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Meet the new species of venomous pit viper described from India

Newly described Arunachal pit viper has a pointed snout. Image by Rohan Pandit.

  • Wildlife researcher Rohan Pandit and his teammate Wangchu Phiang first stumbled upon the new-to-science pit viper species in May 2016 while surveying biodiversity in the state of Arunachal Pradesh in India.
  • In a new paper, researchers have described this species and named it Trimeresurus arunachalensis, or Arunachal pit viper.
  • While the researchers have described the Arunachal pit viper based on a single specimen, they say the species’ unique features distinguish it from all the other known species of pit vipers.

When Rohan Pandit and Wangchu Phiang accidentally stumbled upon a brown snake on a steep slope of a forest in the northeastern state of Arunachal Pradesh in India, little did they know that the reptile had never been formally described before. Now, in a new paper, researchers have described this snake as a new-to-science species of pit viper named Trimeresurus arunachalensis, or Arunachal pit viper.

Both Pandit, an Indian wildlife researcher and a co-author of the paper, and Phiang, a member of the indigenous Bugun tribe, were part of a biodiversity survey project at the time. They had been walking through a forest near the village of Ramda in West Kameng district when Phiang spotted the snake amid the leaf litter.

He pointed it out to Pandit, and the latter was quick to note that the snake was a species of viper, a group of venomous snakes with folding fangs, but unlike any other viper he’d encountered in India before. “At that time we really had other priorities. We had to reach another place, so we just bagged the snake,” Pandit said. “Later on when we returned to the camp we checked it properly. It was pretty apparent then that it was something I had never seen before in any snake book.”

What caught Pandit’s attention was the snake’s “peculiar” pointed snout that resembled that of the hump-nosed viper (Hypnale hypnale). The hump-nosed viper, however, is found farther away in peninsular India and the Western Ghats. “At first, I was surprised that maybe hump-nosed vipers are also found in northeast India,” Pandit said. “There are also similar looking snakes in Borneo and southeast Asia … so initially we thought this snake might be a range extension of those species.”

The Arunachal pit viper was found in the state of Arunachal Pradesh in northeast India. Image by Rohan Pandit.

To get a clearer picture, a team of researchers, including Pandit, went on to study the specimen in detail. They took measurements of the animal, noted its number and pattern of scales, and analyzed its anatomy, comparing them to those of all other known species of vipers found in Asia. They also extracted DNA from it and analyzed it in a lab at the Indian Institute of Science (IISc) in Bengaluru (formerly Bangalore), said Deepak Veerappan, currently a herpetologist at the Natural History Museum, London, who was a postdoctoral student at IISc at the time of the analysis.

The researchers found that the Arunachal pit viper had a very different scale count compared to all known mainland pit vipers of northeast India and nearby China. Results from genetic analysis added further evidence that the species Pandit had encountered was indeed a new one, closely related to the Tibetan pit viper (Trimeresurus tibetanus), a snake known only from Tibet. But physically and anatomically, the two species are quite distinct, the researchers say.

The Arunachal pit viper’s hemipenis (the snake’s paired reproductive organ), for example, is especially strikingly different from that of the Tibetan pit viper, Veerappan said. “I have been studying hemipenial morphology of snakes and lizards for a while now. The first time I saw the hemipenis of the snake [I realized] it is unique compared to its congeners,” he said.

The snake’s coloration is also striking. “If you look at it from the top, it appears drab and camouflages well against leaf litter,” Pandit said. “But on the sides and the belly they have a bright orangish color.”

The Arunachal pit viper camouflages well in leaf litter. Image by Rohan Pandit.

The researchers have described the Arunachal pit viper based on a single specimen. But Veerappan said the species has many “unique features compared to all the known species in the genus,” and their analysis of the snake’s molecular, external and internal anatomy confirmed that it is a new species. “Therefore, I do not think this is a limitation,” he said.

Pandit, who is also confident of the snake’s standing as a new species, said describing it as such based on a single specimen meant several things still remained unknown. “There are [a] lot of things that we don’t know,” he said. “For example, for snakes, their scale count is always given as a range after studying a lot of specimens. In this case, we have only one.”

Similarly, although the Arunachal pit viper was seen on the ground during the day, Pandit said they’re unsure whether the snake is completely terrestrial.

As for its habitat, Pandit and Phiang found the only known specimen, now deposited at the State Forest Research Institute in Itanagar, Arunachal, in an unclassified forest that adjoins Pakke Tiger Reserve. The closest village to the forest is Ramda, Pandit said, and while the villagers venture there sometimes to collect things like cane, the forest is only mildly disturbed and occurs on very steep terrain.

Future surveys of the forest may yield more individuals, which can fill in the information gaps. For now, though, the discovery of a new-to-science species has been very exciting, Pandit said. “It just confirms our previous thought process that there would be lots of undescribed species in these forests,” he said.

Banner image of Arunachal pit viper by Rohan Pandit.


Captain, A., Deepak, V., Pandit, R., Bhatt, B., & Athreya, R. (2019). A New Species of Pitviper (Serpentes: Viperidae: Trimeresurus Lacepède, 1804) from West Kameng District, Arunachal Pradesh, India. Russian Journal of Herpetology26(2), 111-122.

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