Description
The Bengal monitor has been said to reach nearly 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 and obese captives even more and the males grow to greater weight. The populations of India and Sri Lanka differ in the scalation from those of Myanmar, and these were once considered two species, but now considered two subspecies. The nominate subspecies is found west of Myanmar, while nebulosus is found to the east. The subspecies nebulosus is diagnosed 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 (Pakistan) 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. Hatchlings of nebulosus 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 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 (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. 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.
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