Bengal monitor
The Bengal monitor or common Indian monitor, is a monitor lizard found widely distributed over the Indian Subcontinent, as well as parts of Southeast Asia and West Asia. This large lizard is mainly terrestrial, and its length can range from about 61 to 175 cm from the tip of the snout to the end of the tail. Young monitors may be more arboreal, but adults mainly hunt on the ground, preying mainly on arthropods, but also taking small terrestrial vertebrates, ground birds, eggs and fish. Although large monitors have few predators 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 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 were once considered subspecies of the Bengal monitor, but now considered two species within the V. bengalensis species complex. What was once the nominate subspecies, V. bengalensis, is found west of Myanmar, while V. nebulosus is found to the east. V. nebulosus 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.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. 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. Hatchlings of V. nebulosus by comparison tend to have a series of backward-pointing, V-shaped bands on their necks.
Bengal monitors have external nostril openings 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 varanids, Bengal monitors have a forked tongue that is protruded in the manner of 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 greater rates of gas exchange and allows a faster metabolic rate and higher activity levels. Like all varanids, 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. 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. Their mandibular glands produce secretions at the base of the teeth, and although some varanids have been shown to have a venom, no toxicity has been reported in the Bengal monitor.
Distribution and habitat
The species ranges from Iran to Java, among the most widely distributed of varanid lizards as they are eurytopic and adaptable to a range of habitats. It is found in river valleys in eastern Iran, Afghanistan, India, Nepal, Sri Lanka, Pakistan, Bangladesh and Burma. The closely related species Varanus nebulosus, the clouded monitor, occurs in southern Burma, Vietnam, Cambodia, Thailand, Malaysia, Sumatra, Java 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 distributed mainly in the lower elevations, and is found both in dry semiarid desert habitats to moist forest. They are often found in agricultural areas, and are mainly found below 1500m altitude.
Ecology and behaviour
Bengal monitors are usually solitary and usually found on the ground, although the young are often seen on trees. V. nebulosus has a greater propensity for tree climbing. The two sympatric species Bengal and yellow monitor partially separated their habitat as Bengal monitor prefers forest over agricultural areas. Bengal monitors shelter in burrows they dig or crevices in rocks and buildings, whilst clouded monitors prefer tree hollows. Both races will make use of abandoned termite mounds. Bengal monitors, like other varanids, show true sleep at night and are diurnal, becoming active around 6 AM and bask in the morning sun. During winter, in the colder parts of their distribution 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 Varanus niloticus have additionally demonstrated to be capable of parthenogenesis. 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, guishaap or goshaap in West Bengal and Bangladesh, goh in Punjab and Bihar, 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. 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 is considered venomous and dangerous when confronted, while the Bengal monitor is considered harmless and rather defenseless. Land monitor meat is considered edible 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.
A clan in Maharashtra called Ghorpade claims that the name is derived from a legendary founder Maratha Koli leader Tanaji Malusare who climbed a fort using a monitor lizard and a rope. Folk traditions have various stories of monitor lizards being used by soldiers to climb walls of forts.
The Bengal monitor's belly skin has traditionally been used in making the drum head for the kanjira, a South Indian percussion instrument.