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The Crocodile Monitor Lizard – Reality and Legend

Despite – or perhaps because of – its immense size, impressive armament of teeth and scarcity, the spectacular Crocodile Monitor Lizard (Varanus salvadorii) is often considered the crown jewel of private and public monitor collections.

I became acquainted with these formidable giants when they were first imported into the USA, and have cared for several at the Bronx and Staten Island Zoos.  Their husbandry is straightforward, but little is known about their lives in the wild.  Today I would like to summarize what we do know; please see the article referenced below for notes on captive care.


Crocodile MonitorCrocodile Monitors approach 9 feet in length – nearly as long as the famed Komodo Dragon, but less stoutly built.  There are recurring but unverified reports of much longer individuals.

The Crocodile Monitor’s prehensile tail often exceeds 5 feet in length.  The body is dark gray to black in color and marked with yellow spots, making for quite a spectacular appearance.  The snout area, especially in mature males, is large and bulbous.

Crocodile Monitors are unusually large for canopy dwelling lizards…the 3 foot long black tree monitor is far more typical.  However, aided by slender bodies, long claws and prehensile tails, they are very agile climbers.

Their teeth are unique among monitors, being serrated and over-lapping – possibly an adaptation for carrying large prey high above the forest floor.

Range and Habitat

Crocodile Monitors are found only in southern New Guinea.  Highly arboreal, they seem restricted to the canopies of mangrove swamps and lowland forests along rivers.


Little studied due to the inaccessibility of their habitat, the Crocodile Monitor’s limited range renders it a conservation concern.  Listed on CITES Appendix II.


Females lay 6-12 eggs at a time, and up to 3 clutches per year in captivity (multiple clutches may be a function of food availability), with arboreal nest sites being favored.  In common with other tree-dwelling monitors, they likely deposit eggs in tree hollows and similar sites above ground in the wild.


Their natural diet has been little studied, but probably includes nearly any animal that can be overpowered.  Likely candidates would be cuscus, tree kangaroos, naked-tailed rats, bandicoots, possums, bats, birds, frogs, snakes, lizards, invertebrates and carrion.

An Undiscovered Giant in New Guinea?

Long a creature of legend, the Crocodile Monitor is the source of rumors alleging “Papuan Dragons” of 20 feet in length.  This specie’s habitat is inaccessible and barely explored….I like to believe that it or an as yet un-described monitor may indeed reach such lengths.

A Calculating Reptile

Like all Varanids, Crocodile Monitors are highly intelligent.  One huge adult that escaped its enclosure at the Bronx Zoo wedged himself behind a cage while attempting to hide from myself and a co-worker.  As we moved into position to flush him, he very deliberately peered around first one and then the other side of his hideout, trying to keep us both in sight.  When we backed off, he followed our progress, again changing position periodically to ascertain where we were.

The lizard remained stationary while we were near, and only ran when we gave him some space.  When he did move, the old fellow made unerringly for a more secure retreat that he had obviously “decided upon” while in hiding.

Further Reading

Please see my article Monitor Lizards: an Overview for information about the captive care of this and related species.

A comprehensive field report on the crocodile monitor’s habitat is posted here.


Crocodile Monitor image referenced from wikipedia and originally posted by Ltshears

The Monitor Lizards (Family Varanidae) – Family Overview and Species Accounts, Part II

Click here: The Monitor Lizards (Family Varanidae) – Family Overview and Species Accounts, Part I, to read the first part of this article.

Monitor Intelligence
Monitor lizards exhibit an extraordinary degree of intelligence and retain what they have learned for long periods.  Gould’s monitors (V. gouldii) have been observed taking indirect routes when chasing rabbits.   Rather than running directly after the rabbit, they veer off in a direction that takes them away from the animal, but leaves the lizard in a position to intercept the rabbit at the mouth of its burrow!

Parentie monitors (V. giganteus) seeking animals hidden within burrows do not dig away at the burrow entrance (as would a foolish dog!) but rather sniff the ground several feet away.  Once they locate the underground position of their prey, they dig directly down to reach it, keeping an eye on the entrance as well.

An Experience with a Bright Monitor
I have often had the good fortune to observe monitor intelligence in action.  While working at the Bronx Zoo, I once looked up from a phone conversation to see a 6 foot long crocodile monitor (V. salvadorii) go shooting by, followed by an equally fast-moving coworker of mine.  We cornered the animal behind a large cage, where he remained as long as we were in view.  As soon as we moved off to either side, he cautiously peered around the cage and looked both right and left, to fix our new positions.  The lizard most definitely did not want either of us sneaking up on him, and made sure he saw both of us at all times.

Mangrove MonitorThe stout fellow was recaptured – with more wear and tear to us than he!  Monitors are incredibly strong – a 7 foot long water monitor (V. salvator) I worked with was able to move along with myself and 2 other strong men trying to pin him down – this despite being rather seriously ill.

Monitor Venom
In 2005, Dr. Bryan Frye and researchers at Australia’s Melbourne University discovered that several species of monitor lizards, including the Komodo dragon, V. komodoensis and the lace monitor V. varius, produce venoms of varying strengths.  Lace monitor venom was subsequently shown to cause the lizard’s prey to rapidly loss consciousness by affecting the blood’s pressure and clotting ability.

Until this discovery, bacteria in the mouth of the Komodo dragon were thought to be responsible for the quick onset of death seen in deer, goats and other large animals bitten by these lizards.  While such bacteria no doubt add to the trauma associated with a bite, it now seems certain that venom delivers the knockout blow.  A combination of venom and bacterial infection is also the likely source of the strong reaction often associated with bites inflicted by monitor lizards upon people.

The Bearded Dragon, Pagona vitticeps, a popular pet species not related to the monitor lizards, was also shown to produce mild venom – other members of the lizard family Agamidae are being studied.

An interesting article on Florida’s introduced Nile monitor lizards is posted at:

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