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Goanna
Several species of reptiles

Goannas are a group of carnivorous reptiles from the genus Varanus, with around 70 species, 25 native to Australia and Southeast Asia. They occupy diverse ecological niches and vary greatly in size, from the large perentie over 2.5 m long to the tiny short-tailed monitor, which grows to just 20 cm. Predatory and scavenging, goannas feed on small animals and carrion, occasionally blamed for killing sheep. Their coloration offers effective camouflage, ranging from greys and browns to yellows and reds. They lay eggs in nests or termite mounds, but unlike some lizards, they cannot regrow lost limbs. Goannas also hold significance in Australian folklore.

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Etymology

The name goanna is derived from iguana. Early European bush settlers in Australia likened goannas to the South American lizards.2 Over time, the initial vowel sound was dropped. A similar explanation is used to link possums to the American opossum.

The South African term for a monitor lizard is leguaan and this word is also from Spanish 'la iguana'.

Species

For a list of all monitor lizards of the genus, see Complete list of genus Varanus. The following are found in Australia. For the most part, in common names, "goanna" and "monitor" are interchangeable.

Habitats

Goannas are found throughout most of Australia, except for Tasmania, and manage to persist in a variety of environments. Most species are known to climb trees or outcrops; several primarily arboreal species are known. The lace monitor (V. varius) is probably the best-known among these, but is not the most common. The lace monitor is the second-largest of all goannas, reaching lengths up to 2 m (6.6 ft). Other more common tree goannas, such as the Timor tree monitor (V. timorensis) and mournful tree monitor (V. tristis,) do not grow to quite such lengths, typically a maximum of 61 cm, nose-to-tail.

Other goannas are adapted to swampy coastal environments, such as the mangrove goanna (V. semiremex). Further still, Mertens' water monitor (water goanna – V. mertensi), found in lagoons and rivers across northern Australia, is streamlined for swimming, using its tail as a paddle. Most other goannas are good swimmers, but tend not to voluntarily venture into water.

Diet

The diets of goannas vary greatly depending on the species and the habitat. Prey can include all manner of small animals: insects, smaller lizards, snakes, mammals, birds, and eggs.

Meals are often eaten whole, thus the size of their meals may depend on the size of the animals. Many of the small species feed mostly on insects, with some being small lizard experts. Many of the medium to large species feed on whatever prey they can catch. This includes eggs, fish (V. mertensi), birds, snails, smaller lizards, snakes, marsupials, and other small mammals, such as rodents. The giant perentie has been observed killing a young kangaroo, and then biting out chunks of flesh like a dog.

All species are carrion eaters, so feed on the carcasses of dead animals, including livestock and other large creatures.34 The smell of rotting meat also attracts these lizards.

Goannas and humans

Confrontations

Like most native fauna, goannas are rather wary of human intrusions into their habitat, and most likely run away (into the scrub, up a tree, or into the water, depending on the species). A goanna is a rather swift mover, and when pressed, sprints short distances on its hind legs.

Goannas also rear up when threatened, either chased or cornered, and also inflate flaps of skin around their throats and emit harsh hissing noises.

Some goannas lose their initial fear of humans, especially when food is involved (or has been previously involved). The wildlife authority recommends not feeding animals while in their territory. An attack can cause serious injury in exceptional cases,5 but most authorities doubt that a goanna will direct an intentional attack at a human unless the human has attempted to attack it (or grasp at it) first. Indigenous Australians who hunt goannas for food consider the perentie to be a high-risk (but tasty) quarry.

Debate is growing as to whether goannas are venomous. The incessant bleeding caused by goanna bites had been thought to be the result of bacterial infection, but a 2005 study6 suggested monitor lizards (including goannas) are venomous and have oral toxin-producing glands.

The goanna's hefty tail can be dangerous when swung, much like a crocodile's tail; small children and dogs have been knocked down by such attacks. Often victims in goanna attacks are bystanders, watching the person antagonising the goanna. Alarmed goannas can mistake standing humans for trees and attempt to climb them to safety, which is painful and can be distressing for both human and goanna.7

Conservation status

Goannas are protected species throughout Australia.8

Culture and folklore

Further information: Dirawong

Goannas have a prominent place in the culture of indigenous Australians. This includes totemic relationships, anthropomorphic representations in dreamtime stories, and as a food source. Representations of goannas are common in indigenous artwork, not just as food, but also as a symbolic spiritual motif. Smaller goannas and the mighty perentie are often considered two different animals when appearing in aboriginal works, as in the story "How the Goanna and Perentie Got Their Colours".

European settlers perpetuated several old wives' tales about goanna habits and abilities; some of these have persisted in modern folklore among campers and bushmen. This includes the above-mentioned exaggeration of goannas dragging off sheep from shepherds' flocks in the night. This might even be exaggerated into child-snatching, rivalling drop bears (attack koalas) as a tourist scarer, but probably more convincing due to the reptiles' carnivorous nature and fearsome appearance.

A common tale was that the bite of a goanna was infused with a powerful, incurable venom. Every year after the bite (or every seven years), the wound would flare up again. For many years, herpetologists generally believed goannas were nonvenomous, and lingering illness from their bites was due solely to infection and septicaemia as a result of their saliva being rife with bacteria from carrion and other food sources. However, in 2005, researchers at the University of Melbourne announced that oral venom glands had been found in both goannas and iguanas.9

Because the goanna regularly eats snakes (which may involve a fierce struggle), including venomous species, they are often said to be immune to snake venom. However, no evidence found suggests an actual venom immunity. Other stories say that the lizard eats a legendary plant, or drinks from a healing spring, which neutralises the venom. (This idea is immortalised in Banjo Paterson's humorous poem "Johnson's Antidote".)

Goanna fat or oil has been anecdotally imbued with mystical healing properties (possibly in connection with their supposed venom immunity). Aboriginal people traditionally used goanna oil as an important bush medicine, and it also became a common medicine among Caucasians shortly after British settlement in Australia. Said to be a cure-all, and possessing amazing powers of penetration (passing through metal as if it were not there), it was sold among early settlers like snake oil in the Old West of North America.

A goanna features as the heroic figure Mr Lizard in the Australian author May Gibbs’ children's books Snugglepot and Cuddlepie. A bronze statue of the goanna Mr Lizard has been placed outside the State Library of Victoria.

The villain in the Disney film The Rescuers Down Under, Percival C. McLeach, has a pet goanna named Joanna.

Further reading

  • Cogger, H. (1967). Australian Reptiles in Colour. Sydney: A. H. & A. W. Reed, ISBN 0-589-07012-6
  • King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X
  • Underhill, D. (1993). Australia's Dangerous Creatures. Sydney: Reader's Digest. ISBN 0-86438-018-6

References

  1. Ehmann, Harald. Encyclopedia of Australian Animals: Reptiles. (1992), p. 144. Angus&Robertson, Pymble, Australia. ISBN 0-207-17379-6. /wiki/ISBN_(identifier) ↩

  2. MacDonald, Donald (19 January 1917). "Nature Notes and Queries: Goanna or Iguana". The Argus (Melbourne). No. 21, 990. Victoria, Australia. p. 5. Retrieved 8 November 2018 – via National Library of Australia. http://nla.gov.au/nla.news-article1591315 ↩

  3. Cogger, Harold (1978). Australian reptiles in colour. Terrey Hills, N.S.W.: Reed. p. 59. ISBN 0-589-50060-0. 0-589-50060-0 ↩

  4. Andrew, Learmonth; Learmonth, Nancy (1973). Encyclopaedia of Australia ([2d ed.] ed.). London: F. Warne. p. 229. ISBN 0-7232-1709-2. 0-7232-1709-2 ↩

  5. Naaman Zhou (16 August 2019). "Goanna attack: Queensland couple in hospital after 'freak ordeal'". The Guardian. https://www.theguardian.com/australia-news/2019/aug/16/goanna-attack-dog-killed-and-queensland-couple-in-hospital-after-freak-ordeal ↩

  6. Emma Young (16 November 2005). "Lizards' poisonous secret is revealed". New Scientist. Retrieved 16 August 2019. https://www.newscientist.com/article/dn8331-lizards-poisonous-secret-is-revealed/ ↩

  7. Underhill D (1993) Australia's Dangerous Creatures, Reader's Digest, Sydney, New South Wales, ISBN 0-86438-018-6 /wiki/ISBN_(identifier) ↩

  8. "Monitor Lizards". www.wires.org.au. Retrieved 1 March 2023. https://www.wires.org.au/wildlife-information/monitor-lizards ↩

  9. Goanna venom rocks the reptile record Archived 24 August 2006 at the Wayback Machine, UniNews Vol. 14, No. 22 28 November - 12 December 2005, University of Melbourne, Retrieved 8 March 2006 http://uninews.unimelb.edu.au/articleid_3009.html ↩