Why were cane toads introduced in Australia?
Cane toads were imported by the Australian Bureau of Sugar
Experimental Stations to eat cane beetles. The beetles were a major
pest of sugar cane and threatened to ruin the industry. The
Greyback and French's Cane Beetles, native insects that naturally
ate grass roots, bored into the roots of sugar cane crops and were
causing the plants to die and go brown. Control with poisons like
arsenic trioxide, carbon disulfide and even 1,4 dichlorobenzene was
failing badly, and the success of biological control against he
prickly pear led influential politicians and the CSIR to believe
the toad would eat the beetles.
Unfortunately, toads cannot access adult beetles which fly away
and the larvae live underground, so the experiment was a failure.
European common toads (Bufo bufo) were tested for
controlling grass grubs, but it was found they could not dig down
to reach them - a basic quarantine process never done with
Since none of Australia's native animals have resistance to
bufotenin (unlike other places where cane toads have been
introduced), they have become more of a pest than the beetles ever
were. Quolls, medium-sized carnivorous marsupials, have been very
badly hit by poisoning from toads and now are largely confined to
Tasmania where toads cannot reach (they sink in seawater). Many
snakes have also declined badly where toads are present.
Fertility control methods, though as yet unproven despite years
of research, offer the only hope for control. However, I do not
even know basic questions on this issue like how long poisonous
toad eggs remain viable without sperm to fertilise them - I have
assumed they would eventually die in the absence of sperm, but I
have not found data.