Trimeresurus nebularis, or the Cameron Highlands Pit Viper is a species under the family Viperidae, subfamily Crotalinae (pit vipers). It is also known as the Clouded Pit Viper (Baker, 2020; Uetz et al., 2020) and in vernacular, Ular Kapak Cameron Highland. The specific epithet is derived from the Latin, meaning ‘from the cloud’. This gives the impression that this species inhabits montane rainforests or cloud forests. The Cameron Highlands Pit Viper was first described in 2004 and is found in the mountain ranges south of Pahang, at elevation of around 1500 m. It is an important mesopredator of montane forest ecosystems. This species was subsequently discovered at Fraser’s Hill, 100 km away to the south of the Cameron Highlands. The southernmost encounter of this species was at Genting Highlands (an unreported bite incident). This montane pit viper has been found at elevation ranging from 1000 to 1500 m and is mainly distributed along the central part of the Titiwangsa mountain range, and has been more recently found in southern Thailand (Das, 2012).
Trimeresurus nebularis males can attain about 100 cm, while females reach at least 95 cm. It has a robust and cylindrical body, the head and the neck can easily be distinguished; it’s pupil is vertical within a yellowish green or green iris. The body dorsum is bright green, with a hint of blue. The upper labials scales are usually bluish-green, while the throat and chin are yellowish green. Ventrolateral stripe and postocular streak are typically absent. The tail is green laterally and its vertebral region rusty brown, with a sharp line in between (Sumontha et al., 2011). Trimeresurus nebularis can be distinguished from congeneric pit-vipers, such as Trimeresurus popeiorum (Pope’s Pit Viper) by the clear border between green and brown colours of tail. The iris of eye is red in adults or yellow in juvenile T. popeiorum. Generally, T. nebularis has a lower scale count of supraoculars, subcaudals and ventrals compared to congeners. Trimeresurus sabahi fucatus (the Thai Peninsular Pit Viper), which has a similar distribution in the Malay Peninsula, has a few common characteristics with T. nebularis that may result in the two being confused. However, adult T. sabahi fucatus is smaller in size, has yellowish iris and distinctive ventrolateral stripes (white or red) and higher counts of midbody and caudal scales (Ismail et al., 2022; Charlton, 2020). Birds and small mammals are likely to be part of its diet (Wong, 2018).
Trimeresurus nebularis is venomous and its bite can potentially cause coagulopathy (bleeding disorder) in humans. Based on the Remote Envenomation Consultancy Services (RECS) database in MyBIS Toxinology Module, plantation workers and those working in the agricultural industry in Cameron Highlands are most frequently bitten (Ismail, 2015). The Thai Green Pit Viper Antivenom (GPVAV) has been shown to cross-neutralise T. nebularis venom (Tan et al., 2019), and is used to treat envenoming syndrome from T. nebularis. The GPVAV has been adequately stocked for pit viper bite envenoming at Sultanah Hajah Kalsom Hospital, Tanah Rata, since 2014. Based on the RECS 2014-2022 database, there was no mortality resulting from envenoming of T. nebularis.
T. nebularis is listed as Vulnerable (VU) under the IUCN Red List of Threatened Species, due to its limited distribution, reaching a maximum of roughly 6,600 km² area in central highlands of Peninsular Malaysia (Grismer, 2012). Nonetheless, the number of mature snakes getting killed following human-animal conflict is increasing. This issue is made worse by unauthorized collection for the pet trade. If this species continues to be hunted, it may progress to higher threat category in the near future.
