Snakes-their classification and Distribution in India

Snakes-their classification and Distribution in India

E.Kunhikrishnan

Sr.Lecturer, Department of zoology

H.H.Maharaja University College

Thiruvananthapuram

INTRODUCTION

There are about 2920 species of snakes belonging to 445 genera in the world; under 18 families

About 200 species are found in India.The maximum diversity of snakes in India is in the Western Ghatsand in the  North east. 

The snakes are commonly divided in to two infraorders , Alethinophidia with  15 families and  Infraorder Scolecophidia with 3 families 

The pattern of scale arrangement and the configuration of scales provide the most useful basis for identification. The  first step in learning to use dichotomous keys for snake identification is to become acquainted with the typical "scalation".

The scales on a snake's body are either "smooth" or "keeled". A keeled scale has a ridge down the middle of the scale. A smooth scale has no ridge. 

The cloacal opening is covered with a scale, the anal, which may be single or divided into 2 parts. 

Anatomical features of the skull is important. The change in size and position of the quadrate, the vestiges of the pelvis, the structure and the position of fangs etc also differ from group to group. The arrangement of the scales on the head, viz.  nasal, internasal, prefrontal, frontal, supraoccular, parietal,rostrla, loreal, upperlabials, lowerlabials, post ocular and temporal help in distinguishing family, genera and species. The number of scales in the dorsal row is also taken in to consideration.

NONPOISONOUS SNAKES

Family  Typhlopidae. Scales uniform.  Typhlops consists of two Genera and 21 species (Indian sub-continent). They are tiny worm-like burrowing snakes which are non-poisonous. There are at least 14 species in India , five occurring in Kerala.

Family  Uropeltidae   consist of burrowing snakes seen only in  peninsular India and Sri Lanka. Total  47 species in the world  of which 33 endemic to the Peninsular India. A group of great interest. 

Family Boidae   Include the biggest snakes in the world-boas and pythons  

There are two species of pythons in India, Python molurus - Indian Rock python and P. reticulatus-Nicobar Islands 

Genus Eryx consists of three species in India E.conicus, E.johnii and E. whitekeri 

Family Dipsadidae  Contain  some common snakes Genus like Lycodon.( Wolf snakes ). Misidentification of these harmless snakes creates problems because of their superficial resemblance to the deadly Kraits.

Eight species in India. Three in south India, Lycodon travancoricus (Travancore wolf snake), L. striatus  (barred wolf snake )and L. aulicus  (Common wolf snake )

Genus  Oligodon (Kukri Snakes) can be distinguished by peculiarand  prominat markings and pattern  on the head. 18 species in the Indian region; seven species present in south India, others in North east and in eastern Himalayas 

Genus  Amphiesma .Eight species. Three in Western ghats and south India, A. stolata (stripped keel back), A. beddome (Beddome's keelback) and A. monticola (green western keelback).

Genus Dendrelaphis -(Tree snakes) seven species in India. Five in south India, D. pictus (painted bronze back tree snake) D. grandoculis (large eyed brown tree snake)  D. bifrenalis( Boulenger's bronzeback treesnake ) D caudolineata (Stripetailed bronzeback tree snake )and  D. tristis (common bronzeback treesnake )

Family Colubridae includes well over half of all snake species on earth. Colubrid species are found on every continent, except Antarctica. There are 1938 species under 304 genera the world over. (All other snake species put together is about 980). While most colubrids are non-venomous (or have venom that isn't known to be harmful to humans) and are normally harmless, a few groups, such as genus Boiga, can produce medically significant bites, while the boomslang and the twig snakes have caused human fatalities. The venom is a modified form of saliva, secreted by glands in the upper jaw. The venom-injecting fangs of colubrids are termed opisthoglyphous, meaning that the small, grooved fangs are located in the back of the upper jaw, unlike those of vipers and elapids, which are located in the front. Even non-venomous colubrids often have fangs in this position, and use them to puncture egg-shells or similar food. Classification of Colubridae based mainly on dentition and other features. There are 3 sections. They are 1 Aglypha with solid ungrooved teeth, 2 Opisthoglypha with teeth are grooved and connected to poison-glands, 3 Proteroglypha with canaliculated anterior maxillary teeth (front-teethed) they are very poisonous. 

Aglyphous ("lacking grooves") snakes have no specialized teeth - each tooth is more or less the same in shape and often in size. When some teeth are larger than others, as is sometimes the case in bird eaters such as Corralus, the enlarged teeth are merely "scaled up", and are otherwise identical. Aglyphous snakes are non-venomous, and can be found in numerous families. Opisthoglyphous ("rearward grooves") snakes are similar to aglyphous snakes, but possess weak venom, which is injected by means of a pair of enlarged teeth at the back of the maxillae. These "fangs" typically point backwards rather than straight down, possess a groove which channels venom into the prey, and are located roughly halfway back in the mouth, which has led to the vernacular name of "rear-fanged snakes". This combination of features means that, in order to envenomate prey, the snake must bite it, move the prey into the back of the mouth, then penetrate it with the grooved fangs, which allow venom secreted into the mouth to seep into the prey. This presents difficulties with large prey items, though they can quickly move smaller prey (or a human handler's finger) into position. While the venom of most opisthoglyphous snakes is so weak that it does not affect humans, a few are capable of delivering harmful or even fatal bites. Notably, herpetologists Karl Schmidtt and Mertens were killed by aboomslang and theletornis, respectively, after each underestimated the effects of the bite and failed to seek medical help 

Proteroglyphous ("forward grooved") snakes have a much more sophisticated venom delivery method. These snakes have shortened their maxillae, which bears few teeth except for a substantially enlarged "fang" located at the front of the mouth. Unlike the opisthoglyphous snakes, the fangs of proteroglyphs point downwards and completely fold around the venom channel, forming a hollow needle with which to inject their venom more effectively. However, because the fangs are only a fraction of an inch long in even the largest species (and often much shorter) these snakes must still hang on, at least momentarily, as they inject the venom. The venom of proteroglyphs is the most toxic of all snakes, and among the most toxic natural substances in the world. This form of dentition is unique to elapids.

A few species of spitting cobras have modified opening at the tip of the fang which allows them to spray venom at an attacker's eyes. 

Subfamily  Colubrinae, is with over 100 genera and roughly 650 species in the world 

Genus  Elaphe -Nine species in Indian region but only one(Elaphe helena)--trinket snake) present in south India others are  in north east. 

Genus Chrysopelea -flying snakes- only two species, Chrysopelea ornata in the Western Ghats , Orissa, Bengal and the other species in Narcondam, Andaman islands. 

Genus Ahaetulla -vine snakes-6 species 4present in south India . A. nasutus is the  common vine snake. 

Family Homalapsidae 

Subfamily Boiginae –

Genus Boiga- Cat snakes ; 11 species  4 in south India; others in Assam and in northeast 

Genus Enhydris    include the Water snakes Three species, only two in south india.

POISONOUS SNAKES

Family Elaphidae: cobras; kraits; mambas; coral snakes; Australian taipan and tiger snakes 

Genus Bungarus (Kraits ) Sevenspecies  in Indian subcontinent. Only one in south India -B. caeruleus(Common krait). One of the most deadliest snake and is one of the "big four" snakes in India. Neurotoxicand quickly induces muscle paralysis. Clinically, their venom contains pre-synaptic neurotoxins. 

Genus Callophis (Coral snakes ) As the name indicates, beautifully coloured snakes. Five species in south Indian forests.  Venom: Uncertain possibly could have an adverse effect on human beings. However due to the paucity of venom found within this snake little scientific study has been conducted. However since it belongs to the family Elaphidae and nearly all Elaphids are venomous immediate medical assistance should be sought if a bitten by this snake. 

Genus Naja -Only one species but three sub species. Naja naja naja- Binocellate or spectacled cobra (common cobra) present throughout India.  Naja naja kaouthia --Monocellate /Monocled or Bengal cobra—Bengal, Assam and in Andaman. Naja naja oxiana  - black cobra -North  west region.

Genus Ophiophagus . Only one species in Asia - Ophiophagus hannah,  the king cobra. The largest poisonous snake.

Subfamily Hydrophinae Sea snakes  - 20 species -13 present in the west coast

Family Viperidae. Vipers (Latin vivus = alive + parere = bring forth meaning viviparous nature) consists of two Sub-families (Viperinae and Crotalinae)- In the family total there are 224 species in 32 genera distributed in Americas, Africa and Eurasia. Seven Genera and 31 species in the area comprising Indian sub-continent China and Malay Peninsula. They are one of the most widely distributed snakes in the world. 

Subfamily - Viperinae . 

Genus Vipera (Daboia) -two species  V. lebetina (Blunt nosed viper-laventine viper) Kashmir.  V. russeli -Russel’s viper – throughout India  including  High altitude like  Munnar.  A large triangular head help in identification. Its body is stout and cylindrical. Venom extremely lethal causes heavy internal haemorrhages. Death is caused by heavy blood loss due to internal bleeding.  

Echis carinatus  A small venomous snake of arid regions . Has a short snout and rounded cheeks. Often light brown in colour with a lateral row of dark brown outlined mottles. Lethally venomous. Its venom destroys red blood cells, the walls of arteries and reduces blood pressure

Subfamily Crotalinae - Pit Vipers 

Genus Agkistrodon (Hypnale)- 2 species one in Himalayas other in south  (Hypnale hypnale) 

Genus Trimeresurus - 14 species - 4 in south Indian  forests  -T macrolepis( large scaled pit viper) 

T malabaricus (Malabar pit viper ), T strigatus (Horse shoe pit viper) , T. gramineus (bamboo pit viper )

Of the roughly 725 species of venomous snakes worldwide, only 250 are able to kill a human with one bite. In south India cobra, viper, king cobra and krait only are coming in this category.

Photos by Dr.Pradeep Raj R.S.

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