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The Bengal monitor (''Varanus bengalensis''), also called the common Indian monitor, is a monitor lizard distributed widely in the
Indian Subcontinent The Indian subcontinent is a list of the physiographic regions of the world, physiographical region in United Nations geoscheme for Asia#Southern Asia, Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian O ...
, as well as parts of
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainlan ...
and
West Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion of the larger geographical region of Asia, as defined by some academics, UN bodies and other institutions. It is almost entirely a part of the Middle East, and includes Ana ...
. This large lizard is mainly a
terrestrial animal Terrestrial animals are animals that live predominantly or entirely on land (e.g. cats, dogs, ants, spiders), as compared with aquatic animals, which live predominantly or entirely in the water (e.g. fish, lobsters, octopuses), and amphibian ...
, and its length ranges from about from the tip of the snout to the end of the tail. Young monitors may be more
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...
, but adults mainly hunt on the ground,
prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
ing mainly on arthropods, but also taking small terrestrial
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s, ground
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s,
eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
and
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...
. Although large Bengal monitors have few
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
s apart from humans who hunt them for meat, younger individuals are hunted by many predators.


Description

The Bengal monitor can reach 175 cm with a snout-to-vent length (SVL) of 75 cm and a tail of 100 cm. Males are generally larger than females. Heavy individuals may weigh nearly 7.2 kg. The populations of monitors in India and Sri Lanka differ in the scalation from those of Myanmar; these populations were once considered subspecies of the Bengal monitor, but are now considered two species within the ''V. bengalensis'' species complex. What was once the nominate subspecies, ''V. bengalensis'', is found west of Myanmar, while the clouded monitor (''V. nebulosus'') is found to the east. Clouded monitors can be differentiated by the presence of a series of enlarged scales in the supraocular region. The number of ventral scales varies, decreasing from 108 in the west to 75 in the east (Java). Young monitor lizards are more colourful than adults. Young have a series of dark crossbars on the neck, throat and back. The belly is white, banded with dark crossbars and are spotted with grey or yellow (particularly in the eastern part of the range). On the dorsal surface of young monitors, there are a series of yellow spots with dark transverse bars connecting them. As they mature, the ground colour becomes light brown or grey, and dark spots give them a speckled appearance. Clouded monitor hatchlings by comparison tend to have a series of backward-pointing, V-shaped bands on their necks. Bengal monitors have external nostril openings (nares) that is slit-like and oriented near horizontal, and positions between the eye and the tip of the snout. The nares can be closed at will, especially to keep away debris or water. The scales of the skin are rougher in patches and on the sides, they have minute pits, especially well distributed in males. These scales with micropores have glandular structures in the underlying dermal tissue and produce a secretion which may be a pheromone-like substance. Like other monitors, Bengal monitors have a forked tongue similar to snakes. The function is mainly sensory, and is not very involved in the transport of food down the throat. Bengal monitors have fat deposits in the tail and body that serve them in conditions when prey are not easily available. The lungs have spongy tissue unlike the sacs of other saurians. This allows for a greater rate of gas exchange and allows a faster metabolic rate and higher activity levels. Like all monitors, they have subpleurodont teeth, meaning the teeth are fused to the inside of the jaw bones. The teeth are placed one behind another, and there are replacement teeth behind and between each functional tooth (polyphyodont). The maxillary and dentary teeth are laterally compressed, sometimes with a slightly serrate cutting edge, while the premaxillary teeth are conical. There are 78 premaxillary teeth, 10 maxillary and 13 dentary teeth. Replacement teeth move forward and about four replacements happens each year for a tooth. While monitor lizards are venomous, there are no reports of the effects of venom in Bengal monitors other than a very controversial case report of fatal renal failure as a result of envenomation from this species.


Distribution and habitat

The species ranges from Iran to Java, among the most widely distributed of monitor lizards as they are eurytopic and adaptable to a range of habitats. It is found in river valleys in eastern
Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...
,
Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan,; prs, امارت اسلامی افغانستان is a landlocked country located at the crossroads of Central Asia and South Asia. Referred to as the Heart of Asia, it is bordere ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
,
Nepal Nepal (; ne, :ne:नेपाल, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in S ...
, Sri Lanka,
Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-lar ...
,
Bangladesh Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mos ...
and
Burma Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...
. The closely related species, the clouded monitor, occurs in southern
Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...
,
Vietnam Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...
,
Cambodia Cambodia (; also Kampuchea ; km, កម្ពុជា, UNGEGN: ), officially the Kingdom of Cambodia, is a country located in the southern portion of the Indochinese Peninsula in Southeast Asia, spanning an area of , bordered by Thailan ...
,
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
,
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
, Sumatra,
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
and the Sunda Islands. They have not been confirmed on Sumatra, and have been found to be absent from the Andaman Islands. The species is mainly distributed through lower elevations below an altitude of 1500 metres, and is found both in dry semiarid desert habitats to moist forest. They are often found in agricultural areas.


Ecology and behaviour

Bengal monitors are usually solitary and usually found on the ground, although the young are often seen on trees. Clouded monitors by contrast have a greater propensity for tree climbing. Bengal and yellow monitors are sympatric but are partially separated by their habitat as Bengal monitors prefers forest over agricultural areas.Ghimire, H. R., & Shah, K. B. (2014). Status and habitat ecology of the Yellow Monitor, Varanus flavescens, in the Southeastern part of Kanchanpur District, Nepal. Herpetological Conservation and Biology, 9(2), 387-393. http://www.herpconbio.org/Volume_9/Issue_2/Ghimire_Shah_2014.pdf Bengal monitors shelter in burrows they dig or crevices in rocks and buildings, whilst clouded monitors prefer tree hollows. Both species will make use of abandoned termite mounds. Bengal monitors are diurnal like other monitors, becoming active around 6 AM and bask in the morning sun. During winter in the colder parts of their range, they may take shelter and go through a period of reduced metabolic activity. They are not territorial, and may change their range seasonally in response to food availability. They are usually shy and avoid humans. They have keen eyesight and can detect human movement nearly 250 m away. When caught, a few individuals may bite, but rarely do so. Although they are found on agricultural land, they prefer forests with large trees. Generally, high ground cover with large trees are favorable areas. Captives have been known to live for nearly 22 years. Predators of adults include pythons, mammalian predators and birds. A number of ectoparasites and endoparasites are recorded.


Breeding

Females may be able to retain sperm, and females held in confinement have been able to lay fertile eggs. Some species of monitor lizards such as the
Nile monitor The Nile monitor (''Varanus niloticus'') is a large member of the monitor family (Varanidae) found throughout most of Sub-Saharan Africa and along the Nile, with invasive populations in North America. The population in West African forests and ...
have additionally demonstrated to be capable of
parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...
. The main breeding season is June to September, but males begin to show combat behaviour by April. Females dig a nest hole in level ground or a vertical bank and lay the eggs inside, filling it up and using their snouts to compact the soil. The females often dig false nests nearby and shovel soil around the area. They sometimes make use of a termite mound to nest. A single clutch of about 20 eggs are laid. The eggs hatch in 168 to nearly as long as 254 days. About 40-80% of the eggs may hatch.


Locomotion

They are capable of rapid movement on the ground. Small individuals may climb trees to escape, but larger ones prefer to escape on the ground. They can climb well. On the ground, they sometimes stand on the hind legs to get a better view or when males fight other males. They can also swim well and can stay submerged for at least 17 minutes. They can use both trees and bushes for shelter.


Feeding

Bengal monitors tend to remain active the whole day. Large adults may ascend vertical tree trunks, where they sometimes stalk and capture roosting bats. The species is a generalist, and feeds on a varied diet of invertebrates and vertebrates. Invertebrate prey mostly consists of beetles and their larvae followed by orthopterans, but also maggots, caterpillars, centipedes, scorpions, crabs, crayfish, snails, termites, ants, and earwigs. Larger individuals in addition to invertebrates also eat a large amount of vertebrate prey, including toads and frogs and their eggs, fish, lizards, snakes, rats, squirrels, hares, musk shrews, and birds. Hares and rodents such as Indian bandicoot rats are often caught by digging them out of their nests. Diet may differ based on season and locality, for example, they often forage for fish and aquatic insects in streams during the summer, and individuals in Andhra Pradesh eat mostly frogs and toads. Bengal monitors will also scavenge carrion, and sometimes congregate when feeding on large carcasses such as that of deer. In areas where livestock are common, they often seek out dung to forage for beetles and other insects.


In culture

The lizard is known as ''bis-cobra'' in western India, ''Goyra'' in
Rajasthan Rajasthan (; lit. 'Land of Kings') is a state in northern India. It covers or 10.4 per cent of India's total geographical area. It is the largest Indian state by area and the seventh largest by population. It is on India's northwestern s ...
, or in
Bangladesh Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mos ...
and
West Bengal West Bengal (, Bengali: ''Poshchim Bongo'', , abbr. WB) is a state in the eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabitants within an area of . West Bengal is the fou ...
, ''goh'' in
Punjab Punjab (; Punjabi: پنجاب ; ਪੰਜਾਬ ; ; also romanised as ''Panjāb'' or ''Panj-Āb'') is a geopolitical, cultural, and historical region in South Asia, specifically in the northern part of the Indian subcontinent, comprising a ...
and
Bihar Bihar (; ) is a state in eastern India. It is the 2nd largest state by population in 2019, 12th largest by area of , and 14th largest by GDP in 2021. Bihar borders Uttar Pradesh to its west, Nepal to the north, the northern part of West ...
, as ''ghorpad'' in Maharashtra and as ''Thalagoya'' in Sri Lanka. Folk mythology across the region includes the idea that these lizards, though actually harmless, are venomous, and in Rajasthan, the locals believe that the lizards become venomous only during the rainy season.Auffenberg (1994):58 Monitor lizards are hunted, and their body fat, extracted by boiling, is used in a wide range of folk remedies. In Sri Lanka, the water monitor (Kabaragoya) is considered venomous and dangerous when confronted, while the Bengal monitor (Thalagoya) is considered harmless and rather defenseless. Land monitor meat is considered edible (especially by indigenous Veddah and Rodiya people) while water monitor meat is not. Killing a land monitor is usually considered a cowardly act, and is frequently referred to folklore along with other harmless reptiles such as
rat snakes Rat snakes are members – along with kingsnakes, milk snakes, vine snakes and indigo snakes – of the subfamily Colubrinae of the family Colubridae. They are medium to large constrictors and are found throughout much of the Northern Hemi ...
(Garandiya). A clan in Maharashtra called ''Ghorpade'' claims that the name is derived from a legendary founder
Tanaji Malusare Tanaji Malusare was a warrior and commander of Chatrapati Shivaji Maharaj. A local poet Tulsidas, wrote a powada describing Tanaji's heroics and sacrifice of life in the Battle of Sinhagad, which has since made him a popular figure in Indian f ...
who supposedly scaled a fort wall using a monitor lizard tied to a rope. The Bengal monitor's belly skin has traditionally been used in making the drum head for the '' kanjira'' (known as ''Dimadi'' in Maharashtra), a South Indian percussion instrument.


Conservation

While it is assessed LC (Least Concern) by the IUCN 2009, the assessment currently requires updating. The Bengal monitor is listed as Appendix I of
CITES CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...
and Schedule I of the 1972 Wildlife Protection Act. The wild population is decreasing as it is hunted for both consumption and medicinal purposes as well as for the skin. As it is adaptable to a range of habitats, the threat of habitat degradation is relatively less prominent and is superseded by the threat of
agricultural pollution Agricultural pollution refers to biotic material, biotic and abiotic byproducts of agriculture, farming practices that result in pollution, contamination or degradation of the environment and surrounding ecosystems, and/or cause injury to human ...
, as pesticides reduce the availability of prey. In Iran, it is also sometimes killed due to being seen as a dangerous threat.


Notes


References

* * * Auffenberg, W. 1979 Research on monitor lizards. Tiger Paper 6(4): 20–21. * Auffenberg, W. 1981 Combat behaviour in ''Varanus bengalensis''. J.Bombay N.H.S. 78(1):54-72. * Auffenberg, W. 1983 The burrows of ''Varanus bengalensis''. Rec. Zool. Surv. India 80:375-385. * Auffenberg, W. 1983 Courtship behaviour in ''Varanus bengalensis''. In Advances in Herpetology and Evolutionary Biology: Essays in Honor of Ernest E. Williams (Rhodin & Myata eds.): 535–551. * Auffenberg, W. 1983 Notes on feeding behaviour of ''Varanus bengalensis''. J. Bombay N.H.S. 80 (2): 286–302. * Auffenberg, W. 1986. The Indian monitor lizard. Sanctuary Asia. 6 (4):327-333. * Ghimire, H. R. & Shah, K. B. (2014). Status and habitat ecology of the Yellow Monitor, ''Varanus flavescens'', in the Southeastern part of Kanchanpur District, Nepal. Herpetological Conservation and Biology, 9(2), 387–393. http://www.herpconbio.org/Volume_9/Issue_2/Ghimire_Shah_2014.pdf * Mertens, R. 1942. Ein weiterer neuer Warane aus Australien. Zool. Anz. 137: 41-44


External links


The online Little Book of Monitor Lizards
{{Taxonbar, from=Q756805 Varanus Lizards of Asia Reptiles of India Reptiles of Nepal Reptiles of Sri Lanka Reptiles of Bangladesh Reptiles of Myanmar Reptiles of Laos Reptiles of Vietnam Reptiles of Cambodia Reptiles of Thailand Reptiles of Malaysia Reptiles of Brunei Reptiles of Indonesia Reptiles of Iran Reptiles described in 1802 Taxa named by François Marie Daudin Reptiles of Borneo