Taxonomic name: Varanus indicus (Daudin, 1802)
Synonyms: Monitor chlorostigma, Monitor doreanus, Monitor douarrha, Monitor indicus, Monitor kalabeck, Tupinambis indicus, Varanus chlorostigma, Varanus guttatus, Varanus indicus indicus, Varanus indicus kalabecki, Varanus indicus spinulosis, Varanus leucostigma, Varanus tsukamotoi
Common names: ambon lizard (English), erebachi (Marovo), flower lizard (English), George's island monitor, Indian monitor (English), Indian monitor lizard (English), kalabeck monitor, mangrove monitor (English), Pacific monitor (English), Pazifikwaran (German), regu (Roviana), sosi (Touo), stillahavsvaran (Swedish), varan des indes (French), varan des mangroves (French), varano de manglar (Spanish)
Organism type: reptile
Varanus indicus (mangrove monitor) is a terrestrial-arboreal monitor lizard that has been introduced to several locations for its meat, skin or as a biological control agent. It has created a nuisance on many islands preying on domesticated chickens and scavenging the eggs of endangered sea turtles. Bufo marinus (cane toad) was introduced to control mangrove monitor populations in several locations, but this has led to devastating consequences. In many places both of these species are now serious pests, with little potential for successful control.
Varanus indicus (mangrove monitor) is darkly coloured with small yellow spots. It has a long, narrow head attached to a long neck. It has four strong legs, each with five sharp claws. The tail of V. indicus is very strong and highly compressed. Large scales cover the face, giving it a glassy appearance, while the rest of the body has oval-shaped, keeled scales. (HJHS, undated). V. indicus can weigh between 500g and 1900g, while reaching lengths between 50cm and 200cm. Males are much larger than females. (Bennett, 1995) V. indicus has a dark drown iris with a golden ring around it. It has an exceptional ability to enlarge its mouth significantly by spreading its hyoid apparatus and dropping its lower jaw for large prey consumption. The mouth is outlined in red, a result of blood mixed with saliva, which may frighten predators or attract prey, similar to Komodo dragons. "The teeth are serrated along their anterior and posterior edges with the dentary teeth directed slightly laterally and the maxilliary teeth directed vertically." V. indicus has taste buds on the roof of the mouth and the tongue is frequently protruded, functioning as a chemical sensor. (HJHS, undated). V. indicus can live to be 15 years old. (Brook et al, 2004).
Varanus doreanus, Varanus indicus spinulosus
coastland, marine habitats, natural forests, riparian zones, wetlands
Varanus indicus (mangrove monitors) are tropical reptiles that can be found in mangroves, forests, swamps, and rainforests. They are most often found close to a water source. They prefer open areas to thick forests and have the capability to climb with great agility, dive, swim, and jump from high places. They have also been known to dig quite efficiently. In some areas they spend most of their time in the water, resting or looking for food. V. indicus may also take shelter in a tree, under a rock, in the hollow of a log or branch, or seldom in higher elevations and dry regions. In captivity they prey on fish but have no problem catching fish in deep water when not in captivity. (Bennett, 1995). Brook et al (2004) reports that V. indicus occupies/forages mainly around back swamps and paleochannels of floodplain. A male mangrove monitor has a home range of .4ha, while the female has a range of .9ha. (Bennett, 1995)
Varanus indicus (mangrove monitor) feeds on domesticated chickens and their eggs in many locations where it has been introduced. (Bennett, 1995). On Tetepare Island in the Western Province of the Solomon Islands, V. indicus is known to scavenge the nests of turtles, including the endangered leatherback sea turtle (see Dermochelys coriacea in IUCN Red List of Threatened Species) (Read & Mosby, 2006).
The skin of Varanus indicus (mangrove monitors) is used on ceremonial drums and as leather (Bennett, 1995). V. indicus was introduced to Micronesia during the Japanese occupation as a food source and for rat population control (Buden, 2000). V. indicus was popular in the international pet trade in the late 1970's and early 1980's. In 1980, 13,000 mangrove monitors were traded around the world (Bennett, 1995).
Varanus indicus (mangrove monitor) can have parasitic nematodes (round worms) on their body (Greer, 2006). They are very shy animals and are wary of humans when accustomed to human habitation. (HJHS, undated). In captivity, males are more aggressive than females. Instead of biting when threatened, V. indicus will defecate on an attacker. Nocturnal nesting has been reported for V. indicus while in captivity. (Greer, 2006). V. indicus is said to be a protected species in Indonesia. (Bennett, 1995).
Native range: Palau Islands (ITIS, 2006)
Known introduced range: Northern Australia, Solomon Islands, Ireland, Guam, Micronesia, Marshall Islands, Japan, Northern Mariana Islands, Timor-Leste, Indonesia, Guniea, New Guinea (Howarth, 1990; Buden, 2000; ITIS, 2006; EMBL, 2005; Brook et al, 2004; Read & Mosby, 2006; Bennett, 1995; Reed et al, 2000; Perryet al, 1998).
Introduction pathways to new locations
Biological control: Varanus indicus (mangrove monitor) was introduced to the island of Kosrae in Micronesia for ant control. (Howarth, 1990)
Natural dispersal: Varanus indicus (mangrove monitors) are excellent swimmers and visit islets near Guam's shore: populations on these islets are uncertain. (Perry et al, 1998).
Pet/aquarium trade: In 1980, 13,000 Varanus indicus (mangrove monitors) were traded around the world. (Bennett, 1995).
Biological: Varanus indicus (mangrove monitor) was introduced to the island of Kosrae in Micronesia for ant control. Populations grew significantly, and the country introduced Bufo marinus to regulate the burgeoning populations of V. indicus. Now both species exist on the island and are considered pests. (Howarth, 1990). A similar situation occured on the Marshall Islands as V. indicus was introduced prior to World War 2, probably for their skins, food and rat control. V. indicus began raiding chicken houses and their numbers increased drastically. Bufo marinus was introduced to regulate the lizard population. As populations of V. indicus dropped, the rat populations on the island rose. Bufo marinus was similarily introduced to Palau Island for mangrove monitor control. Lizard popluations declined on Palau but an increase was evident in the population of beetles known to be a major coconut pest. (Bennett, 1995)
Physical: V. indicus is seen as a threat to domesticated fowl and is trapped, poisoned, or killed near developed or agricultural areas. (HJHS, undated).
Varanus indicus (mangrove monitor) is a carnivorous, terrestrial-arboreal predator (Uetz, 1996) that primarily feeds on snails, carrion (rotting eggs), (Greer, 2006), piglets (Buden, 2000), frogs, lizards, crabs, fish, insects, birds and their eggs, and other reptilian eggs. (Brook et al, 2004). A study was conducted in Guam that provided a specific breakdown of V. indicus's diet over three years. The study found that V. indicus ate 45% arthropods, 27.2% scincid and gekkonid lizards and their eggs, 13.6% terrestrial crabs, 9.1% rats and 4.5% Brahminy blind snakes. HJHS (undated) reports that, in urban settings the diet of V. indicus consisted of domesticated chickens and their eggs, squid (from fishing bait) and aluminum butter wrappers. As an opportunistic feeder, V. indicus can change its prey class based on abundance or availability, allowing it to adapt to many habitats. (HJHS, undated).
Male Varanus indicus fight for females prior to courtship. (HJHS, undated). Males in combat are upright, in a grappling/dancing posture. (Uetz, 1996) Male V. indicus mount the females during copulation and orient themselves head to head with their mate. The pair then travel 360° in a slow rotation, the male remaining on top of the female. After copulation, male mangrove monitors will rub the dorsum of female monitor's head and forequarters with their chin. Female mangrove monitors are smaller than most varanids, and therefore yield a smaller clutch size, between 2-12 eggs. (HJHS, undated). When food is abundant, V. indicus may reproduce quickly, producing a large number of small clutches. (Brook et al, 2004). In New Guinea, recently hatched specimens have been collected every month of the year. (Bennett, 1995). Ovarian mass is greater during the dry season for females. Male mangrove monitors have testicular sperm all year round and their fat body mass does not differ between seasons, unlike females who have higher fat contents during the dry season, mainly for egg production. (HJHS, undated).
The eggs of Varanus indicus (mangrove monitors) are 3.5-5cm in length, oblong and white, and take approximately 7-8 months to hatch. No parental care is given to the young when they hatch. (HJHS, undated).
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Tuesday, 9 January 2007