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O
ne winter’s day in 1935, the Australian Bureau
of Sugar Experiment Stations released 3000 cane
toads in north Queensland. The idea was that
the toads (bred from an initial batch of 100 imported
from Hawaii) would control the cane beetles that were
destroying sugarcane crops, reducing the need for
dangerous pesticide use. What could possibly go wrong?
Today, cane toads can be found all the way down the
east coast of Australia, as far as northern New South
Wales. They have spread across the Northern Territory
and well into Western Australia, with toads on the
invasion front moving up to 60km a year.
They number in the 10s or even 100s of millions.
And everywhere they go, they wreak havoc on wildlife,
thanks to the poison glands on their shoulders that
are lethal for many animals that eat them.March of the cane toads
Introduced as a way to save sugarcane crops, cane toads are now a pest that’s
damaging local ecosystems. But we can slow their progress, reports Simon Webster.When toads arrive in a new area, the effect can be
devastating, particularly for apex predators.
“More than 95 per cent of goannas, blue tongue
skinks, freshwater crocodiles and northern quolls are
killed as soon as toads arrive,” Professor Rick Shine of
Macquarie University told a 2019 parliamentary inquiry
into controlling the spread of cane toads.
Shine notes that cane toads don’t kill everything:
some species (including native rats, insects and most
Australian birds) are immune to the poison. Native
frog populations appear to be unaffected, because the
bad effects (getting eaten by or poisoned by toads) are
balanced by the positives (fewer predators). Some
animals, such as some tropical snake species, grow
in numbers thanks to having fewer predators.
There is also evidence that vulnerable species can