Identification of Hypnale Zara (Hump-nosed Pit Viper) Using the Nuchal Colour Bands

Abstract

Hump-nosed pit vipers (HNV) of the genus Hypnale are medically important because they are the commonest cause of venomous snakebites in Sri Lanka. There are three species of HNV, namely H. hypnale, H. zara and H. nepa from which the latter two are endemic. The presence of ‘hump’ is the key identifying feature of HNV. All Hypnale species are lookalike to the naked eye. The objective of this study was to describe and differentiate the identification features of H. zara from the other two species. Specimens of HNV brought by snakebite patients to hospitals were collected from all over the country from February 2018 to January 2022. Their morphology, including gender, lengths, scale counts, and colour variations, were recorded. Killed specimens were preserved in 10% formalin, and live snakes were released to their natural habitat. Data analysis was done using SPSS version 21. Seventy-one specimens were studied, from which 45 were H. hypnale, 20 were H. zara and 6 were H. nepa. Out of H. zara, 13 (65%) were killed specimens, and 7 (35%) were live snakes. Twelve (60%) were males, and 8 (40%) were females. The lengths ranged as total length 229-425mm (mean 349, SD 63), snout to vent length 201-380mm (mean 300, SD 57), head length 14-30mm (mean 21, SD 4), and tail length 27-65mm (mean 49, SD 10). The number of scale counts were ventrals-148 (IQR 142-150), subcaudals-41 (IQR 37- 45), and mid-dorsal scales-17 (IQR 15-17). Characteristic colour bands were observed in all specimens of H. zara on either side of the neck compared to the other two species. These bands are thick and short, deep brownish in colour, three or more in number and the first is longer than the others. H. zara can be identified from the nuchal colour bands from the other two species of the genus. This is a characteristic feature of identifying H. zara.