Our post-release monitoring (PRM) team patrols the forest transects in search of orangutans, but they always keep their eyes open for other potential encounters. Sometimes they meet exciting wild animals such as maroon langurs (Presbytis rubicunda) and Bornean gibbons (Hylobates muelleri). Recently, in the Kehje Sewen Forest, our PRM team stumbled across an animal that they recognised instantly from its iconic shape and colour. This animal can be found on tree branches and even on the ground. Yap! It is a sumatra pit viper (Trimeresurus sumatranus) from the Viperidae family.

The body of the sumatra pit viper is green-yellowish with black-cross in adults and green in juveniles. They also have a triangular head and gold-yellow irises. The striking dark green colour makes this snake difficult to see when it is in a tree.

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The sumatra pit viper has venom that is a hemotoxin, so it attacks the circulatory system. The effects can include tissue damage, swelling, widespread stiffness and pain, nausea, heart arrhythmia, and even death. Therefore, it is better not to disturb or approach carelessly when encountering this snake. 

The sumatra pit viper is a nocturnal animal that often looks for prey at night. During the day, it will sleep curled up on a tree branch. Even though it has a short tail, the Sumatra pit viper can still hold tree branches firmly. This snake generally eats birds, reptiles, amphibians, and small mammals.

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The sumatra pit viper is distributed across southernmost Thailand, Peninsular Malaysia, Borneo, sumatra, and several other smaller islands in Indonesia. In Borneo, this snake has been recorded inhabiting areas at an elevation of 1,178 m, which is the highest known record for this species. The habitat of the Sumatra pit viper is forests, especially tropical forest areas that contain bamboo thickets and low bushes along rivers.

Currently, the sumatra pit viper is categorized as a species of least concern by the International Union for Conservation of Nature and Natural Resources (IUCN). Our meeting with Sumatra pit viper was something unexpected and even though they can be dangerous, their conservation must still be protected. Left alone they function as an important part of their ecosystems and they are needed to maintain balance!

Text by: PRM Team at Camp Lesik, Kehje Sewen Forest, East Kalimantan