In the 1930s, Australian farmers had a really big problem.
Their sugar cane crops were being decimated by a voracious grub, the larvae of the cane
beetle, which destroys the plant’s roots.
After failed attempts at chemically controlling the grubs, officials sought a biological solution.
They thought that if they introduced a predator of the beetle, the grub problem would go away.
At the time the thought process wasn’t entirely unreasonable.
But it would turn out to be the single worst decision they could have made.
After hearing about a measure to control a similar cane beetle in Hawaii with the voracious
cane toad, Australian officials jumped at the idea.
After dutifully carrying out exactly zero studies of the potential impact on the Australian
environment, they transported 100 toads from Hawaii and let ‘em loose.
And with that one single action, the Australian ecosystem was never the same.
100 toads quickly became 1000, and then 10,000, then 10 million, and then 100 million.
They have rapidly spread over much of the continent.
Today, cane toads, properly known as bufo marinus, or bufo toads, are the most notorious
of all invasive species in Australia.
This lumpy guy is massive, poisonous, and seemingly unstoppable.
The biggest cane toad ever recorded was almost 40 cm, or 15 inches long and weighed six pounds,
or 2.75kg.
It eats anything it can fit into its mouth - insects, trash, dogfood, small reptiles,
small rodents, and even birds.
The one thing it doesn’t eat though, is the cane beetle.
Cane beetles perch too high off the ground for the cane toads to reach, and the toads
certainly can’t get to the grubs underground.
So you could say there are some regrets.
Cane toads are now moving westward at a remarkably fast pace, and the Australian government admits
that it's unlikely they will ever be fully contained.
Since their introduction 87 years ago, cane toads have been linked to the decline of several
native species in the Northern Territory and Queensland, including the Australian monitor
lizard, the northern blue-tongued lizard, the Australian water dragon, the king brown
snake, the common death adder, and the northern quoll.
Many species are at risk of total extinction, all because of this stupid, ugly toad.
What is it about the cane toad’s particular biology that makes it so destructive and able
to spread so easily?
Why are some introduced species worse than others, and what can be done to stop them?
Invasive species, unfortunately, have become a major part of our modern world.
They can be introduced to an area by ship ballast water, accidental release, or, like
in the case of the cane toad, by misguided intentional human action.
But a common misconception is that any species found living in its non-native habitat is
an invasive species.
This however, is not the case.
Many species are introduced to new areas without it being a problem.
Most crops are non-native - potatoes, for example, are from south america but are now
grown on most continents without causing an issue.
Honeybees were introduced to the Americas from Europe in the 1600s, and have yet to
cause any major problem.
A species only gets the “invasive” title when it causes harm to the environment, displaces
or outcompetes native species, hurts the economy of the area, or becomes a danger to human,
animal, or plant health.
The brown tree snake has eaten a dozen kinds of forest birds in Guam to extinction; zebra
mussels clog pipes around the Great Lakes and, speaking from personal experience, shred
your feet to a pulp in Lake Travis; house cats murder any creature they can get their
paws on if they are let outside, pushing as many as 70 bird, reptile, and small mammal
species out of existence already.
The kudzu plant is a climbing vine that smothers and outcompetes native plants all over the
southeastern United States, and grows up to a foot a day.
All of these organisms have found a place to thrive where they didn’t originally evolve,
meaning other organisms haven’t had the time to adapt to their presence.
Native organisms don’t have defenses against the invaders, methods to compete alongside
them, or even ways to prey on them.
And the cane toad’s particular biology makes it so most of the natural inhabitants of the
Australian ecosystem don’t stand a chance.
Largely, because cane toads are extremely poisonous.
Adult cane Toads have venom-secreting poison glands on each shoulder where a highly toxic,
milky substance is released when they are threatened.
If an animal tries to bite at the toad, the venom is secreted directly into the animal’s
mouth, and its effect is almost instant.
The venom, which is full of cardiac glycosides, causes sodium to build up within the animal’s
cells.
When this happens in heart cells, it completely alters the rhythm of the heart, usually making
it beat out of control.
Meanwhile, potassium builds up between the cells, which can cause paralysis.
This then leads to difficulty breathing, convulsions, and soon after, death.
A cane toad’s poison can kill within minutes.
This makes the cane toad quite an undesirable snack for most animals, especially animals
in Australia.
In the cane toad’s natural habitat of South and Central America, some predators, like
the broad-snouted caiman, have evolved mechanisms to block the action of the poison.
But similar predators in Australia have not had time to keep up their end of the evolutionary
arms race.
Freshwater crocodiles in Australia are experiencing mass die-offs due to the very same toad.
A study conducted in 2008 saw 77% of freshwater crocodiles die in a period of 3 years, directly
following the inland progression of cane toads from the mouth of the Victoria River.
The pace of their deaths exactly matched the pace of the toads’ invasion.
But all hope is not lost for the crocodiles.
Eventually, the high death rate may naturally select for crocodiles that have a higher tolerance
to the toad toxin.
This is already being observed in some blacksnake populations that have been hit hard by the
cane toads.
And other animals are adapting in even freakier ways.
Australian water rats have learned to flip cane toads over to carve out and eat their
hearts with surgical precision, avoiding any toxins.
The rats even opt for the biggest, most poisonous toads.
It’s easier to avoid the poisonous parts of bigger toads, and if the poison is no bother
to them, they might as well go for the biggest meal.
In turn, this could have a positive effect for other native animals, because the largest
toads getting killed are the more toxic and more dangerous ones.
With enough time, maybe there is hope that Australian animals can fight back.
But, unfortunately, it's not just the adult cane toads that are the problem.
Even the eggs and tadpoles are poisonous, which, if ingested by vertebrate predators
like fish and turtles, can be fatal.
And this is no small threat.
Cane toads don’t just lay a few eggs, they lay an apocalyptic amount of eggs.
And their toxicity, added to their sheer numbers, is creating a completely unexpected evolutionary
event
The life of a cane toad begins within an egg - part of a long gelatinous string that the
female lays underwater and the male simultaneously fertilizes.
One cane toad female can lay up to 40,000 at a time.
This is a LOT of eggs.
But usually when an animal has so many offspring, they don’t expect many of them to survive.
Different kinds of animals have different strategies for their offspring, often described
as the r and K strategies.
K-strategists, like humans, whales, elephants, or bald eagles - have few young and invest
a lot of time and energy into rearing those young, with the idea that all or most will
survive into adulthood.
r-strategists, on the other hand, like mice, octopus, or you guessed it, toads have many,
many young and invest little energy into them, thinking the majority won’t survive to adulthood.
But the problem with cane toads in Australia is that basically all of them do survive.
These tiny black dots speckled down the string of eggs soon will hatch into tadpoles.
And the pond in which they live will become full to the brim, completely blackened with
them, killing most predators that try to eat them.
These tadpoles gradually develop forelimbs and hind limbs, reabsorb their tail, while
their gills disappear and their lungs develop.
Once metamorphosis is complete, armies emerge onto land as young toads.
And these armies are only getting more formidable.
Between the 1940s and 1960s, cane toads expanded their range by about 10km a year.
But today, cane toads are moving west and south at a rate of over 50km a year.
Why are they so much faster now than before?
At first, researchers thought that the toads might somehow be slipping onto to trucks and
hitchhiking across the country.
To find out for sure, they strapped tiny radiotransmitters to the toads.
And what they found shocked them.
The toads were not hitchhiking, but were themselves traveling at an alarming rate - up to 1.8
kilometers a night - far further than any other frog or toad ever studied.
Could this ever accelarating takeover be a result of the army of toads evolving into
a faster toad right in front of our eyes?
While researchers can’t go back in time to race modern toads with the first toads
brought over from Hawaii, what they can do is look at preserved specimens of toads from
decades ago.
And what they found is that over a 60 year period, Australian cane toads’ legs have
grown over 25%.
And scientists soon realized that the modern cane toads with the largest legs are those
on the western front - the first toads to arrive in a new area.
Later waves of toads had much shorter legs.
The cane toads able to spread farther and faster have less competition, and thus there
is an adaptive advantage in doing so.
The cane toads were always spreading fast, but now they are evolving to spread even faster.
This is all pretty worrying.
Where we used to think vertebrates can’t really evolve on such short time scales, the
cane toad is proving that they absolutely can, if the conditions are right.
And for invading organisms, whose populations explode very quickly, this rapid evolution
is all the more likely, and all the more dangerous.
But the intense competition between the toads that’s driving adaptation has an upside.
The toads are quickly evolving a taste for.. themselves.
They have become so numerous that their only natural predator is other cane toads.
And while scientists have observed cannibalism evolving in animals before, they have never
seen it evolve so quickly.
Adult cane toads can be seen eating smaller toads, but its their tadpoles that are doing
most of the cannibalizing.
Researchers found that a handful of more developed tadpoles can devour 99% of the tiny hatchlings
that emerge from the tens of thousands of eggs in a single clutch.
And when compared to the native cane toads of south america, invasive Australian cane
toad tadpoles were 2.6 times more likely to engage in this behavior.
So in this instance, their immense numbers and rapid evolution is helping to put a cap
on their numbers.
But short of the cane toads eating each other out of existence, is there anything we can
do to stop them?
Australians understandably want the cane toads gone, but unfortunately, there’s no great
way to round them up and kill them.
The government, community groups, and frustrated individuals do their best to cull them but
its not easy, and not always humane.
The current guidelines on the ‘most humane’ way to kill cane toads is to stick them in
the freezer.
Some groups try to trap large numbers of toads using speakers to play the cane toad’s song
to lure toads to it.
Other people just straight up shoot them with air rifles, hit them with golf clubs, or run
them over in their cars.
There are even “toad-busting” militias that make it their mission to kill as many
of the toads as possible.
But there are too many toads in Australia to eradicate by simply removing individuals.
That’s why some want to take a more intentional approach.
Researchers are trying to genetically develop a cane toad that can only produce male offspring,
using something called a W-shredder gene drive.
The ZW sex-determination system is a chromosomal system that determines the sex of offspring
of many animals like birds, some fish, some reptiles, and the cane toad.
ZW chromosomes will give you a female, and ZZ will give you a male.
This is sort of the opposite of the mammal system, where the heterozygous XY gives you
a male, and homozygous XX a female.
And in the ZW system, it is the egg that determines the sex of the offspring, unlike in the XY
system, where it is the sperm.
A W-shredder toad is a toad who has been gene edited so that all of its W bearing eggs are
defective.
That leaves just Z bearing eggs.
So when the male adds his Z chromosome to that, you get only ZZ offspring, meaning you
get only male offspring.
And if the W shredding gene is located on the Z chromosome, then this shredding gene
can be inherited.
With enough gene shredder toads in the environment, the numbers of females will be greatly reduced.
And a male-dominated population would be incapable of effective procreation.
Some may argue against this technology - saying we have clearly already messed with nature
enough.
But at this point, when the damage has already been done and the toads march on, we don’t
have the luxury to not intervene.
We as a species already are playing god, whether we like it or not.
So we might as well get good at it.
We might as well do it in a well researched, calculated way to undo some of the damage
we have done.
Despite their destruction, we can be grateful for the cane toads for one single reason.
They are the subject of the single greatest cinematic experience a person could ever have.
This whole video was inspired by a memory cemented in my brain from 10th grade biology,
of watching the most hilarious documentary I have ever seen.
Perhaps you too, have a distant memory of a cane toad named Dairy Queen,-- he’s dancing
line — inexplicable camera angles, amazing interviews – hit them with stick line–
– scientist making sound effects– grown men singing songs in the shower about cane
toads while they stalk him, psycho style?
… All textured with 80s synth and incredible jingles.
It feels like a mockumentary, but its all real - like a lovechild of National Geographic
and Monty Python.
The cane toad problem is obviously an awful thing, but sometimes in the face of a terrible
situation, all you can do is laugh.
And in all seriousness, its a powerful piece of science communication.
This film has been cemented in my brain for 15 years afterall.
As I was trying to reminisce on this magical film, I wondered if I would even be able to
track it down..
And to my great surprise and delight, I realized its on CuriosityStream in its entirety.
I almost could not believe my luck.
If you haven’t seen it, go watch it now.
You will not regret it.
And if you’re like me, and watched it years ago, go rewatch it.
I promise it is just as funny now as it was back then.
And make sure to watch it on CuriosityStream, to support this channel and other independent
creators like me.
CuriosityStream is a great platform in itself with incredible documentaries, but also supports
us to keep making videos like this for you.
And because CuriosityStream has partnered with us, you can get in on an incredible deal.
By signing up to CuriosityStream you now also get a subscription to Nebula.
Nebula is a streaming platform made by me and several other educational YouTube content
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It's a place where we can upload our videos ad free, and a place where we can experiment
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By signing up to the bundle deal, you will get access to both CuriosityStream and Nebula
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There are so many original, exclusive documentaries on Nebula from some of YouTube’s very best
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And if you are looking for something else to watch right now, you can watch our previous
video, the Insane Biology of Venus Flytraps,, or watch Real Engineering’s latest video
The Truth About Carbon Taxes, which in Brians words, discusses future scenarios of how to
‘yeet coal from the electric grid.’