The Toads Are Coming, The Toads Are Coming!

The Cane Toad. Click for image source

Invasive species can become quite a problem. One particularly troublesome invasive species in Australia is the cane toad. Fortunately, Professor Rick Shine and his collaborators at the University of Sydney have discovered five effective solutions for reducing invasive cane toad numbers and possibly eliminating them altogether!

Cane Toads in Australia

Cane toad spread from 1940 to 1980. Image: Wikipedia

Cane toads are very poisonous toads native to Central and South America. In 1935 cane toads were brought to Australia from Hawaii in hopes to control insect pests (cane beetles) in the sugar cane. Unfortunately the cane toads had no effect on the insects, but began to spread and grow quickly.

These nasty toads are very toxic and cause a lot of problems for Australia’s native species. Poor, unsuspecting native predators are not familiar with the toad and so their new meal ends in fatal poisoning. There has been a serious decline in many toad predators such as snakes, lizards and even crocodiles.

Australia has spent millions of dollars on trying to remove cane toads, but all attempts have failed. Some early approaches were to offer rewards for shooting or trapping toads. There was even an advertisement to play golf with them! This caused all kinds of problems because it’s not always easy for a person to differentiate between native frogs and the invasive toads. In the end, the toads have prevailed by increasing their numbers faster than we have been able to eliminate them. 

Cane Toad ad. Click for source

Shine Lab Research

Professor Rick Shine and cane toad. Click for source

Shine’s research group called “Team Bufo” has investigated this invasive species in depth. They have found that to solve a problem you need to understand it well. Their research to understand the cane toads has revealed five solutions to get rid of them.

1. Minimize breeding-site options

It turns out toads are very particular about where they choose to breed. They prefer shallow pools with lots of open edges. By planting dense vegetation around edges of these pools the cane toads will avoid them and we can actually control where they breed.

2. Infect them with parasites

Lungworms are parasites that actually came with the toad, and Team Bufo found that this species doesn’t actually affect native frogs at all. This parasite infects the lungs of the cane toads making it more difficult for them to breath and then greatly affecting their locomotor abilities. The cane toads at the invasion front are too fast and don’t get infected with the parasite, so if the lungworm is moved to the toad invasion front it can hopefully infect the majority of the group. Additionally the large toads are cannibalistic and are the most likely to survive. By infecting little toads in concentrated breeding locations we can increase the parasite spread.

3. Competition 

Native frogs actually breed earlier in the season and so their tadpoles are larger. The cane toads will avoid ponds with lots of frog tadpoles. When toad and frog tadpoles are together, the toad tadpoles are complete wimps. This tadpole competition reduces the toad tadpole survival and growth.

4. Native Predators

Meat ants devouring cane toadlet. Photo: Georgia Ward-Fear

Although many predators have found their death due to the cane toads, there are some Australian birds, rodents and insects that are not as affected by the poison. Carnivorous ants, in particular, may be quite helpful in controlling toad numbers. These ants are not affected by the toxin, but the toad will just sit still and be carried off by the ants expecting the toxin to have its effect. If we use cat food around water bodies with cane toads it will attract the ants and thereby help reduce toad numbers. Also, there are useful aquatic insects that eat toad eggs and tadpoles which we can help influence.

5. Toad tadpole chemicals

Smaller baby toadlets following exposure to the alarm pheromone. Click for source

A toad’s greatest competition is actually with other toads. Team Bufo’s research has found that tadpole chemicals may be the best method to reduce toad numbers and possibly eradicate them. The tadpoles have alarm, attractant and suppression pheromones that do not have any effect on native tadpoles. The alarm pheromone will actually hinder tadpole development and reduce their survival and size. Attractant pheromones lure cane toad cannibal tadpoles. Shine’s lab found that by using this chemical in a funnel-baited trap that can catch thousands of tadpoles. It is extremely effective and there are already community groups using this trapping method. Lastly, exposing toad eggs to tadpole chemicals was found to suppress the development of younger tadpoles. Apparently older and younger tadpoles were not meant to mix.

Conclusion

By using these five methods in combination with each other we will be able to restrict toad breeding sites, suppress their movement and development, and be able to possibly eliminate them completely. Shine has clearly demonstrated that you can find solutions to a problem by understanding it well.

Further Reading

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