Arunachal pit viper: How researchers chanced upon a snake species that hadn’t been described before

The new-to-science Arunachal pit viper was perfectly camouflaged among dry leaf litter when Rohan Pandit and Wangchu Phiang accidentally stumbled upon it when out on a march through a forest in Arunachal Pradesh.

At first sight, Pandit, a wildlife researcher, and Phiang, a member of the indigenous Bugun tribe, did not realise they had stumbled upon something that had never been formally described before.

They were walking through a forest near the village of Ramda in West Kameng district as part of a biodiversity survey project 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.”

Now, a new paper has described this snake as a species of pit viper named Trimeresurus arunachalensis, or Arunachal pit viper.

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 North East 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.”

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 analysed its anatomy, comparing them to those of all other known species of vipers found in Asia.

They also extracted DNA from it and analysed it in a lab at the Indian Institute of Science in Bengaluru, said Deepak Veerappan, currently a herpetologist at the Natural History Museum, London, who was a postdoctoral student at the IISc at the time of the analysis.

Different scale count

The researchers found that the Arunachal pit viper had a very different scale count compared to all known mainland pit vipers of North East 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,” he said. “The first time I saw the hemipenis of the snake [I realised] it is unique compared to its congeners.”

The snake’s colouration 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 colour.”

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.

This article first appeared on Mongabay.