Monitor lizards are in the genus Varanus, the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the southern United States as an invasive species.
Monitor lizards have long necks, powerful and claws, and well-developed limbs. The adult length of extant species ranges from in some species such as Varanus sparnus, to over in the case of the Komodo dragon, though the extinct megalania ( Varanus priscus) may have reached lengths of more than . Most monitor species are terrestrial, but many are also arboreal or semiaquatic. While most monitor lizards are carnivorous, eating smaller reptiles, fish, , , small mammals, and eggs, a few species also eat fruit and vegetation.
Etymology
The
genus name
Varanus is derived from the Arabic word ورل
waral (Standard Arabic, colloquially ورر
warar or ورن
waran), from a common Semitic root
ouran,
waran,
warar or
waral, meaning "lizard beast".
In English, they are known as "monitors" or "monitor lizards". The earlier term "monitory lizard" became rare by about 1920.[ Google ngrams] The name may have been suggested by the occasional habit of varanids to stand on their two hind legs and to appear to "monitor",[Horatio Nelson, Matthew Henry Barker, The Life of Nelson Revised and Illustrated. With Original Anecdotes, Notes, Etc. By the Old Sailor, 1836 p. 35] But all of these explanations for the name "monitor" postdate Linnaeus giving the scientific name Lacerta monitor to the Nile monitor in 1758, which may have been based on a mistaken idea by Carl Linnaeus that the German word Waran (borrowed from Arabic) was connected to warnen (to warn), leading him to incorrectly it as monitor ('warner' or 'adviser').
Austronesian languages spoken across Southeast Asia, where varanids are common, have a large number of slightly related local names for them. They are usually known as biawak (Malay language, including Indonesian standard variety), bayawak (Filipino), binjawak or minjawak or nyambik (Javanese), or variations thereof.
In South Asia, they are known as in Meitei language, mwpou in Boro, (घोरपड) in Marathi language, (உடும்பு) in Tamil language and udumbu (ഉടുമ്പ്) in Malayalam, in Bhojpuri, gohi (गोहि) in Maithili, in Sinhala language as තලගොයා / කබරගොයා (), in Telugu language as uḍumu (ఉడుము), in Kannada language as (ಉಡ), in Punjabi language and Magahi as goh (गोह), in Assamese as gui xaap, in Odia language as godhi (ଗୋଧି), and in Bengali language as () (গোসাপ) or () (গুইসাপ), as goh (गोह) in Hindi language, and godhā (गोधा) in Sanskrit.
The West African Nile monitor is known by several names in Yoruba language, including , , and . In Serer language[Kesteloot, Lilyan, Dieux d'eau du Sahel: Voyage à travers les mythes de Seth à Tyamaba. Editions L'Harmattan, 2007, p. 11, [3] (accessed 27 March 2025)] and amongst the Wolofization Serer people[Diop, Cheikh Anta, The Cultural Unity of Black Africa: The Domains of Patriarchy and of Matriarchy in Classical Antiquity. Third World Press, 1978, p. 190, ] which is one of the many Serer maternal clans. The mbossé or mbosseh (in Gambian English) is one of the Serer religious festivals,[ Niang, Mor Sadio, in Ethiopiques numéro 31" - révue socialiste de culture négro-africaine 3e trimestre, IFAN, (1982) [4] .] and should not be confused with the mythical and sacred tree mbos―enshrined in Serer religion and Serer cosmogony―where the mbossé (the lizard) takes its name.
Due to confusion with the large New World lizards of the family Iguanidae, the lizards became known as "goannas" in Australia. Similarly, in South African English, they are referred to as leguaans, or likkewaans, from the Dutch language term for the Iguanidae, leguanen.
Distribution
The various species cover a vast area, occurring through Africa, the Indian subcontinent, to
China, the
Ryukyu Islands in southern
Japan, south to
Southeast Asia to
Thailand,
Malaysia,
Brunei,
Indonesia, the
Philippines,
New Guinea,
Australia, and islands of the
Indian Ocean and the South China Sea. They have also been introduced outside of their natural range, for instance, the West African Nile monitor is now found in
South Florida.
Monitor lizards also occurred widely in Europe in the
Neogene, with the last known remains in the region dating to the Middle Pleistocene.
Habits and diet
Most monitor lizards are almost entirely carnivorous,
consuming prey as varied as insects,
,
,
,
, fish,
, reptiles, birds, and mammals. Most species feed on invertebrates as juveniles and shift to feeding on vertebrates as adults. Deer make up about 50% of the diet of adult Komodo dragons, the largest monitor species.
In contrast, three
arboreal species from the Philippines,
Varanus bitatawa,
Varanus mabitang, and
V. olivaceus, are primarily
frugivore.
Biology
Monitor lizards are considered unique among animals in that its members are relatively morphologically conservative, yet show a very large size range.
However, finer morphological features such as the shape of the skull and limbs do vary, and are strongly related to the ecology of each species.
Like snakes, monitor lizards have highly forked tongues that act as part of the "smell" sense, where the tips of the tongue carry molecules from the environment to the a sensory organ in the skull called the Jacobson's organ. The forked apparatus allows for these lizards to sense boundaries in the molecules they collect, almost smelling in "stereo".
Monitor lizards are oviparous,[
]
(in Indonesian) which they often cover with soil or protect in a hollow tree stump. Some species, including the Komodo dragon, are capable of parthenogenesis.
Venom
Anatomical and molecular studies indicate that most if not all
Varanidae are
.
[
][
] Unlike snakes, monitor lizard venom glands are situated in their lower jaw.
The venom of monitor lizards is diverse and complex, as a result of the diverse ecological niches monitor lizards occupy.
For example, many species have anticoagulant venom, disrupting clotting through a combination of fibrinogenolysis and blocking platelet aggregation. Amongst them, arboreal species, such as the tree monitors and the banded monitor, have by far the strongest fibrinogenolytic venom. As a result, wounds from monitor lizard bites often bleed more than they would if they were simply lacerations. Venom may also cause hypotension.
In some species such as the Komodo dragon and the desert monitor, venom also induces a powerful neurotoxic effect. In the latter species for instance, envenomation causes immediate paralysis in rodents (but not birds) and lesser effects of the same nature in humans.
Metabolism
Monitor lizards maintain large territories and employ active-pursuit hunting techniques that are reminiscent of similar-sized mammals.
[King, D., Green, B., Knight, F. (1999). Monitors: The Biology of Varanid Lizards. Florida. Krieger Publishing Company.] The highly active nature of monitor lizards has led to numerous studies on the metabolic capacities of these lizards. The general consensus is that monitor lizards have the highest standard metabolic rates of all
Extant taxon reptiles.
[Pianka, E.R., Vitt, L.J. (2003). Lizards: Windows to the Evolution of Diversity. California. University of California Press.]
Monitor lizards have a high aerobic scope
Intelligence
At least some species of monitors are known to be able to count; studies feeding
varying numbers of snails showed that they can distinguish numbers up to six.
have been observed to cooperate when foraging; one animal 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.
[King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. , p. 43.][Pianka, E.R.; King, D.R. and King, R.A. (2004). Varanoid Lizards of the World. Indiana University Press.] at the National Zoo in Washington, DC, recognize their keepers and seem to have distinct personalities.
and green tree monitors in British zoos have been observed shredding leaves, apparently as a form of play.
Human uses
As pets
Monitor lizards have become a staple in the
reptile pet trade. The most commonly kept monitors are the
savannah monitor and Ackie dwarf monitor, due to their relatively small size, low cost, and relatively calm dispositions with regular handling. Among others, black-throated,
Timor monitor, Asian water,
Nile monitor,
mangrove monitor, emerald tree, black tree, roughneck, Dumeril's, peach-throated, crocodile, and
Argus monitor monitors have been kept in captivity.
Traditional medicines
Monitor lizards are poached in some South- and Southeast Asian countries, as their organs and fat are used in some traditional medicines, although there is no scientific evidence as to their effectiveness.
The dried and dyed
Hemipenis of
Bengal monitor, and less often
Yellow monitor and water monitors, are frequently trafficked and illegally sold in India and online under the deceptive term 'Hatha Jodi', where it is claimed to be the root of a supposed rare Himalayan plant in order to fool buyers and retailers, and to disguise the trade from wildlife authorities. Sellers advertise 'Hatha Jodi' as having the
Tantra power to bring wealth, power and contentment. A pair of hemipenes may sell at a value of up to US$250.
In India, the body oil of monitor lizards is sold for thousands of
Indian rupee to residents in metropolitan cities as a treatment for
rheumatism.
Monitor lizard meat, particularly the tongue and liver, is eaten in parts of India and Malaysia and is supposed to be an aphrodisiac.[ Eating Biawak. The Malaysian Life (April 2009)]
Consuming raw blood and flesh of monitor lizards has been reported to cause meningoencephalitis, as some monitors are hosts for the parasitic nematode Angiostrongylus cantonensis.
Leather
"Large-scale exploitation" of monitor lizards is undertaken for their skins, which are described as being "of considerable utility" in the leather industry. In Papua New Guinea, monitor lizard leather is used for membranes in traditional drums (called
kundu), and these lizards are referred to as
kundu palai or "drum lizard" in
Tok Pisin, the main Papuan trade language. Monitor lizard skins are prized in making the resonant part of serjas (Bodo folk sarangis) and dotaras (native strummed string instruments of Assam, Bengal and other eastern states). The leather is also used in making a
Carnatic music percussion instrument called the
kanjira.
Food
The meat of monitor lizards is eaten by some tribes in India,
Nepal,
the Philippines, Australia, South Africa, and West Africa as a supplemental meat source. Both meat and eggs are also eaten in Southeast Asian countries such as Vietnam and Thailand as a delicacy.
Conservation
According to IUCN Red List of threatened species, most of the monitor lizards species fall in the categories of least concern, but the population is decreasing globally. All but five species of monitor lizards are classified by the
CITES 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 to avoid use incompatible with the survival of the species in the wild. The remaining five species – the
Bengal monitor,
yellow monitor,
desert monitor, and clouded monitors and the Komodo Dragon– are classified under CITES Appendix I, which outlaws international commercial trade in the species.
The yellow monitor is protected in all countries in its range except Bhutan, Nepal, India, Pakistan, and Bangladesh.
In Kerala, Andhra Pradesh, Karnataka, Telangana and all other parts of South India, catching or killing of monitor lizards is banned under the Protected Species Act.
Evolution
Varanus is the only living genus of the family
Varanidae. Varanids last shared a common ancestor with their closest living relatives, earless "monitors", during the
Late Cretaceous. The oldest known varanids are from the
Late Cretaceous of Mongolia. During the
Eocene, the varanid
Saniwa occurred in North America. The closest known relative of
Varanus is
Archaeovaranus from the Eocene of China, suggesting that the genus
Varanus is of Asian origin. The oldest fossils of
Varanus date to the early
Miocene.
Many of the species within the various Subgenus also form with each other:
Euprepriosaurus
-
V. doreanus species complex ( V. doreanus, V. finschi, V. semotus, Varanus yuwonoi)
-
V. jobiensis species complex ( V. jobiensis)
Odatria
Varanus
-
V. gouldii species complex ( Sand goanna, V. rosenbergi, V. panoptes)
Polydaedalus
Empagusia
Soterosaurus
-
V. salvator species complex ( V. salvator, V. cumingi, V. nuchalis, V. togianus, V. marmoratus)
The tree monitors of the V. prasinus species complex ( V. prasinus, V. beccarii, V. boehmei, V. bogerti, Canopy goanna, V. kordensis, Varanus macraei, V. reisingeri, V. telenesetes) were once in the subgenus Euprepriosaurus, but as of 2016, form their own subgenus Hapturosaurus.
V. jobiensis was once considered to be a member of the V. indicus species complex, but is now considered to represent its own species complex.
+
Phylogeny as of Brennan et al. 2020 |
| |
Taxonomy
Genus Varanus
- Species marked with are Extinction
Subgenus Empagusia:
Subgenus Euprepiosaurus:[Ziegler, Thomas; Schmitz, Andreas; Koch, Andre; Böhme, Wolfgang (2007). "A review of the subgenus Euprepiosaurus of Varanus (Squamata: Varanidae): morphological and molecular phylogeny, distribution and zoogeography, with an identification key for the members of the V. indicus and the V. prasimus species groups". Zootaxa 1472: 1-28.]
-
Varanus bennetti, Bennett's long-tailed monitor
-
V. caerulivirens, Turquoise monitor
-
V. cerambonensis, Ceram monitor
-
Varanus colei Kei Islands monitor
-
Varanus doreanus, Blue-tailed monitor
-
Varanus douarrha, New Ireland monitor
-
Varanus finschi, Finsch's monitor
-
Varanus indicus, Mangrove monitor
-
V. jobiensis, Peach-throated monitor
-
V. juxtindicus, Rennell Island monitor
-
V. lirungensis, Talaud mangrove monitor
-
V. louisiadensis, Louisiade monitor
-
Varanus melinus, Quince monitor
-
Varanus obor, Sago monitor
-
V. rainerguentheri Rainer Günther's monitor
-
Varanus semotus, Mussau Island blue-tailed monitor
-
Varanus tanimbar, Tanimbar monitor
-
V. tsukamotoi, Mariana monitor
-
Varanus yuwonoi black-backed mangrove monitor, tricolor monitor
-
Varanus zugorum, Silver monitor, Zug's monitor
Subgenus Hapturosaurus:
-
Varanus beccarii, Black tree monitor
-
Varanus boehmei, Golden-spotted tree monitor
-
Varanus bogerti, Bogert's monitor
-
V. keithhornei, Canopy goanna, blue-nosed tree monitor, Nesbit River monitor
[ Varanus keithhornei, The Reptile Database]
-
V. kordensis, Biak tree monitor
-
Varanus macraei, Blue-spotted tree monitor
-
Varanus prasinus, Emerald tree monitor
[ Varanus prasinus, The Reptile Database]
-
V. reisingeri
[Eidenmüller, Bernd; Wicker, Rudolf (2005). " Eine weitere neue Waranart aus dem Varanus prasinus- Komplex von den Insel Misol, Indonesian ". Sauria 27 (1): 3-8. ( Varanus reisingeri, new species). (in German).] yellow tree monitor
-
V. telenesetes, mysterious tree monitor, Rossell tree monitor
Subgenus Odatria:
-
V. acanthurus, Spiny-tailed monitor, ridge-tailed monitor, Ackie's dwarf monitor
-
V. a. acanthurus, spiny-tailed monitor
-
V. a. brachyurus, common spiny-tailed monitor
-
V. auffenbergi, Auffenberg's monitor, peacock monitor
-
V. brevicauda, short-tailed monitor
-
Varanus bushi, Pilbara stripe-tailed monitor, Bush's monitor
-
V. caudolineatus, stripe-tailed monitor
-
Varanus citrinus, Gulf ridge-tailed monitor
-
Varanus eremius, rusty desert monitor, pygmy desert monitor
-
Varanus gilleni, pygmy mulga monitor
-
Varanus glauerti, Kimberley rock monitor
-
V. glebopalma, twilight monitor, black-palmed rock monitor
-
V. hamersleyensis, Hamersley Range rock monitor
-
V. insulanicus, Groote Eylandt monitor
-
V. i. baritji, black-spotted ridge-tailed monitor
-
Varanus kingorum, Kings' rock monitor
-
V. mitchelli, Mitchell's water monitor
-
Varanus ocreatus, Storr's monitor
-
V. pilbarensis, Pilbara rock monitor
-
V. primordius northern blunt-spined monitor
-
Varanus scalaris, banded tree monitor
-
V. semiremex rusty monitor
-
Varanus similis, Similis monitor, spotted tree monitor
-
Varanus sparnus, Dampier Peninsula monitor
-
Varanus storri, eastern Storr's monitor
-
V. timorensis, Timor monitor
-
Varanus tristis
-
V. t. tristis, black-headed monitor
-
V. t. orientalis, freckled monitor
Subgenus Papusaurus
-
V. salvadorii, Crocodile monitor
Subgenus Philippinosaurus:
-
V. bitatawa, northern Sierra Madre forest monitor, butikaw, bitatawa
-
Panay monitor, Panay monitor, mabitang
-
V. olivaceus, Gray's monitor, butaan
Subgenus Polydaedalus:
-
V. albigularis, Rock monitor, white-throated monitor
-
V. a. albigularis, White-throated monitor
-
V. a. angolensis, Angolan monitor
-
V. a. microstictus, Black-throated monitor
-
V. exanthematicus, Savannah monitor, Bosc's monitor
-
V. niloticus, Nile monitor
-
V. stellatus, West African Nile monitor
-
Varanus ornatus, Ornate monitor
-
V. yemenensis, Yemen monitor
Subgenus Psammosaurus:
-
desert monitor, Desert monitor
-
V. g. griseus, Desert monitor, grey monitor
-
V. g. caspius, Caspian monitor
-
V. g. koniecznyi, Indian desert monitor, Thar desert monitor
-
V. nesterovi, Nesterov's desert monitor
Subgenus Solomonsaurus:
-
V. spinulosus, Spiny-necked mangrove monitor, Solomon Islands spiny monitor
Subgenus Soterosaurus:
-
V. bangonorum, Bangon monitor
-
Varanus cumingi, Cuming's water monitor, yellow-headed water monitor
-
V. dalubhasa, Enteng's monitor
-
V. marmoratus, Marbled water monitor, Philippine water monitor
-
Varanus nuchalis large-scaled water monitor
-
V. palawanensis, Palawan water monitor
-
V. rasmusseni
[Koch, André; Gaulke, Maren; Böhme, Wolfgang (2010). "Unravelling the underestimated diversity of Philippine water monitor Lizards (Squamata: Varanus salvator complex), with description of two new species and a new subspecies". Zootaxa 2446: 1-54. ( Varanus rasmusseni, new species, p. 28).][ Varanus rasmusseni, The Reptile Database] Rasmussen's water monitor
-
V. rudicollis, Black roughneck monitor
-
V. salvator, Asian 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, Southeast Asian water monitor
-
V. s. ziegleri, Ziegler's water monitor
-
V. samarensis, Samar water monitor
-
Varanus togianus, Togian water monitor
Subgenus Varanus:
-
Perentie, Perentie
-
Sand goanna, Gould's monitor, sand monitor, sand goanna
-
Komodo dragon, Komodo dragon
-
V. mertensi, Mertens' monitor
-
Argus monitor
-
V. p. panoptes, Argus monitor
-
V. p. horni, Horn's monitor
-
V. p. rubidus, yellow-spotted monitor
-
Megalania, Megalania
-
V. rosenbergi, Rosenberg's monitor, heath monitor
-
Varanus spenceri, Spencer's monitor
-
Lace monitor, Lace monitor
Further reading
-
Blasius Merrem (1820). Versuchs eines Systems der Amphibien: Tentamen Systematis Amphibiorum. Marburg: J.C. Krieger. xv + 191 pp. + one plate. ( Varanus, new genus, p. 58). (in German and Latin).
External links
