This is the story of a gang of giant toads.
They came to Australia to do a job but they bungled it.
Once they were hailed as heroes now they are big trouble.
How did they get here and what went so wrong?
Meet the accused: an undesirable alien
Name: Bufo marinus, the cane toad.
Origin: south and Central America
Undesirable behavior: a tendency to poison native wildlife.
Status: currently rampaging through Australia's countryside,
a dangerous immigrant determined to be an Australian citizen.
The tropical rainforests of south America.
This lush world is the cane toad's original home.
Here it lives a blameless life
completely in harmony with the environment that provides all its needs.
So how on earth did they end up here,
9,000 miles away in the suburban back gardens of northern Australia
and not just a few either
there are millions of them
ten times the density you'll find in their native habitat.
What brought these immigrants here and who let them in?
The story is rather astonishing.
Queensland, Australia, 1935.
Sugar plantations were in the grip of a devastating plague.
The canes were collapsing and dying in acres
and this was the culprit, a native beetle
that has simply taken a liking to this sweet introduced crop.
The adult beetles chewed the leaves
but the real damage was done by their grubs
which hatched underground and destroyed the roots.
Farmers were desperate.
No traps, no poisons would stop this destructive pest.
But then came news from overseas
where tales were been told of a giant south American toad with a big appetite for beetles.
Some of these toads had already been taken to cane fields in Hawaii
and they'd apparently shown some promise in beetle control there.
Maybe toads were the answer.
The Australian farmers sent a man to Hawaii to collect a few.
102 toads were packed up
and sent on a journey that would take nearly 3 weeks.
Their mission: biological warfare.
When they finally reached Australian soil, they were welcomed with open arms.
Farmers were delighted to find all but one had survived.
These were clearly tough little animals.
Toads were released among the stricken cane and everyone held their breath.
But there was a snag
Unlike those in Hawaii,
the beetles here lived so high up in the cane,
that toads down on the ground simply couldn't reach them.
The whole idea was a flop.
Things got rather worse.
The toads found the cane fields far too dry for their liking
and they soon marched off in search of wetter surroundings
and food they could actually eat.
Australia has no native toads
and now suddenly here were foreign ones running loose.
The consequence of that would be far reaching
Cane toads are accomplished travelers.
In rapidly increasing numbers, they've spread through Australian bush
and made it to the suburbs.
Here they found all their most basic needs provided for.
Like any other amphibian cane toads need water to survive
and in suburbia, there's plenty.
They don't need to drink it
they simply soak it up through their skin.
The bumpy texture, a classic feature of a true toad
channels moisture and keeps it on the skin while it's absorbed.
Dehydration can be a real problem for amphibians,
but cane toads can loose half their body water before it becomes life threatening.
And by huddling in human places during the heat of the day,
they can stay even more agreeably damp.
But it's after dark that these animals really come to life
The back garden is the perfect venue for a spot of romance.
Cane toads need water to breed
and they'll use most kinds of pond natural or manmade.
The males start things off, calling to lure in a local female.
If she finds a call appealing,
a female loaded with eggs will travel quite a distance to reach the water
and the chosen male.
She's made it.
These toads are opportunists.
Where water is available, no matter what time of year,
there will always be a cane toad breeding somewhere.
The male grasps the female with special pads on his thumbs.
Now they are virtually inseparable
as he waits for her to release her eggs and that can take hours.
When she's finally ready they enter the water for spawning.
He wraps his legs around hers
and with a wiggle of his hips
he fertilizes the chains of eggs that tumble from her body.
As she spawns, she swims
festooning the vegetation with jellied strands 20 m long.
There may be 30,000 eggs here
far more than those laid by any native frog.
Once laid, they are abandoned but they are quite safe from harm.
That's because these eggs are poisonous
and will kill almost anything that eats them.
This is where the cane toad's mischief really begins.
In just 36 hours, the eggs become larvae.
The embryos emerge from their jelly wrapping
and the water fills with tadpoles.
In a garden pond, this would seem merely a nuisance,
but cane toads have not confined themselves to the suburbs.
The natural waterways too have been invaded
and here they have really made their presence felt.
Native frogs are facing strong competition.
Cane toads are simply far more successful.
The number of offspring they produce is phenomenal.
Vast shoals of tadpoles tens of thousands of them
cruise through the shallows eating all the available food
and leaving little for anything else.
They eat mainly algae,
but they won't say no to a bit of a dead fish.
More disturbingly,
they seem to have developed a taste for native frog spawn.
In these numbers, such ferocious feeders
could have an impact on the native frog population.
However, a massive young animal is bond to attract predators.
These have caught the eye of a crayfish.
A snap of a claw and that's one less tadpole.
It seems as if danger lurks around every corner
For a fish like barramundi tadpoles should be easy meat.
But there's a twist.
These tadpoles grew from poisonous eggs
and they are even more poisonous now.
One taste is enough.
These fish won't touch them again.
If they swallow one, they'll die.
In fact, only a fraction of Australian animals can eat cane toad tadpoles and survive
And with so little to stop them, their numbers just grow and grow.
In the wilds and in suburbia, the tadpoles get bigger
and begin the next stage in their astonishing transformation.
It takes them just three weeks to grow limbs, absorb their tail and develop lungs.
They are ready for a life on land far quicker than most native frogs.
Suddenly they can breathe air and they can hop.
The next generation is marching forth.
At this stage, life is dangerous for them.
The tiny toads have lost the poison they had as tadpoles
and they quite likely to get eaten.
The first enemies they meet may be their own bigger cousins.
A juvenile toad will happily eat a younger one
as long as it fits in its mouth.
A lucky escape.
As they grow up,
these juvenile toads not only have a tendency to eat their relatives,
they start to become poisonous again
And this time the poison is more powerful.
Glands on their shoulders, carry a toxin strong enough to kill a snake.
It seems that nothing can touch these untouchable toads.
Nothing, that is except this snake.
It's a Keelback and it eats little cane toads.
It's the only Australian snake that's immune to their toxins.
They've met their match.
If the toads survive their youth,
they may eventually grow to more than two kilograms.
That's big.
At this size, they are able to leave water for extended periods.
And in one night a single toad may advance as much as three miles
And there is not much to stop them.
The perils now are mainly from people and they don't make much of an impact.
When you are this big, finding food is a priority.
Garden night lights are a beacon for a cane toad in search of a meal,
Insects drawn to the light are not difficult to catch.
A feeding toad is an intriguing sight.
Having snatched up a morsel with its tongue
it draws it into its mouth and with a colossal blink
uses its eye balls to help push it down its throat.
Cane toads are not fussy feeders.
They have been known to eat small snakes, lizards, even mice.
They seem to have some odd tastes -
dog food seems a particular favorite
Where dog food is put out on the regular basis,
cane toads will gather draw in by the smell.
It appears they also have rather good memories.
They'll even hang around with the dogs waiting for the food to be served.
They seem to relish this ready-prepared feast.
Most frogs and toads need their food to be moving in order to see it,
but not the cane toad.
It simply tucks in.
Domestic dogs and cats can become quite ill and even die
if they mess with these toxic toads.
The toads appear unperturbed.
Such indiscriminate eating habits have made cane toads seriously unpopular with some people.
Australian beekeepers were among the first to complain
when the toads were introduced.
Their hives so carefully tended soon became a magnetic attraction for the new comers.
The toads discovered a taste for bees
and ever on the lookout for new sources of food,
they soon took the opportunity of adding this dish to their menu.
For such an easy meal,
they seem to be quite prepared to put out with being stung
and they gather in groups to gorge themselves.
It's this ability to take advantage of what's on offer
that's made them so successful.
Beekeepers try to retaliate by putting their hives up on blocks out of reach
but the toads soon learnt that if they hang around long enough,
dying bees will eventually drop out.
After that, it's easy... relatively.
But what has really made the cane toad a force to be reckoned with
is its ability to get around.
This creeping Titanian is advancing at a rate of 16 miles a year.
That's a lot of ground to cover.
But some are moving far greater distances than that
and humans unwittingly are helping them.
Cane toads are fond of hiding in damp, dark places
and this has opened up whole new horizons for them.
They become stowaways
and their means of travel have sometimes been surprising.
Comical as it may seem for toads to be hitchhiking
this is actually a rather alarming state of affairs.
In this age of fast transport
cane toads are now popping up all over the place.
They can be taken by mistake to a new area hundreds of miles away
where they may escape and start breeding
The rapid advancement to these poisonous aliens is becoming a serious worry
and they are very hard to stop.
In 70 years they've infiltrated almost a 1/5 the continent
Since they were first brought into the Queensland cane fields in 1935
the toads have spread steadily south towards Sydney
and west into the northern territory.
And they show no signs of stopping.
They are now pushing into some of Australia's most precious natural landscapes
and the outcome won't be favorable.
Australia is an island.
It's split away from the rest of the world 50 million years ago
and so it's full of the most extraordinary animals
that have evolved nowhere else on earth.
This is a quoll. It's a marsupial about size of a cat
and it lives in Australia's northern woodlands.
It's unique to Australia and so it's not used to poisonous foreigners.
However it's a hunter
and it might try to make a meal of something like a toad.
But any quoll that bit a cane toad would make a fatal mistake.
It will get a mouthful of poison.
The glands on the toad's shoulders produce a cocktail of chemicals
which would act quickly on the heart and nerves of its attacker.
The toxins would cause hallucinations
heart failure convulsions and death would soon follow.
If a quoll did eat a cane toad, it will be doomed.
Quolls are already rare
and it seems that numbers of this unique little animal
have badly affected wherever the toads have advanced
to lose it completely would be tragic.
And still the toads push on.
The implications are enormous.
All sorts of native carnivorous animals could suffer from this onslaught
and the toads are about to breach another major frontier.
Kakado National Park far to the north.
It's the jewel in Australia's crown.
This beautiful area contains a variety of wildlife such as exists nowhere else.
Alien toads here could be a disaster
and the horror is they may already be on the outskirts of the park.
There are may animals here that will die if they try to eat one.
Elsewhere even crocodiles have been found dead with cane toads in their mouths
And among those in the front line are the native frogs.
Not only will their waterways be tainted with poison,
they could be overwhelmed by the sheer numbers of invading toads.
No one is sure just how far they've infiltrated the park
or if local frogs have yet suffered
but now a stake out has been set up.
All through the forest, microphones are listening
scientists are waiting anxiously for calls.
The Ornate burrowing frog.
That's ok. That's a native.
The bumpy rocket frog
good to know that's still here.
Bufo marinus.
The cane toad has made it over the boarder.
But the fact is, listening for their arrival is all we can do for now.
No one knows how to get rid of them.
Nothing short of a biological marlfare will do the job.
How strange? That's what they came here to do.
Only time will tell just how big an impact they will have on Australia's wildlife.
But it's hard not to feel a sneaking respect for this sturdy amphibian.
Plucked from its south American home,
it settled into a completely alien environment and is thriving.
They didn't ask to come here.
They were press ganged by humans desperate for their skills.
Now the tables have turned.
Citizen cane toad is no longer welcome to these shores.
Subtitles by Andrew and Hattie www.mvgroup.org