It's not unusual for the odd cane toad to hop a ride on a truck or car and hitchhike down the east coast of New South Wales, but a growing tally of these warty, toxic pests have made their way to a private property an hour's drive north of Sydney – and the threat is being taken seriously by biosecurity experts.
The cane toads were found hiding under a sheet of tin on a private property at Mandalong, a suburb of southern Lake Macquarie in the Hunter region.
The NSW Department of Primary Industries (DPI) biosecurity team admits it is possible the invasive pest has been breeding on the property.
If this proves true, it says the potential for "explosive" numbers to emerge during the summer months is an unwelcome but real prospect.
"We're still getting to grips with how big a problem this is and we won't know that until we have a few weeks of community reporting, to see how far out this population may go," said NSW DPI biosecurity manager Quentin Hart.
The toxin-oozing cane toad is widely acknowledged as a destructive predator that can devastate native animals and ecosystems. They can also poison domestic pets, if swallowed.
A total of 17 cane toads were initially found at the property.
The NSW DPI has confirmed the discovery of another two toads in a subsequent search.
First outbreak since 2010
Mandalong is more than 500 kilometres south of an established cane toad containment zone around the Clarence Valley on the NSW North Coast.
It is understood to be the first significant outbreak of cane toads beyond that buffer zone since 2010 when the amphibians took up residence in Sydney's Taren Point.
The big question is: Did the toads breed on-site or were they unknowingly trucked in as tiny toads, for instance, in garden supplies or some other item brought onto the property?
"We may get lucky, it may be confined to this very local area," Mr Hart said.
"But we won't really know the true situation until we can assess whether cane toads are breeding this summer."
If the toads did breed locally from tadpoles, it seems likely they'll be much harder to eradicate.
Cane toads in Australia
The cane toad is an introduced pest that was brought to Australia in the 1930s as part of a biological control program for beetle pests affecting the sugar cane industry.
They are truly prolific breeders, more so than rabbits, according to conservation scientist John Clulow, a former associate professor attached to the University of Newcastle.
"A decent breeding size female can produce 25,000 to 35,000 eggs in a single season," he said.
"Most of those in a good breeding event would be fertilised and turn into tadpoles in a pond. So you don't need too many.
"If one or two females succeed, then you've got a real problem."
Professor Clulow has been assisting the NSW DPI response since the toads were discovered last week, including testing of tadpoles in a nearby waterway.
So far, only native frogs have been identified.
However, one of the toads in the Mandalong cluster was a fully developed reproductive-aged male.
"The concerning possibility is that they may have been the result of a breeding event down there at Mandalong," Professor Clulow said.
"That's the real concern here and I think that's what's concerning DPI and biosecurity people that we may have quite a problem on our hands."
According to Professor Clulow, numbers can be "explosive" particularly when cane toads move into new areas.
"Once a population moves into a new area it can be really catastrophic for native fauna," he said.
The NSW DPI is encouraging all residents in the area to keep a lookout for cane toads and report any sightings to the DPI Biosecurity Helpline on 1800 680 244.
