Monitor lizard
Large, intelligent lizards with venom and high metabolism.
Monitor lizards are lizards in the genus Varanus, the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, with one species also found as an invasive species in the southern United States. About 94 species are recognized, ranging in adult length from 20 cm (7.9 in) to over 3 m (10 ft) for the Komodo dragon, though the extinct megalania (Varanus priscus) may have reached lengths of more than 7 m (23 ft). Most species are terrestrial, but many are arboreal or semiaquatic, and while most are carnivorous, a few species eat fruit and vegetation.
- Scientific name
- Varanus
- Family
- Varanidae
- Native range
- Africa, Asia, Oceania
- Number of species
- About 94
- Adult length range
- 20 cm to over 3 m (extinct up to >7 m)
- Diet
- Mostly carnivorous; a few species frugivorous
- Notable species
- Komodo dragon, megalania (extinct)
Lore & Background
The generic name Varanus derives from the Arabic word waral, meaning 'lizard beast'. In English, they are called 'monitors' or 'monitor lizards', a name possibly suggested by their habit of standing on hind legs or warning of venomous animals, though these explanations postdate Linnaeus naming the Nile monitor Lacerta monitor in 1758. Linnaeus may have mistakenly connected the German Waran to warnen ('to warn') or the Greek ouranós ('sky'), leading him to Latinize it as monitor ('warner' or 'adviser'). In Austronesian languages, they are known as biawak, bayawak, or variations; in South Asia, as hangkok, ghorpad, uḍumbu, gohi, and many other names; in West Africa, as awọ́nríwọ́n, mbossé, or bar; in Australia, as 'goannas' due to confusion with iguanas; and in South African English, as leguaans or likkewaans from Dutch.
Reader's Guide
Monitor lizards are significant for their unique biological traits and ecological roles. They have the highest standard metabolic rates of all extant reptiles, enabled by a heart with a well-developed ventricular septum that separates pulmonary and systemic circuits during systole, allowing mammalian-equivalent pressure differentials. Most varanids are venomous, with venom glands in the lower jaw; their venom is diverse, including anticoagulant effects and, in some species like the Komodo dragon and desert monitor, neurotoxic effects. They are also notable for their intelligence: some species can count up to six, Nile monitors cooperate when foraging, and Komodo dragons recognize keepers and show distinct personalities. Their distribution spans Africa, Asia, and Oceania, with fossil evidence in Neogene Europe. As oviparous animals laying 7 to 38 eggs, some species like the Komodo dragon can reproduce via parthenogenesis. Their morphological conservatism despite a vast size range makes them unique among animals.
Did You Know?
- Monitor lizards have the highest standard metabolic rates of all extant reptiles.
- Most varanids are venomous, with venom glands in their lower jaw; some species have neurotoxic venom.
- Some monitor species can count up to six, as shown in studies with rock monitors and snails.
- The extinct megalania (Varanus priscus) may have reached lengths of more than 7 m (23 ft).
More in Extant Reptiles & Amphibians 1-22
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