FREE ESSAY ON THE AUSTRALIAN CANE TOAD

THE AUSTRALIAN CANE TOAD

THE AUSTRALIAN CANE TOAD
Introduction
The cane toad, Bufo marinus, or giant toad, was introduced to Australia by the sugar cane
industry with government sanction, in order to control two specific pests of sugar cane.
The grey backed cane beetle and the frenchie beetle. Native to Central and South America,
the cane toad has been introduced to several Pacific islands as well. One hundred and one
toads arrived at Edmonton in North Queensland in June 1935. About 11 sugar growing
locations in northern and central coastal Queensland received authorized shipments.
People at Normanton and Burketown, and in northern New South Wales deliberately released
the cane toad into the wild. Scientists warned the farmers not to bring the cane toad to
Australia but the farmers did not listen and brought them in anyway. 
Did the cane toad have any impact on the two cane beetles it was introduced to control?
Apparently not. The cane toad ate beetles when they were available, but as a control
agent, it had no impact at all. Instead of controlling certain insect populations, the
cane toad ate large numbers of bees and other beneficial insects. Within 5 years, an
effective insecticide became available and the sugar industry lost interest in the cane
toad. 
Although not native to Australia, the cane toad has one of the widest ranges of any
living toad. The species lives in a wide variety of habitats, but is restricted mainly by
the availability of water, since water is a vital element in the breeding cycle. However,
toads can survive near very small pools, or steams in arid regions. During the dry or
cold seasons, they remain inactive in shallow ground excavations beneath ground cover. 
Description 
Cane toads are very large and heavily built amphibians (up to 15 cm long) with warty
skin. The skin is strong, tough, and durable. Females tend to be larger and
smoother-skinned than males. Cane toads are olive-brown to reddish-brown on top, with a
paler white or yellowish belly. The underside is usually spotted with brown. The toad is
characterized by a stout body, which is heavier than that of frogs.
The most distinctive features of the cane toads are bony ridges over each eye and a pair
of enlarged glands, one on each shoulder. These glands are able to ooze venom. A
pronounced angular ridge runs between the eyes and snout. 
Giant toads can tolerate temperatures of 0 degrees Celsius to 41 degrees Celsius and are
able to survive high levels of dehydration. They can also adapt to different
temperatures. Their temperature and moisture tolerances may limit their distribution.
However, they do occur in warm temperate to semi-arid climates and are abundant in the
wet and dry tropics. A prediction, based on their ability to tolerate a variety of
climates, is that they will become established in Darwin early next century and
eventually spread over much of the coastal seaboard of Australia.
The call of the male cane toad is a high-pitched brrrr which sounds like a telephone dial
tone. The cane toad also has a distinctive stance and hop. It sits upright in an almost
vertical position and moves in a series of fast, short hops rather than long 'frog like'
hops. Also cane toads do not have webs between their toes.
Diet
Cane toads will eat almost any small creature they can catch. They eat whatever is
available. They often eat bees and dung beetles, small amphibians, reptiles, and mammals.
In fact, they eat any animal they can swallow. Unlike other amphibians, giant toads eat
things which do not move. They have also been known to steal food from dog and cat
bowls.
They have few predators native to Australia. The common Fresh Water Snake, (Tropidonophis
mairii), is the only Australian snake known to be able to feed on small cane toads
without dying as a result. Other native animals such as the estuarine crocodile, the
water rat and species of ibis are believed to feed on toads or on their internal organs.

Behavior and Breeding
Cane toads are highly adaptable, both in terms of survival and reproduction. They are
much more tolerant than other Australian frogs and can survive and breed in somewhat
salty water. In Australia, giant toads normally breed from June to January, but they have
been found in breeding condition throughout the year. Cane toads usually begin breeding
in their second summer, when they are about 75 mm long. The cane toad needs only a small
pool of water for breeding. The males fertilize the eggs as they are laid. Male toads
will attempt to mate with anything resembling a female toad - living or dead. As many as
35,000 eggs may be produced by each female, thus giving the species a high breeding
potential. Cane toad eggs are blackish in color and are deposited in long jelly like
strings onto plants, rocks or debris near water. The spawn consists of long double chains
of black eggs about 1 mm in diameter enclosed in a transparent cover.
Embryos begin hatching within 48 hours; after several days, the tadpoles begin feeding,
and the tail grows proportionately larger and hind limbs develop. In three days, the eggs
hatch into small (3 cm) jet black tadpoles - unlike those of any native frog. These
tadpoles become toadlets unusually early, so they are out of the water and hopping around
faster than most other frogs. Cane toad tadpoles differ further from most species in that
they occur in massive numbers and frequently form dense aggregations in shallow water. 
B. marinus adapted well to the Australian environment. So well that they are moving
closer to the wetlands of Kakadu National Park, which includes the Katherine Gorge.
District park manager John De Koning says wildlife like crocodiles, goannas, and snakes
will be threatened by the arrival of the non-native pest, even though they have only
found a few so far. We came across one large female, this was right on the very southern
eastern edge of the Nitmiluk National Park. We came across one female and we could hear
several males in the distance. The natural rate of spread of the cane toad is now 30-50
km/year in the Northern Territory and about 5 km/year in northern New South Wales. 
Finally, because their diet is so variable, they do not need to expend much energy
searching for food. They can just sit in a convenient spot, and gobble up anything that
wanders by. In urban areas, they are often seen gathered around street lamps eating
insects attracted by the light
Defense 
One of the most important factors in the success of the cane toad is that they are highly
poisonous to eat, at every stage of their life cycle. All frogs and toads may have
enlarged chemical-secreting glands at particular points on their bodies, or small glands
spread over the whole skin. The cane toad is one such amphibian. These secrete white
venom when the animal is handled or threatened. The eggs and tadpoles are also poisonous
and can cause cardiac arrest and death. 
A cane toad's reaction to a threat is to turn side-on to its attacker so that the venom
glands face them. The glands on the cane toad's shoulders are also capable of oozing
venom or even squirting it over a distance of up to 2m. Animals picking up a cane toad
and receiving a dose of venom may die within fifteen minutes. This venom is composed
mainly of cardioactive (affecting the heart) substances. 
The biggest danger to humans is that the venom could come in contact with the eyes, where
it causes intense pain and temporary blindness. Under pressure cane toads can shoot their
venom a short distance. This substance may be splashed into a person's mouth or eyes as
they attempt to kill the toad. Since the poison can be absorbed into the system through
mucus membranes, without ever being swallowed. Therefore, the mouth, eyes, and nose
should always be rinsed thoroughly if contact with venom occurs. 
Experiments and observations indicate that a variety of native animal life are extremely
susceptible to the many poisons in the cane toad's venom. These include avid frog eaters
such as the Tiger and Red bellied Black Snakes and the quolls. In areas where toads
appear, there has been a subsequent decline in populations of these types of native
animals, although more research is needed in this field. 
Research and Control
The CSIRO Australian Animal Health Laboratory (AAHL) at Geelong is a high security
microbiological facility, purpose designed and operated to undertake research into
viruses, bacteria, fungi and parasites which are exotic and do not occur in Australian
domestic or wild animals. It is the only laboratory of its kind in Australia where
studies on these exotic micro-organisms can be undertaken. Recently, the laboratory has
been commissioned and funded to begin research into the control of the cane toad, using
viruses or other microbial agents found overseas. 
The major concerns about the toad involve its prodigious appetite, and the toxicity of
all its life stages to native animals. There are firmly held beliefs that these
characteristics of the cane toad are responsible for the deaths of Australian wildlife
including herpetofauna, mammals, and fish. The toad will almost certainly establish
itself throughout the sensitive wetlands of northern Australia. The Australian Government
has provided significant funds to gather data to determine whether the toad has an impact
on the Australian environment and whether a biological control agent is required. The
funding also encompasses the search for and assessment of possible control agents. 
Funding of the project is distributed through the CSIRO Division of Wildlife Ecology,
Canberra, upon the advice of the Cane Toad Research Advisory Committee. Current work to
investigate the control of the cane toad by biological means has evolved from extensive
studies over the past decade which have gathered basic ecological and disease data for
the species. Such studies have been conducted in Australia, Venezuela, and Brazil. A
search for microbial agents with potential for control of toads has recently been
concluded in Venezuela. Research into the potential of viruses to control cane toads
involved isolating and purifying viruses from cane toads in their native habitats of
Venezuela, in South America. The effects of the viruses on cane toads and native frog
species were then tested in the secure biocontainment facilities at the CSIRO Australian
Animal Health Laboratory. Dr Alex Hyatt from CSIRO Animal Health says viruses isolated
from Venezuelan cane toads were compared with other viruses of the same family from
around the world, and are believed to fall within a new species of virus. While the
viruses proved effective in killing cane toad tadpoles, they also killed one species of
Australian frog in the trial. The team also found a small percentage of Australian cane
toads in the wild had been exposed to a virus similar to the Venezuelan viruses, which
are known to cause disease and death in fish and amphibian populations in Australia and
overseas. This adds another dimension to the potential impact of cane toads on the
Australian environment, Dr Hyatt says. 
As part of the work, the researchers also identified two fungal pathogens that are lethal
to cane toads and other amphibians. One fungus is thought to be responsible for frog
fatalities in Australia and Panama. Research also shows a small number of Australian cane
toads may be carrying a virus similar to the Venezuelan viruses, which could affect
Australian wildlife. 
CSIRO scientists have ruled out the use of viruses from Venezuela to control cane toads
in Australia because laboratory trials show that the viruses can also kill native
Australian frogs as well as the toads. 
At AAHL, a specialized group has been formed bringing together expertise in virology,
aquatic animal pathology, electron microscopy, and molecular biology. Expertise in the
group has resulted in the isolation of previously unknown disease causing agents in
Queensland. 
The objective of the current project is to find exotic, infectious microbial agents which
may spread throughout cane toad populations in Australia and decrease their numbers. The
project is also assessing the effects of these agents on adult, metamorphic, and juvenile
life stages of the toad, since it is likely that different life stages have differing
weaknesses.
Further research is being undertaken by CSIRO. Giant toads are often transported in
shipments of fruit and other commodities. Until effective control methods are available,
quarantine checks and the destruction of any accidental releases of toads are essential
to reduce their rate of spread.
Challenge experiments have commenced to evaluate the effects of viruses on toads. These
experiments are conducted under maximum microbiological security to ensure that escape of
the viruses cannot occur. Toads are maintained in laminar flow cabinets, within sealed
rooms. The air pressure of the rooms is lower than atmospheric pressure; thus ensuring
all air movement is into the room. Air leaving the room is double filtered to eliminate
the smallest viral particle from escaping. Water from the room is heated to kill any
infectious agents. Entrance to the room is through an air-lock and exit of personnel from
the room requires a full three minute shower. 
In association with the challenge experiments is a spectrum of microbiological,
serological, and molecular studies to characterize and compare the agents under
investigation, to establish information on the host's resistance to infection, and to
gather information related to similar agents in toads and other amphibian populations.
Should an agent be found which offers the potential for control of the toad, an extensive
series of subsequent studies is planned. To achieve the objectives of the project,
amphibian populations from around the world are being studied for possible infectious
agents. An international network of scientists, scientific institutions, interest groups
and interested individuals is being developed for information exchange relating to
diseases and population declines of amphibians. 
Potential for biological control of the toad is considered good, as the toad is the only
representative of the bufonid family in Australia and is distinct from other Australian
amphibian species. In addition, many species of the genus Bufo exist overseas, offering
exciting prospects that an infectious or parasitic agent from these may cause disease in
Australian Bufo marinus, without affecting native species.
It is hoped that these studies will provide valuable information on the causes of, and
initiating factors behind, the recent declines in frog populations in Australia, Britain
and elsewhere. Also, to contribute to the possibility that an infectious agent might be
found that would control cane toads in Australia. They are constantly looking for
possible pathogens for consideration for the biological control of cane toads. 
Finally, Chinese medicine manufacturers have been using the toads for centuries in the
treatment of Cardio Vascular Diseases and Cancer treatment. It is highly likely that the
cane toad will one day be farmed in Queensland for production of therapeutic medicines.
Conclusion
There is still much work to be done to fully understand what effects cane toads have on
native wildlife, and just how far they can spread. There are some reasons for optimism.
In the areas where cane toads have been around for the longest time, their populations
have declined after the initial population explosion. It is also possible that some
native animals are learning to avoid eating them. Other animals have shown they can eat
the toad. The Keelback Snake can detoxify the venom and Water Rats, Ibis, Crows and other
birds turn the toads over and eat only the non-poisonous internal organs. Opinion is
divided concerning their current status, some think the native wildlife is starting to
recognize them as a threat and they stay away.
Australia is still a long way from controlling cane toad numbers or putting a stop to
their expansion. Scientific evidence suggests that this imported animal represents a
nuisance to man and an ecological threat to the Australian environment. The rapid growth
of the species may have consequences in areas considered irrelevant at the time of its
introduction. The cane toad has provided a painful lesson in what can happen to native
species when an exotic species is introduced to a new habitat.