Problem statement: Southeast Asian water monitor lizards (Varanidae) of the Varanus salvator complex are among the largest living lizards of the world. They are top predators in most environments they inhabit in insular Southeast Asia where large carnivorous mammals are missing. At the same time, water monitors are highly exploited for the international reptile leather trade. From Indonesia alone nearly 500,000 specimens are legally exported every year to Europe and the USA and the unreported figure may be much higher. This unsustainable harvest of water monitor lizard populations can lead to the extinction of locally restricted (endemic) species when the taxonomic distinctness of island populations is not recognized.

Methods: Traditionally, Southeast Asian water monitors were regarded as one widespread species with several subspecies. In order to demonstrate the taxonomic distinctness of various island populations, morphological features, such as specific scale counts, morphometric measures and colour pattern features, of numerous preserved voucher specimens from major European natural history collections were investigated. Advanced statistics were applied to the morphological data to separate and delimit distinct monitor species.

Outcomes and impact: The taxonomic investigations revealed that the widespread Southeast Asian water monitors represent a complex of at least seven distinct species. Several of the assumed subspecies are now considered species, and two hitherto unrecognized monitor lizard species were described as new to science. Each species inhabits a much smaller distribution range than Varanus salvator. Some are even restricted to single islands, such as the newly discovered Varanus palawanensis that is only found on Palawan and its smaller off-shore islets within the Philippine Archipelago.

Lessons: The discovery of new monitor lizard species such as the large-growing V. palawanensis clearly demonstrates the need for taxonomic expertise as currently not even the more conspicuous vertebrates on our planet are all known to us. The ability to distinguish CITES-relevant giant monitor lizard species can help to prevent their over-exploitation. Only recognition and protection of distinct species can ensure their persistence.