When they tested the poison, Shine says they hit paydirt.

“The poison is a really distinctive chemical — no other frogs produce anything like it — so the toad tadpoles use that chemical to identify and zero in on newly-laid toad eggs.”

The poison can also be found in the shoulder (parotoid) glands of the adult toads, so a trained individual can take a dead toad and squeeze its glands to produce a bait. The bait is then placed in a funnel trap to attract the toad tadpoles within the pond.

The method appears to be successful — Shine estimates that they removed 40,000 tadpoles from one natural pond in less than a week and there haven’t been any toads emerging from that pond since. Native frogs, fishes and insects are all repelled by the bait, so they will not be attracted to the taps.

However, there are risks for humans when it comes to obtaining the poison — it needs to be done the right way and it is essential to wear gloves and eye protection, with no exposed skin. “We are planning to teach people from toad-busting community-groups the right way to do this,” Shine says.

The researchers are also working on developing a stronger and safer bait by isolating the active secretion from the glands. It could then potentially be used in pure forms without the poisons. Until then, a dead toad in a funnel trap will attract the tadpoles, without the risky squeezing.

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