Dumeril's Monitor

Dumeril's Monitor Lizard (Varanus dumerilii)

First published in Reptilian Magazine

Dumeril's monitor is a large lizard from southeast Asia about which very little is known. Until a few years ago they were not uncommon in the pet trade in Europe and the U.S.A. but breeding success with the species was very limited and today they rarely appear on dealers' lists. Dumeril's monitor is completely protected in parts of its range, but nobody  knows if the species is really very rare or just extremely secretive. The impression given of this animal from the literature is of a large, heavily built lizard which shelters in trees and forages for crabs and other invertebrates in swamps and on seashores. Nothing is known of their breeding habits, but the eggs hatch to reveal flourescent-orange youngsters, which may spend most of their time buried in soft earth until they develop the much more inconspicuous colouration and pattern of the adults. There are very few published observations of this lizard in the wild; almost all of them date from more than 50 years ago and it is often difficult to be certain whether the lizards concerned really are Dumeril's monitors, because the species is often confused with others, even today. The purpose of this article is to summarize what is known about this mysterious creature both in the wild and in captivity.

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Varanus dumerilii
Varanus dumerilii shares its range with three other large lizards, all of which belong to the genus Varanus; the Asiatic water monitor (V.salvator), the Bengal monitor (V.bengalensis) and the enigmatic rough-necked monitor lizard (V.rudicollis -see my review of this species in Reptilian volume 1 number 9). Whilst water monitors and Bengal monitors are found in a wide range of habitats including human settlements, and are of great economic importance for their skins and flesh, both Dumeril's and the rough-necked monitors shun sites of human habitation and seem to frequent only undisturbed mangroves and forests. Their is no trade in their leather and the flesh of both species has an undeserved reputation for being poisonous. Outside the pet trade (where they fetch around ** - an albino specimen was recently offered for sale in the U.S.A. for $9000) they have no economic value. The fact that there have been so few sightings of such large animals suggests that they are very rare, and it seems certain that they have already been exterminated from a large part of their previous range and survive only in dwindling patches of undisturbed habitat. Very few attempts have been made to study these lizard in the wild and many of them (including my own) have been completely unsuccessful. Forest monitors are of great ecological importance because they are large carnivores with very few natural predators. Despite their size and their ability to swallow large prey items whole, most of their food consists of invertebrates, which they consume in enormous numbers. An understanding of their way of life is vital if they, and the forests they live in, are to be properly conserved.

Taxonomy

Varanus dumerilii was first described by Schlegel in 1839. In 1912 specimens from northern Borneo with unsusual scalation were described by Boulenger as V.heteropholis, later made the subspecies V.dumerilii heteropholis by Mertens 1942. The validity of this taxonomy has been questioned by Brandenberg (1983) and Sprackland (in press), and here they are treated as a single race.

Distribution

Location data are given in the appendix. Dumeril's monitor is known from southern Burma and Thailand ("south of the Isthmus of Kra" (Lekagul 1969)), peninsular Malaysia, Borneo, Sumatra and many smaller islands. They were recorded on Singapore early this century (, but are are certainly exinct there now. In Myanmar (then Burma) they were noted specially on the Mergui Archipelago and adjacent mainland and said to be plentiful on Kau-ye Kyun  island (formerly Sir Charles Forbes' Island - 11oN, 98.5oE) (Smith 1930). NUTPHAND (no date) claimed they were "frequently" found in the southern forests of Thailand, and occasionally found in the west around Kanchanaburi province. Lekagul (1969) considered it to be commoner than V.rudicollis in the dense jungle south of the Isthmus of Kra.

Morphology

Maximum size claimed in the literature is 150cm (Sprackland 1976) but no specimens over 130cm seem to have been recorded in the wild. Healthy adult males maintained in captivity may weigh 3kg, females of 1m long (they may no grow larger than this) may weigh 2.3kg. Weights of wild animals may be lower than this. Hatchlings weigh around 17g and have body length of about 8cm (Radford and Paine 1989). After six months they may have grown to almost 30cm total length.Details of morphology and scalation can be found in (De Rooij 1915; Mertens 1942; Taylor 19**; Brandenberg 1983; Sprackland in press). Krebs (1979) reported that Dumeril's monitors are able to seal their nostrils when submerged, an adaptation that may be shared with other aquatic monitor lizards. Dumeril's monitor is often confused with the rough-necked monitor, e.g. Coburn's (1987) photograph of "V.rudicollis" is really V.dumerilii. The species can be distinguished mainly from the scales on the back of the neck, which are enlarged in both species, but raised and spiny in V.rudicollis and more or less flat in V.dumerilii.

Diet

The stomach contents of only four animals have been examined (Losos & Greene 19** & Brandenberg 1983); all contained crabs and one also contained a spider and an insect larva. Loveridge's (1962) claim that they eat birds needs verification. Raven (1946) records that they feed on the eggs of green turtles and Barbour (1921) that they eat ants. The ability of this lizard to feedon crabs is well documented in the literature. Krebs (1977) considered them to be specialised crab eaters, levering off the larger appendages, puncuring the shells with the needle-sharp, sparsely arranged teeth and swallowing them whole. Where crabs are absent the bulk of the diet may consist of insects collected on the forest floor (Auffenberg 19**).

Behaviour

The most intriging aspect of the biology of Dumeril's monitor lizard is the extraordinary colouration and pattern of the hatchlings which fades within weeks and changes to drab adult colouration within two months (first reported in Horn & Schulz 1977). More than one person has noticed the resemblance of the young lizards to hatchling king cobras. The pattern certainly looks like a mimic of a venomous or unpalatable animal and it is difficult to see how such colouration could serve as camouflage. Such talk is entirely speculative, because there have been no observations made on hatchlings in the wild. In captivity hatchlings may bury themselves or remain on branches above the ground. Both young and adult Dumeril's monitors are superb climbers and swimmers. Krebs (1979) reports that they can climb slippery telgraph poles with ease. According to Nutpand (no date) they are less active than other monitor species, spending most of their time sleeping in rock crevices and tree hollows. He suggests that they may habitually return to the same retreat after foraging. Smith (1930) records that they run into the sea to escape from dogs. Davis and Darling (1986) report ritual fighting between Dumeril's monitors in the manner typical for large varanids; opponents grip each other shoulders with the forefeet whilst standing bipedally using their tails as supports and attempt to push each other over. This behaviour is generally held to occur between male monitor lizards, but problems of sex identification make this an uncertain claim. Patterns of acivity in the wild are unknown. Sprackland (1976) reports that captives have two daily peaks of activity in mid morning and late afternoon. According to Radford and Paine (1989) captives in north America become less active from mid August until the end of September

Care in Captivity

In captivity this species should be provided with a very large enclosure that allowsthem to climb, dig and at lewast emerse themselves in water. Thermoregulatory behaviour of this species has not been studied, but many monitor lizards like to bask at tempetaures in excess of **oC and hot spots should be provided accordingly. There is some suggestion that the thermal preferences of the sexes may differ. There appears to be no sexual diamorphism, but males may recah a greater length and mass than females. A method of sexing Dumeril's monitors that involves the use of anaesthetics and fiberoptic laparoscopy is given by Davis and Phillips (1991). The only published report of breeding is Radford and Paine (1989). A pair housed apart in 150 X 130 X 270cm enclosures were fed on rodents, horsemeat, fish and dog "chow" with vitamin and mineral supplements were introduced to each other every August for six years. In the sixth year copulation occurred over three days and five weeks later 14 eggs were laid over eight days, of which five proved fertile. They were incubated at 26.7-30oC and hatched after 215-222 days. The hatchlings grew well on a diet of worms, crickets, catfood and parts of baby mice. Zimmerman (1986) gives an incubation time of 203-215 days at 28oC for eggs that were also laid in September.

According to Nutphand (no date) Dumeril's monitor is known as hao-chang-kao (white jungle monitor) in southern Thailand. In Malaysia it is sometimes known as biawak kudong (Harrison and Lim 1957).

APPENDIX.  LOCATION DATA FOR VARANUS DUMERILII

Kuala Teku, Peninsular Malaysia.     SMITH 1922.
Mergui Archipelago and coast of Mergui      SMITH 1930
Khao Chong, Trang.      TAYLOR
Kedah, Mallaka    SCORTECCI 1929
Tavoy SMITH 1932
Banjermasin    SCHLEGEL 1839
Batu MULLER & SCHLEGEL 1845
Mergui   BLYTHE 1853
Singawang   BLEEKER 1858
Deli, Sumatra    BOULENGER 1890
Indragiri, Sumatra. SCHENKEL 1901
Tenesserim ANNANDALE 1905.
Nanag Raoen, Fluss Howong    VAN LIDTH DE JEUDE 1905
Taluk, Sumatra     DE LAANG & DE ROOIJ 1905.
Bangka    BLEEKER 1860
Solok   MULLER 1887
Pulu Gallang, Rhiau Archipelago    CHASEN & SMEDLEY 1927
Borgon, Baram, Sangasanga, Lahat, Balikpanan Borneo; Sibolga, Bama Sumatra      SPRACKLAND 19**
Singapore   FEJERVARY 1935
Stabat Sumatra   BOETTGER 1893
Serdand, Talu, Baram, Kuching, Pangkalan, Ampat, Buntal, Mt Dulit, Rejank River, Akar River, Bogon, Howong River, Tandjong,  DE ROOIJ 1915.
Sampit, Borneo;  Banatng Kwis, Sumatra; Sungei Rampah, Sumatra; MERTENS 1942.
Rawang, Selangor; Penang Hill, below Belercteiro; Kota Tinggi, Johor, Malaysia         BENNETT (in prep)
Specimens examined from Sumatra (Deli, "east coast", Taloek, Serdang, Bangka, and Batoe) and Borneo (Balikpapan, Banjermasin and Nanga Raoen) (BRANDENBURG 1983).

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