Family : VIPERIDAE
Species :  Trimeresurus fucatus
Maximum Size : 86 cm

The 'Siamese Peninsula Pit Viper' Trimeresurus fucatus was first described as a separate species in 2004, prior to which it was considered a variant of Pope's Pit Viper. 

There is significant local variation in patterning. A dual stripe (white over red) generally extends along each flank (i.e. a dorsolateral stripe), though in some specimens the red stripe may be absent and in others both stripes may be absent.

Red-over-white postorbital stripes (i.e. those immediately behind the eye) occur in many specimens, but in others this feature too may be entirely absent. (In some populations this  feature may occur exclusively in males, though this is not certain). Regular, dark banding may occur over the back, but this is generally very faint. The skin between the scales (interstitial skin) can have a bluish tinge. The belly is pale green. Iris colour may vary from orange-red to yellow to green.

The upperside of the tail is reddish brown, and the underside of the tail is pale: demarcation between these two colours is typically indistinct (and often has a saw-tooth pattern). This is in contrast to the Cameron Highlands Pit Viper Trimeresurus nebularis where the demarcation between the upperside of the tail and underside is sharp.

The scales of Trimeresurus fucatus are typically matte - note the lack of reflected light under flash photography in the images shown here.

Grismer et al (2006) graphically illustrated the variation in patterning of this species on Pulau Langkawi, Peninsular Malaysia.

This stunning pit viper occurs in southern Thailand and Peninsular Malaysia, with an apparent stronghold on Pulau Langkawi.
 

Fig 1 : Example from Fraser's Hill, Peninsular Malaysia which had recently consumed a small squirrel: note the marked bulge in its middle of its body.

Figs 2 and 3 : Adult specimen found resting on a sapling in lowland forest at Datai Bay, Pulau Langkawi, northern Peninsular Malaysia. Note the well-developed red and white stripes behind the eye and along the flanks, and faint brown banding across the body.

Fig 4 : Specimen from Fraser's Hill, Peninsular Malaysia at 1000 metres elevation, with lateral red and white stripes but no facial markings.

Fig 5 : Adult specimen from Gunung Tiong, Endau-Rompin, southern Peninsular Malaysia at an elevation of around 600-700 metres. Note the absence of any form of stripe or banding, except possibly for a faint pale dorsolateral stripe.  Photo thanks to Goh Si Guim.

Fig 6 : Specimen from Gunung Belumut, Johor, southern Peninsular Malaysia (elevation unknown). This snake (which appears to be digesting a meal) has a white ventrolateral stripe and a reddish-brown, banded tail.  Note the saw-tooth pattern on the tail. This may represent the southernmost record of the species to date. Photo thanks to Joseph Lim.


References :

Grismer, L., Youmans, T., Wood, P., Ponce, A., Wright, S., Jones, B., Johnson, R., Sanders, K., Gower, D., Yaakob, N., Lim, K. P. 2006. Checklist of the herpetofauna of Pulau Langkawi, Malaysia with comments on taxonomy. Hamadryad Vol 30. Nos. 1 & 2, pp. 61-74.