Trimeresurus sumatranus is a large heavy-bodied pitviper, with a prehensile tail. Adults may attain 1.6 metres (5 feet 3 inches) SVL (snout–vent length), with fangs over 10 mm (⅜ inch) long.
It is an arboreal species that is pale green in color with a red tail. The dorsal scales are edged with black, which may form crossbands in more mature specimens. There is a white or yellow stripe on each side along the first row of dorsal scales. Ventrally it is greenish or yellowish, and the ventral scales may be thinly edged with black.
Scalation includes 21 (23) rows of dorsal scales at midbody, 183–190/182–191 ventral scales in males/females, 57–66/55–64 subcaudal scales in males/females, and 8–10 supralabial scales.
In Borneo it inhabits lowland forests at elevations below 800 meters (2,600 feet).
Found in southern Thailand, West and East Malaysia (Sabah and Sarawak on Borneo) and Indonesia (Bangka, Billiton, Borneo, Sumatra and the nearby islands of Simalur, Nias, and possibly the Mentawai Islands ). The type locality given is "Sumatra."
According to Gumprecht et al. (2004), the records regarding its occurrence in the Mentawai Islands are probably based on T. hageni.
It is nocturnal, climbing onto low branches to hunt its prey.
Because it is a large snake with large fangs, Trimeresurus sumatranus can inject large quantities of venom. Fatalities from its bite have been reported, and it should be considered extremely dangerous.
