Increasingly a problem in Australia, packed with poison and highly adaptable, the invasive Cane Toad, has failed to be stopped advancing its frontiers!
Experts are now on alert after Cane Toads have now been found close to Sydney. They have evolved to be faster, bigger, and stronger than those introduced into Queensland to control the Sugar-Cane Beetle. Failing to be effective as biocontrol, they now are capable of colonising at least four mainland Australian states and are proving to be more-or-less indestructible!
1. What is a Cane Toad?
Ranked 16th on the World’s 100 Worst Invasive Species list the Cane Toad can weigh up to 2kg.The Cane Toad, also called the Bufo, Giant Toad or Marine Toad, is a large, heavily built, amphibian. Adult Cane Toads are generally 9-15cm long but can grow up to 24cm. Their skin is rough, dry, and covered in warts. An awning extends over each eye and an angular shaped bony ridge extends from eyes to nose. Their colour can vary from red/brown to grey/brown.
The Cane Toad’s the parotoid glands are located just behind the head on either side behind the ear. The parotid gland is loaded secretions which are extremely toxic and lethal. These deadly cardiac toxins provide protection by keeping predators away from the toad. When eaten by larger predators like goannas, snakes, or freshwater crocodiles the poisons are potentially fatal.
The toads devour insects and other small prey. They hunt at night especially on warm, wet nights. During the day they hide under rocks, fallen trees or any shaded, cool cover they can find. They lose huge amounts of essential body moisture to evaporation during the dry season. Yet can survive a loss of up to 50% of their body water in temperatures from 5-40°C.
2. Why are Cane Toads a problem?
Cane Toads are an invasive species with no natural predators in Australia. They will eat almost anything and reproduce quickly, and they are toxic at all stages of life. The poison they exude can kill many native predators whose populations have since declined.
Toads have been linked to the decline and extinction of several native predator species including the northern Quoll in the Northern Territory and the rainbow bee-eater birds in Southeast Queensland declining by 33% due to Cane Toad predation. A total of 75 species lizards, crocodiles and freshwater turtles are threatened with 16 classified as ‘threatened species’
The environmental damage they cause includes poisoning and killing anything that that eats them including from birds, mammals, and reptiles. They eat small reptiles, insects, and other amphibians.
The warty amphibians move only during the wet season. Cane Toads are now present in their millions and are expanding from Queensland into New South Wales
The Cane Toad’s success at surviving and thriving in Australia is remarkable considering they are amphibians which are poorly adapted to most of the country’s climate. They were first declared a problem in 1950.
3. Why did Australia introduce Cane Toads?
Australia did not have any toad species of their own to kill crop pests. Cane Toads where originally imported from Hawaii and released in Queensland in the 1930’s as a biological control for the beetle pests of sugar cane crops.
The main problem was the Greyback Cane Beetle and the French’s Cane Beetle that were decimating the north-eastern state of Queensland’s sugar cane crops. The beetle’s larvae were eating the roots of the sugar cane which led to either stunted growth or killing the plants.
While the Cane Toads thrived in the wild, they had no noticeable impact on cane beetles which are today controlled by pesticides. The scientists who brought Cane Toads to Australia did not think through the possible impacts on native wildlife and did not consider the possibility of toad-induced mortality of native predators.
4. Did the introduction of Cane Toads fail?
The introduction of the Cane Toad was surrounded by controversy as to the cost verses benefits to Australia.
Around 1935 as the Cane Toad was introduced it was hoped it would control the pests of economic importance to the sugarcane industry, these being the Greyback Beetles and French’s Cane Beetle. However, by 1941 it was apparent that the Cane Toad was having only limited control over the targeted prey.
Main reasons for the failure were
- Greyback beetles invade cane fields when the toads are absent due to there being insufficient protective cover in the early stages of the sugar cane growth.
- Grey back Beetles exist higher up on the sugar cane than the ground dwelling Cane Toad can jump and only occasionally are in contact with the ground.
- The Cane Toad’s diet is wide ranging and not solely reliant upon its intended prey.
The unlimited variety of other insects and prey the Cane Toad, along with the suitable environment and few natural predators allowed rapid reproduction and spread.
In only 10 years after their release, Cane Toads were recorded in Brisbane. The toad has continued to thrive and has now invaded New South Wales and Northern Territory. Those at the frontline are even larger than those in established populations which is possibly due to the greater food supply and lower incidences of disease.
5. How many Cane Toads are there in Australia today?
In less than 87 years the Cane Toad population has multiplied to epidemic proportions, with more than 200 million Cane Toads in Australia.
Cane toads have increased their range by about 10km a year since the 1940’s. They are now invading new areas at an accelerated rate migrating and expanding at an average of 60 kilometres per year. This has been measured by researchers attaching radio transmitters to the toads which found that the toads with longer legs move faster and are the first to arrive in new areas. The longer legged toads have more endurance travelling approximately 0.5 kilometres further in a three-day period.
They are moving so fast due to the pressures that flow from an invasion as every generation at the invasion front are the ones that have gone the farthest, they are the faster moving toads. The research demonstrated that these changes in a toad’s body shape, its behaviour, dispersal capabilities and tactics are heritable.
Their hardy nature and voracious appetite have led them to become prolific invaders, wreaking havoc on Australia’s ecosystem.
6. How are scientists trying to stop Cane Toads spreading?
In 2021 three viruses in the Cane Toad’s DNA were discovered, which could be converted into a bioweapon to control the population or wipe the species out!
As with any virus development in the laboratory, these viruses would have to be field tested before full scale release to ensure there are no impacts to other native animals, so turning the table on these pests will take time.
Previous methods of controlling Cane Toad numbers have included mesh fencing and traps, but native fauna can also get caught up in the nets. Physically removing them from the environment is an immense task so it has also been easier to collect jelly like chains of cane toad eggs from local ponds and creeks.
Other previous scientific studies to control the Cane Toad spread have been to use parasites and toad communication. The alarm pheromones are released into a pond or creek when a tadpole is injured or frightened and warns other toad tadpoles to flee the area. Those that then became adults were half their normal size or die before reaching adult toads before
The lungworm parasite has together with the alarm pheromone can either kill or produce smaller baby toads and the parasite is successful in killing the smaller sized toads.
The Australian government has spent over $20 million on attempts to control Cane Toads and so far, nothing has eliminated them!
7. How can you get rid of Cane Toads in the yard?
To make your home Cane Toad free you must
- Always cover or bring pet food in at night
- Remove rubbish such as wood piles, pots, and metal sheeting, where it’s safe to do so Cane Toads cannot shelter under it during the day
- Discard any standing water and reduce any water around the house
- Turn outside lights off, outside lights attract insects and toads eat insects
- Keep toads out by using fencing which is well maintained. Native doors can be a gutter guard or similar mesh that allows native animals to get in and out of the barrier
8. What to do if you see a Cane Toad?
Any sightings must be reported to the DPIE Biosecurity Hotline 1800 680 244, or report it online by going to invasive.species@dpi.nsw.gov.au. To confirm that the toad is a Cane Toad a photo may be sent.
The animals are covered by animal welfare laws so if you need to kill the toad it must be done humanely by stunning followed by decapitation. If there are large numbers, it is recommended for an experienced and skilled person to be used. It is also acceptable to Spray the toad with Hopstop®
A most common way which is considered humane to put the toads in a plastic bag and freeze them. First the plastic bag or container must be placed in a fridge at 4°C for 12 hours so that it becomes unconscious. Once in the freezer (-20°C) to kill the toad painlessly. They must be left for a couple of days especially if there are a good number of toads in the bag, as it takes a while for it to freeze them to the point where it kills them.
9. How do you safely collect Cane Toads?
To ‘Toad bust’ your yard this involves regularly checking your property for toads and if sighted and identified they must be caught!
The problem that they can secrete and possible squirt a toxin when the toad is roughly handled or feels threatened. This venom causes severe symptoms and even death in people if swallowed or absorbed through the mucous membranes such as the eye, nose, or mouth. Cane Toads are toxic even after they are dead!
Before collecting the Cane toad take pets away from the area and make sure children are properly supervised, then
- Wear eye protection or safety glasses
- Wear protective gloves which can either be gardening or rubber gloves
- If using a plastic bag, they must be doubled up by placing one bag inside the other and then turned inside out. The toad can then be grabbed by the back legs, then turn the bags the right way and tied at the top
- Hands must be washed thoroughly with soap afterwards.
- Gloves or any other items which have the toad may have touched must have an antiseptic wash
Some areas in Australia have drop off points where they will be identified and humanely euthanised.
Once left in the freezer for at least 16 hours the dead toads can be buried or put in the compost as a safe fertilizer if the compost is away from pets.
10. What happens if a Cane Toad is touched or licked by a human?
Cane toads are not aggressive creatures yet when threatened will excrete a milky white toxin from their parotoid glands which can be both an irritant or potentially fatal if it gets into the eyes or mouth. At the very least it can cause pain and severe irritation to the eyes and short-term visual disturbances. Mild symptoms include gastrointestinal signs such as nausea, vomiting and abdominal discomfort.
A specific antidote for these toxins is not available and treatment concentrates at minimizing toxin absorption and controlling clinical signs. For eye irritation first aid treatment includes washing the eyes, mouth, and nose with lots of water, then seeking medical attention.
Even though the milky poison Cane Toads secrete can kill you this poison called bufotoxin contains several different chemicals one of which is a hallucinogen called bufotenine. The strange habit of licking the Cane Toad can be very and make you intensely hallucinate and possibly die. The compounds secreted are meant to incapacitate and kill predators!
Some dogs have been reported to become addicted to the hallucinogenic sweat that oozes off the backs of Cane Toads. Dogs become so desperate to get their fix that they deliberately hunt down these amphibians to stimulate their deadly poison then lick their prey!