Years later, it was classified as a subspecies of the closely related emerald tree monitor (V. prasinus), but a 1991 review of the complex returned V. beccarii to species status, based on its black colouration and keeled scales on the neck.

[6][7] Arguably, it should be maintained as a subspecies of the emerald tree monitor based on similarities in their hemipenial structures,[8] but genetic evidence supports their treatment as two different species.

[5][11] Hatchlings and juveniles of V. beccarii are a dark grey in colour, with regular rows of bright yellow-green dots which are particularly noticeable on their backs.

Fully grown specimens reach 90–120 cm (35–47 in) in overall length (including tail), with the males slightly larger than the females.

[12] In fact, the tail is used solely for this purpose, as the animal does not evince the defensive tail-lashing behaviour seen in other monitor species.

In the wild, the black tree monitor is reported to be nervous and high-strung; it will flee if threatened, and if handled carelessly, will bite, scratch, and defecate on the offender.

[14] The black tree monitor is primarily insectivorous, consuming mostly insects but also smaller lizards, small mammals such as shrews, scorpions, eggs, and the nestlings of birds.

Possible causes include substrate humidity being too high at least at the last third of the incubation period, nutritional deficits of minerals and vitamins experienced by the mother prior to laying, or an increased gestation period due to lack of suitable sites for laying thus causing thickened eggshells too difficult to be broken to hatch.

The study below suggests that the latter is likely not the case as eggshells were not particularly thick compared to the successfully hatched eggs of other tree monitors, and dead embryos had not yet begun attempting to perforate the shell.

By 161 days, all three embryos had fully developed, although only one survived, and only after it was forcibly hatched and taken out of the egg, after which it was further incubated with the yolk sac still intact.