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As their common name suggests, water monitors are a semi-aquatic lineage, prefering lowland to mid-elevation riparian habitats.
Varanus nuchalis is a member of the sub-genus Soterosaurus (Ziegler and Bӧhme, 1997), which is comprised of the V. salvator Species Complex and V. rudicollis. This taxon was elevated to species status by Koch et al. (2007). This species is thought to occur in two color forms in its range, one being highly melanistic and lacking discernable dorsal patterning. The lighter form, present throughout most of the species' distribution, has a dark gray to black ground color; head predominately dark, overlain with occasional small white spots; nuchal scales with light posterior margins and light medial stripe, occasionally; trunk with variable number of transverse bands of white oscelli, variable white speckling, and regularly with a light paravertebral stripe; limbs gray to black, with minimal yellow-white speckling; tail with whitish mottling proximally, becoming banded distally. Ventral coloration cream to white, with dark transverse bands on snout, and dark-chevron shaped gular bands; trunk often with dark reticulate pattern; limbs cream, with minimal dark speckling; tail with dark reticulations proximally, becoming solid gray-black distally.
Varanus nuchalis is fairly common throughout its range, despite being threatened by collection for skin and pet trades, as well as for bush meat. Further study is required to determine the independent status of light and melanistic forms, in order to fully realize each form's conservation needs.
Varanus nuchalisis designated as a CITES Appendix II species. This taxon is not currently threatened by extinction, but may become so unless trade or other factors are closely monitored.
Varanus nuchalis is a relatively small member of the V. salvator Species Complex, characterized by by enlarged nuchal scales and often a light paravertebral stripe. Ventrally, this species is characterized by chevron-shaped transvese gular bands and the reticulate pattern of the trunk and proximal protions of the tail.
Varanus nuchalis can be distinguished from all non-Soterosaur Varanus species by characteristics of reproductive morphology (See Ziegler and Bӧhme, 1997). This species can be distinguished from all other members of the V. salvator Species Complex and V. rudicollis by combinations of: (1) enlarged nuchal scales; (2) low numbers of dorsal scales; (3) narial opening at one-third distance from tip of snout to ocular; (4) low numbers of scales around tail at one-third distance from base; (5) high numbers of midbody scales; (6) high numbers of ventral scales; (7) occasional longitudinal stripe medially in nuchal region, paravertebrally on trunk; and (8) general reduction in oscelli size comprising dorsal bands (except directly adjacent to vertebral column; Koch et al., 2007)
Varanus nuchalis has been documented throughout the Greater Visayan Faunal Region, with the typical form occuring on the islands of Negros, Panay, and Cebu. The melanistic form of this species has been documented on the islands of Masbate and Ticao.
As with many species of monitor lizards, Varanus nuchalis is an opportunistic feeder, and will seek out various sources of carion, as well as consuming small reptiles, amphibians, rodents, fish, and both terrestrial and aquatic arthropods.
The specific epithet was likely chosen in referrence to the enlarged, diagnostic nuchal scales exhibited by this species.
Visayan (Central) Pleistocene Aggregate Island Complex
Varanus nuchalis like all water monitors, is often found in disturbed to primary growth riparian habitats in low- to mid-elevations.
Varanus nuchalis most closely resembles other Philippine members of the V. salvator Species Complex, but is readly distinguished by its enlarged nuchal scales.
Varanus nuchalis, like all water monitors, is rather successful in moderately disturbed habitat, so long as some in-tact riparian habitat remains and populations are not overly stressed by harvest.
The most severe threats to Varanus nuchalis are likely from unsustainable harvest (for trade and bush meat) and habitat loss.
