Assam Keelback

Herpetoreas pealii, commonly known as Peal’s keelback or the Assam keelback, is a little-known natricine snake endemic to Northeast India. Once considered extremely rare, the species gained renewed scientific attention following its rediscovery in Arunachal Pradesh after a gap of 129 years. Historically placed under several genera, the snake has undergone multiple taxonomic revisions, reflecting changes in the understanding of natricine relationships in South and Southeast Asia.

Taxonomy and Nomenclature

The species has been assigned to various genera in historical literature, including Natrix, Paranatrix, Amphiesma, Hebius, and Herpetoreas. Its currently accepted placement is within Herpetoreas, a genus comprising Asian natricine snakes.
The specific epithet pealii commemorates Samuel E. Peal, an ethnographer and tea planter in nineteenth-century Assam. Peal collected the original specimens that enabled British zoologist William Lutley Sclater to describe the species as new to science. The naming follows the tradition of honouring contributors to natural history exploration in the Indian subcontinent.

Geographic Distribution and Habitat

Herpetoreas pealii is endemic to Northeast India, with confirmed records from the states of Assam and Arunachal Pradesh. These regions form part of the Eastern Himalayas biodiversity hotspot, characterised by evergreen forests, high rainfall and complex terrain.
The rediscovery of the species in Arunachal Pradesh underscored the ecological richness of the region and highlighted gaps in herpetological surveying. Although its precise habitat preferences are not comprehensively documented, available evidence suggests association with moist forested environments typical of natricine snakes.

Morphological Characteristics

This species is small and slender, attaining a maximum total length of roughly 50 cm, including a tail approximately 12.5 cm long. Its physical characteristics are distinctive, aiding in identification:

• Dorsal colouration: Dark brown with two pale lateral stripes on each side—an upper narrow stripe and a broader lower stripe two scales wide.
• Head patterning: The top of the head is uniformly dark brown. The rostral and labial scales are yellow, blotched and edged with brown.
• Ventral surface: Very dark brown ventrals laterally marked with pale yellow. A faint central yellow line becomes clearer towards the posterior.
• Dorsal scales: Strongly keeled, with reduced keeling in the outermost row; arranged in 19 rows at midbody.
• Ventrals and subcaudals: Ventrals number 142–144, the anal plate is entire, and the subcaudals range from 75–77, divided.

These traits were well documented in the nineteenth-century catalogue of the British Museum’s reptile collections, where the species was originally described under the name Tropidonotus pealii.

Reproductive Biology

Herpetoreas pealii is oviparous, consistent with reproductive patterns observed in many natricine snakes. Although detailed reproductive parameters—such as clutch size, breeding season and hatchling characteristics—remain unrecorded, the rediscovery of the species has renewed interest in gathering biological data through field studies.

Historical Context and Rediscovery

The species was first described in the late nineteenth century, after which it remained virtually absent from scientific observation. Its long period without confirmed sightings contributed to uncertainty regarding its conservation status and distribution. The rediscovery in Arunachal Pradesh has provided valuable new specimens for morphological and genetic assessment, prompting updated taxonomic work.
The historical misplacement of the species across several genera reflects the challenges faced by early herpetologists when relying largely on external morphology. Contemporary studies, integrating molecular data, have supported its current placement within Herpetoreas.

Significance in Regional Biodiversity

As a rare snake with a limited known distribution, Herpetoreas pealii contributes to the unique herpetofaunal diversity of Northeast India. Its rediscovery has highlighted the importance of systematic field surveys and habitat conservation in regions that remain underexplored. The species also serves as an example of how museum records and historical literature can guide modern biodiversity assessments.
Increasing forest fragmentation and environmental pressures in parts of Assam and Arunachal Pradesh may pose potential risks to populations of this little-known snake. Further ecological studies are needed to understand its population size, habitat needs and conservation priorities in a rapidly changing landscape.