The 'mangrove monitor' (Varanus indicus) had historically been considered a very wide-spread species showing extensive geographical variation. In 1999, Philipp, Böhme & Ziegler redefined the species with the designation of a neotype. Varanus indicus is thus distinguished by a dark brown to blackish background color covered with numerous small whitish to yellow spots typically less that 5 scales in size, the absence of a postocular stripe, an unpatterned throat, and a solid dark purple tongue, as well as other morphological differences (i.e. genital structure or scalation).
Varanus indicus occurs throughout the Moluccan Islands, possibly in Sulawesi (Böhme, Horn & Ziegler 1994, though this has been disputed), Timor, the Aru Islands, the Kei (Kai) Islands, New Guinea and its surrounding islands, the Bismarck Archipelago, the Solomon Islands, coastal portions of northern Australia (the Northern Territory and Queensland, absent from territory in between along the southern rim of the Gulf of Carpentaria), and (due to human introduction) in Micronesia. The neotype designated by Philipp, Böhme & Ziegler originated from Ambon in the Moluccas, also inhabited by the related Varanus cerambonensis. As the taxonomy of the indicus-complex remains to be resolved, it is likely that forms from many parts of this extensive range will eventually be given distinct taxonomic status.
Background color: Dark brown to blackish
Dorsal pattern: White to yellowish small (typically one to three but up to five scales in size) spots, arranged irregularly
Tail pattern: Anterior third spotted as on the dorsal surface; posterior two-thirds banded (blue pigmentation absent)
Throat/ventral pattern: Underside light-colored (white to yellowish); throat unpatterned; ventral surface indistinctly banded
Post-ocular stripe: Absent
Tongue color: Dark (purplish)
Despite the redefinition of indicus, the taxonomy of this species-complex is far from settled. Many 'mangrove monitor' forms exist from different localities whose true taxonomy is yet to be settled. These animals (Varanus c.f. indicus) commonly turn up the the reptile market labeled generically as 'mangrove monitors'.
Sprackland (2004) gave the following geographical variation:
It should be noted that this is only a basic characterization of some geographical variants. Differences within these populations themselves may exist and numerous different color forms continue to be discovered as well.
Photo courtesy of Jody Pieper. Note: The mangrove monitors from the Aru Islands were originally described as a distinct subspecies, Varanus indicus rouxi (Mertens 1926), a name which is now considered a junior synonym of Varanus indicus.
The Solomon Islands have been a large source of mangrove monitors seen in the pet trade. Specimens from these islands are often highly patterned wioth considerable dorsal spotting and a well-banded tail. Their appearance does not align with the redefinition of Varanus indicus as given by Philipp et al (1999) and so with future research should prove to be taxonomically distinct. Other phenotypes possessing reduced pattern are known from the Solomons, though the considerable degree of ontogenetic changes seen in indicus-complex pattern may explain these.
Photo courtesy of Kenneth Jensen. Note: this specimen possesses a pink tongue, a feature distinguishing it from Varanus indicus sensu stricto.
Mangrove monitors are present in the Mariana Islands, though it is widely accepted that their presence here is due to human - most likely recent - introduction (Cota 2008). The population on Saipan was once described as a distinct species (Varanus tsukamotoi Kashida 1929), though this form is no longer recognized.Locality: Saipan.
Photos courtesy of Jody Pieper. Note: The above two specimens certainly do not correspond to Varanus indicus as now defined. They are similar in pattern to the Varanus c.f. finschi discussed separately, with which they occur on the same islands. The two do differ in other respects, such as the yellow (vs. white) underside of these animals.
Böhme, W.; Horn, H. & T. Ziegler (1994): On the taxonomy of the Pacific monitor lizards (Varanus indicus complex): Resurrection of Varanus doreanus (A.B. MEYER, 1874) and description of a new subspecies. Salamandra 30 (2): 119-142.
Cota, M. (2008): Varanus indicus and its presence on the Mariana Islands: natural geographic distribution vs. introduction. Biawak 2 (1): 18-27. (http://www.varanidae.org/Vol_2_No_1.pdf)
Kishida, K. 1929. A new Monitor from the island of Saipan, South Sea Islands. Lansania. 1(1): 13-16.
Mertens, R. (1926): Uber die Rassen einiger indo – australischer Reptilien. Senckenbergiana 8: 272-279.
Philipp, K. M.; Böhme, W. & T. Ziegler (1999): The identity of Varanus indicus: Redefinition and description of a sibling species coexisting at the type locality (Sauria: Varanidae: Varanus indicus group). Spixiana 22 (3): 273-287.
Sprackland, R. G. (2004): Evolution, Systematics, and Variation of Pacific Mangrove Monitor Lizards. Lizard Biology 2 (1): art. 1 (http://www.curator.org/legacyvmnh/VMNH_Publications/MuseumJournals/Lizard%20Biology/new_page_2.htm)