Species in Focus: Sunda Island Pit Viper

Species in Focus is a series of short posts about interesting species I’ve seen with tips on identification and where you can also see them.

Identification: The Sunda Island Pit Viper (Trimeresurus insularis) looks a lot like many of the other green pit vipers that are found across Asia and shares its range with the very closely related White Lipped Pit Viper (Trimeresurus albolabris). This makes identification very difficult as both species are green, have keeled scales and have 21 longitudinal scales rows on mid body (scale counts are often used for tricky snake identifications).

So why are they considered different species if they look the same? It all comes down to genetic differences and they form what is known in biological terms as a species complex – a group of closely related species that are very similar in appearance to the point that the boundaries between them are not clear. I appreciate that this doesn’t help you to identify one in the field though. Generally speaking if you are somewhere west of Central Java then it will be the white lipped pit viper and if you are somewhere east of Central Java then it will be the Sunda island pit viper. If you’re in Central Java where they both occur then your guess is as good as mine!

It is a small species of snake (around 40-80cm) with females being much larger and heavy bodied than the males.

Male Sunda island pit viper (Trimeresurus insularis) in Bali, IndonesiaMale Sunda Island Pit Viper (Trimeresurus insularis), Bali.

Behaviour: A nocturnal snake that primarily lives in trees and shrubs, using its prehensile tail to grip branches. Whilst in Bali I encountered them in bushes at waist height but also in tall trees. They feed on birds, small mammals, frogs and lizards which they quickly subdue with a powerful venom. The venom is dangerous to humans and can be potentially life threatening. Symptoms include severe pain, swelling, blistering and internal bleeding due to the venom affecting the blood’s ability to clot properly. Having said that, this snake is not aggressive but will defend itself if threatened or accidentally walked into, grabbed or trodden on. If you are lucky enough to see one just keep a respectful distance.

Sunda island pit viper (Trimeresurus insularis) flicking its tongue, Bali Male Sunda Island Pit Viper (Trimeresurus insularis, Bali

Where to see: Found in Indonesia and Timor Leste it is a common species throughout its range. Head out after dark and search trees and bushes by eye. You can often see them in the foliage that borders rural roads.

Did you know? On the island of Komodo the Sunda Island Pit Viper is a beautiful blue colour and on the island of Wetar it is bright yellow!

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