Known prey organisms
Molecular Biology and Genetics
Statistics of barcoding coverage
|Specimen Records:||14||Public Records:||8|
|Specimens with Sequences:||11||Public Species:||4|
|Specimens with Barcodes:||10||Public BINs:||5|
|Species With Barcodes:||6|
Monitor lizards are generally large lizards, although some can be as small as 20 cm (7.9 in) in length. A total of 73 species are currently recognized; however, given that several species-groups are in need of taxonomic review, this number is certain to be increased with future research. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semiaquatic monitors are also known. While most monitor lizards are carnivorous, three arboreal species, Varanus bitatawa, Varanus mabitang, and Varanus olivaceus, are primarily frugivores. They are oviparous, laying from seven to 37 eggs, which they often cover with soil or protect in a hollow tree stump. Most species of monitor lizard have a predominantly carnivorous diet, eating eggs, smaller reptiles, fish, birds and small mammals. Some species of monitor lizard also eat fruit and vegetation depending on where they live.
The various species of Varanus cover a vast area, occurring through Africa, the Indian Subcontinent, to China, down Southeast Asia to Indonesia, the Philippines, New Guinea, Australia and islands of the Indian Ocean, and the South China Sea. A large concentration of monitor lizards occurs on Tioman Island in the Malaysian state of Pahang. Some are now found in South Florida, particularly in the Everglades, where they are becoming a dangerous threat to cattle and to other wildlife, including even alligators.
Monitor lizards differ greatly from other lizards in several ways, possessing a relatively high metabolic rate for reptiles, and several sensory adaptations that benefit the hunting of live prey. Recent research indicates the varanid lizards may have some venom. This discovery of venom in monitor lizards, as well as in agamid lizards, led to the Toxicofera hypothesis: that all venomous lizards and snakes share a common venomous ancestor.
Snakes were believed to be more closely related to monitor lizards than any other type of extant reptile; however, it has been more recently proposed that snakes are the sister group of the clade of iguanians and anguimorphs. Like snakes, monitor lizards have forked tongues which they use to sense odors.
During the Pleistocene epoch, giant monitor lizards lived in Southeast Asia and Australasia, the best known fossil being the megalania (Varanus priscus unless it falls in its own genus, in which case it is Megalania prisca). This species is an iconic member of the Pleistocene megafauna of Australia.
The generic name Varanus is derived from the Arabic word waral ورل, (alternative word waran). The name comes from a common Semitic root ouran, waran, or waral, meaning "lizard". The occasional habit of varanids to stand on their two hind legs and to appear to "monitor" their surroundings has been suggested to have led to this name, as it was Latinized into Varanus. Its common name is derived from the Latin word monere meaning "to warn".
In Austronesia where varanids are common, they are known under a large number of local names. They are usually known as biawak (Malay and Indonesian), bayawak (Filipino), binjawak or minjawak (Javanese), or variations thereof. Other names include hokai (Solomon Islands), bwo or puo (Maluku), halo (Cebu), galuf of kaluf (Micronesia and the Caroline Islands), batua or butaan (Luzon), alu (Bali), hora or ghora (Komodo group of islands), phut (Burmese) and guibang (Manobo).
In Tamil and Malayalam, monitor lizards are known as udumbu, ghorpad घोरपड in Marathi, uda in Kannada, in Sinhalese as kabaragoya, in Telugu as udumu, in Punjabi and Magahi (and other Bihari languages) as goh, in Assamese as gui xaap, and in Bengali as goshaap or guishaap and गोह (goh) in Hindi. Due to confusion with the large New World lizards of the family Iguanidae, the lizards became known as "goannas" in Australia. Similarly, in South Africa, they are referred to as leguaan, or likkewaan from the Dutch for iguana. The generic name inspired the name of the Japanese movie monster Varan.
Varanid lizards are very intelligent, and some species can even count. Careful studies feeding V. albigularis at the San Diego Zoo varying numbers of snails showed they can distinguish numbers up to six. V. niloticus lizards have been observed to cooperate when foraging. One varanid lures the female crocodile away from her nest, while the other opens the nest to feed on the eggs. The decoy then returns to also feed on the eggs. Komodo dragons, V. komodoensis, at the National Zoo in Washington, D.C., recognize their keepers and seem to have distinct personalities.
Monitor lizards have become a staple in the reptile pet trade. The most commonly kept monitors are the savannah monitor and Ackies monitor, due to their relatively small size, low cost, and relatively calm dispositions with regular handling. Black throated monitors, white throated monitors, water monitors, Nile monitors, mangrove monitors, emerald tree monitors, black tree monitors, acanthurus monitors, quince monitors, crocodile monitors and Komodo dragons have been kept in captivity. Like all reptiles kept as pets, monitors need an appropriately sized enclosure, hiding places, and an appropriate substrate. Some water monitors also need a large water dish in which they can soak their entire bodies. In the wild, monitors will eat anything they can overpower, but crickets, superworms, feeder fish, and the occasional rodent (for calcium) make up most of the smaller captive monitors' diets. Boiled eggs, silkworms, and earthworms can also be fed to them. Larger species, such as Nile monitors, Asian water monitors, crocodile monitors, perenties, and Komodo dragons, will eventually require larger prey. Paleontologist and biology professor at Temple University, Michael Balsai has observed V. prasinus eating fruit in captivity, as has herpetologist and author, Robert G. Sprackland.
In parts of Pakistan, different parts of monitor lizards are used for a variety of medical purposes. The flesh is eaten for relief of rheumatic pain, abdominal fat is used as a salve for skin infections, oil and fat are used to treat hemorrhoids or chronic pain, and the oil is used as an aphrodesiac lubricant.
"Large scale exploitation" of monitor lizards is undertaken for their skins, which are described as being "of considerable utility" in the leather industry.
All but five species of monitor lizard are classified by the Convention on International Trade in Endangered Species of Wild Fauna and Flora under Appendix II, which is loosely defined as species that are not necessarily threatened with extinction, but may become so unless trade in such species is subject to strict regulation order to avoid use incompatible with the survival of the species in the wild. The remaining five species - V. bengalensis, V. flavescens, V. griseus, V. komodoensis, and V. nebulosus - are classified under CITES Appendix I, which outlaws international commercial trade in the species.
In Tamil Nadu and all other parts of South India, catching or killing of monitor lizards is banned under the Protected Species Act.
- V. bengalensis, Bengal monitor
- V. b. bengalensis, Bengal monitor
- V. b. nebulosus or V. nebulosus, Clouded monitor
- V. dumerilii, Dumeril's monitor
- V. flavescens, Golden monitor
- V. rudicollis, Roughneck monitor
- V. beccarii, Black tree monitor
- V. boehmei, Golden-spotted tree monitor
- V. bogerti, Bogert's tree monitor
- V. caerulivirens, Turquoise monitor
- V. cerambonensis, Ceram monitor
- V. doreanus, Blue-tailed monitor
- V. finschi, Finsch's monitor
- V. indicus, Mangrove monitor
- V. jobiensis, Peach-throated monitor
- V. juxtindicus, Rennell Island monitor
- V. keithhornei, Canopy goanna, Nesbit River monitor
- V. kordensis, Biak tree monitor
- V. macraei, Blue-spotted tree monitor
- V. melinus, Quince monitor
- V. lirungensis, Talaud mangrove monitor
- V. obor, sago monitor
- V. prasinus, Emerald tree monitor
- V. rainerguentheri Rainer Günther’s monitor
- V. reisingeri, Reisinger's tree monitor
- V. telenesetes, Mysterious tree monitor, Rossell tree monitor
- V. yuwonoi, Tricolored monitor
- V. zugorum, Silver monitor, Zug's monitor
- V. acanthurus, Ridge-tailed monitor
- V. a. acanthurus, Ridge-tailed monitor
- V. a. brachyurus, Common ridge-tailed monitor
- V. a. insulanicus, Island ridge-tailed monitor
- V. auffenbergi, Auffenberg's monitor, Peacock monitor
- V. baritji, White's dwarf monitor, black-spotted ridge-tailed monitor, lemon-throated monitor
- V. brevicauda, Short-tailed monitor
- V. bushi, Pilbara stripe-tailed monitor, Bush's monitor
- V. caudolineatus, Stripe-tailed monitor
- V. eremius, Rusty desert monitor, pygmy desert monitor
- V. gilleni, Pygmy mulga monitor
- V. glauerti, Kimberley rock monitor
- V. glebopalma, Twilight monitor, black-palmed rock monitor
- V. hamersleyensis, Hamersley Range rock monitor
- V. kingorum, Kings' rock monitor
- V. mitchelli, Mitchell's water monitor
- V. pilbarensis, Pilbara rock monitor
- V. primordius, Blunt-spined monitor
- V. scalaris, Banded tree monitor
- V. semiremex, Rusty monitor
- V. similis, Spotted tree monitor
- V. storri, Storr's monitor
- V. s. storri, Eastern Storr's monitor
- V. s. ocreatus, Western Storr's monitor
- V. timorensis, Timor monitor
- V. tristis, Black-headed monitor
- V. t. orientalis, Freckled monitor
- V. salvadorii, Crocodile monitor
- V. bitatawa, Northern Sierra Madre forest monitor, bitatawa
- V. mabitang, Panay monitor
- V. olivaceus, Gray's monitor
- V. albigularis, White-throated monitor
- V. exanthematicus, Savanna monitor, Bosc's monitor
- V. niloticus, Nile monitor
- V. ornatus, ornate monitor
- V. yemenensis, Yemen monitor
- †V. darevskii (extinct)
- V. griseus, Desert monitor [endangered]
- V. g. griseus, Desert monitor, grey monitor
- V. g. caspius, Caspian monitor
- V. g. koniecznyi, Indian desert monitor, Thar desert monitor
- V. cumingi, Cuming's water monitor, yellow-headed water monitor
- V. c. cumingi, Cuming's water monitor
- V. c. samarensis, Samar water monitor
- V. marmoratus, Marbled water monitor, Philippine water monitor
- V. nuchalis, Large-scaled water monitor, white-headed water monitor, Negros water monitor
- V. palawanensis Palawan water monitor
- V. rasmusseni Rasmussen's water monitor
- V. salvator, Water monitor
- V. s. salvator, Sri Lankan water monitor
- V. s. andamanensis, Andaman water monitor
- V. s. bivittatus, Two-striped water monitor, Javan water monitor
- V. s. macromaculatus, Asian water monitor
- V. s. ziegleri, Ziegler's water monitor
- V. togianus, Togian water monitor
- V. giganteus, Perentie
- V. gouldii, Sand monitor, Gould's monitor
- V. komodoensis, Komodo dragon
- V. mertensi, Mertens' monitor
- V. panoptes
- V. p. panoptes, Argus monitor
- V. p. horni, Horn's monitor
- V. p. rubidus, Yellow-spotted monitor
- †V. priscus, Megalania (extinct)
- V. rosenbergi, Rosenberg's monitor, heath monitor
- V. spenceri, Spencer's monitor
- V. varius, Lace monitor
- Greene, Harry W. (1986). Diet and Arboreality in the Emerald Monitor, Varanus Prasinus, with Comments on the Study of Adaptation. Chicago: Field Museum of Natural History. OCLC 14915452. Retrieved 12 December 2013.
- Welton, L. J.; Siler, C. D.; Bennett, D.; Diesmos, A.; Duya, M. R.; Dugay, R.; Rico, E. L. B.; Van Weerd, M.; Brown, R. M. (2010). "A spectacular new Philippine monitor lizard reveals a hidden biogeographic boundary and a novel flagship species for conservation". Biology Letters 6 (5): 654–658. doi:10.1098/rsbl.2010.0119. ISSN 1744-9561. PMC 2936141. PMID 20375042.
- Bauer, Aaron M. (1998). Cogger, H.G. & Zweifel, R.G., ed. Encyclopedia of Reptiles and Amphibians. San Diego: Academic Press. pp. 157–159. ISBN 0-12-178560-2.
- Fry, B.G.; Wroe, S; Teeuwisse, W; van Osch, JP; Moreno, K; Ingle, J; McHenry, C; Ferrara, T; Clausen, P; Scheib, H; Winter, KL; Greisman, L; Roelants, K; van der Weerd, L; Clemente, CJ; Giannakis, E; Hodgson, WC; Luz, S; Martelli, P; Krishnasamy, K; Kochva, E; Kwok, HF; Scanlon, D; Karas, J; Citron, DM; Goldstein, EJC; Mcnaughtan, JE; Norman JA. (June 2009). "A central role for venom in predation by Varanus komodoensis (Komodo dragon) and the extinct giant Varanus (Megalania) priscus.". PNAS 106 (22): 8969–8974. doi:10.1073/pnas.0810883106. PMC 2690028. PMID 19451641.
- Fry, B.G.; Vidal, N; Norman J.A.; Vonk F.J.; Scheib, H.; Ramjan S.F.R; Kuruppu S.; Fung, K.; Hedges, B.; Richardson M.K.; Hodgson, W.C.; Ignjatovic, V.; Summerhays, R.; Kochva, E. (February 2006). "Early evolution of the venom system in lizards and snakes" (PDF). Nature 439 (7076): 584–588. doi:10.1038/nature04328. PMID 16292255.
- "Monitor Lizards". BBC Nature. BBC. Retrieved 2014-03-05.
- Smith, Kerri. "Dragon virgin births startle zoo keepers". Nature. Retrieved 2006-12-20.
- Robert George Sprackland (1992). Giant lizards. Neptune, NJ: T.F.H. Publications. p. 61. ISBN 0-86622-634-6.
- Mark K. Bayless (2004). "The local names of Pacific monitor lizards (Sauria: Varanidae) of Oceania & Indo-Malaysia, excluding Australia". Micronesia 37 (1): 49–55.
- Maren Gaulke (1992). "Taxonomy and biology of Philippine water monitors (Varanus salvator)". The Philippine Journal of Science 121 (4): 345–381.
- King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X, p. 43.
- Pianka, E.R.; King, D.R. and King, R.A. 2004. Varanoid Lizards of the World. Indiana University Press.
- Balsai, Michael (1997). The General Care and Maintenance of Popular Monitors and Tegus. BowTie. p. 6. ISBN 978-1-882770-39-7.
- Parameswaran, K (2006). "Case series of eosinophilic meningoencephalitis from South India". Annals of Indian Academy of Neurology 9 (4): 217–222. doi:10.4103/0972-2327.29203. ISSN 0972-2327. Retrieved 12 December 2013.
- Hashmi, M. Usman Ali; Khan, M. Zaheer; Amtyaz; Huda, Nawaz Ul. "Current Status, Distribution and Threats of Varanus Species (Varanus bengalensis & Varanus griseus) in Karachi & Thatta of Sindh". International Journal of Fauna and Biological Studies (AkiNik Publications) 1 (1): 34–38. ISSN 2347-2677. Retrieved 12 December 2013.
- "Identification Guides for Wildlife Traded in Southeast Asia". ASEAN-WEN. 2008.
- Varanus keithhornei, The Reptile Database
- Varanus prasinus, The Reptile Database
- Varanus baritji, The Reptile Database
- Varanus spinulosus, The Reptile Database
Not all goannas are gargantuan. Pygmy goannas may be smaller than a man's arm. The smallest of these, the short-tailed monitor (Varanus brevicuda) reaches only 20 cm in length. They survive on smaller prey, such as insects and mice.
Goannas combine predatory and scavenging behaviours. A goanna will prey upon any animal it can catch and is small enough to eat whole. Goannas have been blamed for the death of sheep by farmers, though most likely erroneously, as goannas are also eaters of carrion and are attracted to rotting meat.
Most goannas are dark in colouration, browns, blacks and greens featuring prominently. Many desert-dwelling species also feature yellow-red tones. Camouflage ranges from bands and stripes to splotches, speckles, and circles, and can change as the creature matures, with juveniles sometimes being brighter than adults.
Like most lizards, goannas lay eggs. Most lay eggs in a nest or burrow, but some species lay their eggs inside termite mounds. This offers protection and incubation; additionally, the termites may provide a meal for the young as they hatch. Unlike some other species of lizards, goannas do not have the ability to regrow limbs or tails.
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 amongst these, but is not the most common. The lace monitor is the second-largest of all goannas, reaching lengths of up to 2 m. 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, averaging only a few feet nose-to-tail.
Other goannas are adapted to swampy coastal environments, such as the mangrove goanna (V. semiremex). Further still, the 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 the water.
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 will feed on whatever prey items 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 will feed on the carcasses of dead animals, including livestock and other large creatures. The smell of rotting meat will attract these lizards.
Goannas and humans
Like most native fauna, goannas are rather wary of human intrusions into their habitat, and will 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, will sprint 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 recover from their initial fear of humans, especially when food is involved (or food has been involved previously). This reinforces the wildlife authority's recommendation of not feeding animals while camping or adventuring, but most authorities doubt a goanna will actually direct an intentional attack at a human unless the human attempts to attack it (or grasp at it) first. Aborigines who hunt goannas for food consider the perentie as a high-risk (but tasty) prey.
The debate on whether goannas are venomous or not is growing. Previously, the incessant bleeding caused by goanna bites was thought to be the result of bacterial infection. A recent study suggests 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; 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 off the ground to safety, which is understandably painful, as well as distressing for both man and beast.
Goannas are protected species throughout Australia.
Culture and folklore
Representations of goannas are common in indigenous artwork, not just as food, but also as a symbolic spiritual motif. Goannas and the mighty perentie are often considered two different animals when used in aboriginal works, as illustrated by 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 amongst campers and bushmen. This includes the above-mentioned exaggeration of goannas dragging off sheep from shepherds' flocks in the night. These might even be exaggerated into child-snatching, rivalling drop bears (attack koalas) as a tourist scarer, 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.
Because the goanna regularly eats snakes (often involving a fierce struggle between the two), they are often said to be immune to snake venom. The goanna does eat venomous snakes, but no evidence found suggests actual poison immunity. Other stories say the lizard eats a legendary plant, or drinks from a healing spring which neutralises the poison. This is immortalised in Banjo Paterson's humorous poem "Johnson's Antidote".
Possibly related to the above poison immunity, goanna fat or oil has been anecdotally imbued with mystical healing properties. Aborigines traditionally used goanna oil as an important bush medicine, and it also became a common medicine among whites in Australia's early days. Said to be a cure-all, and possessing amazing powers of penetration (passing through metal as if it were not there), it was sold amongst early settlers like snake oil in the Old West of North America.
In popular culture
Joanna the Goanna was featured in the movie The Rescuers Down Under as the cohort of poacher McLeach; she was a Spencer's goanna. A goanna was also voiced by African-American actor Tone-Loc in FernGully: The Last Rainforest. Goannas appear as enemies in the Ty the Tasmanian Tiger series by Krome Studios.
The name goanna might have been derived from iguana, as early European settlers likened goannas to the South American lizards. Over time, the initial vowel sound was dropped. A similar explanation is used to link possum to the American opossum.
Another possibility is the name might have been derived from the South African term for a monitor lizard, leguaan, as the Cape of Good Hope was a popular refresher stop for immigrant ships to Australia from Britain.
For the most part, in common names, "goanna" and "monitor" are interchangeable.
- Perentie – V. giganteus
- Lace monitor – V. varius
- Sand goanna – V. gouldii (also Gould's goanna or ground goanna)
- Mertens' water monitor – V. mertensi
- Spiny-tailed monitor – V. acanthurus (also ridge-tailed monitor)
- Mangrove monitor – V. semiremex
- Timor monitor – V. timorensis (also Timor monitor)
- Black-headed monitor – V. tristis
- Short-tailed monitor – V. brevicuda
- Argus monitor – V. panoptes (also yellow-spotted monitor)
- Black-tailed goanna – V. cookii
- Rosenberg's monitor – V. rosenbergi
- Spencer's goanna – V. spenceri
- Ehmann, Harald. Encyclopedia of Australian Animals: Reptiles. (1992), p. 144. Angus&Robertson, Pymble, Australia. ISBN 0-207-17379-6.
- Cogger, Harold (1978). Australian reptiles in colour. Terrey Hills, N.S.W.: Reed. p. 59. ISBN 0-589-50060-0.
- Andrew, Learmonth; Learmonth, Nancy (1973). Encyclopaedia of Australia ([2d ed.] ed.). London: F. Warne. p. 229. ISBN 0-7232-1709-2.
- Young E, Lizards' poisonous secret is revealed, New Scientist.com news service, 16 November 2005
- Goanna. Aboriginal Tourism - Indigenous Australia - Iconography and Symbols (Travel Australia with AusEmade).
- Goanna venom rocks the reptile record, UniNews Vol. 14, No. 22 28 November - 12 December 2005, University of Melbourne, Retrieved 8 March 2006
- 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
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