There are more than 3000 species of snakes in the world. For the purpose of clinical
practice, snakes are classifi ed into poisonous (venomous) and non-poisonous (non
venomous) snakes. Poisonous snakes are classifi ed into three families and they are
• Cobra group [Elapidae]
• Viper group [Viperidae]
• Sea snake group [Hydrophidae]
For many decades, the concept of the “Big 4” snakes of medical importance has
refl ected the view that 4 species and responsible for Indian snakebite mortality. They are
– the Indian cobra (Naja naja), the Common Krait (Bungarus caeruleus), the Russell’s
viper (Daboia russelii) and the Saw scaled viper (Echis carinatus). However, recently
another species, the Hump-nosed pit viper (Hypnale hypnale), has been found to be
capable of causing lethal envenomation, and that this problem had been concealed
by systematic misidentifi cation of this species as the saw-scaled viper. The concept
of the “Big 4” snakes has failed to include all currently known snakes of medical
signifi cance in India. This has a negative effects on clinical management of snakebite
and the development of effective snake anti venoms
In 1981, the W.H.O. developed the following defi nition of snakes of medical
importance (Table No.2). This model is more accurate and useful than defi nitions such
as the ‘Big 4’ that are inaccurate and misleading to doctors and more importantly to
ASV manufacturers.
Table No. 2: Categorisation of snakes (W.H.O. 1981)
Class Details Name of the snakes
| I Commonly cause death or serious disability | Russells viper / Cobra / Saw scaled viper |
| II Uncommonly cause bites but are recorded to cause serious effects (death or local necrosis) | Krait / Hump-nosed pit viper /
King cobra / Mountain pitviper |
| III Commonly cause bites but serious effects are very uncommon. | Water snakes, Green snake |
Snakes of Medical Importance in Tamil Nadu – Distinguishing
features
A great deal is written concerning the problem of how to identify medically
signifi cant species from non signifi cant ones. A large amount of space is devoted, in
both medical and toxicology textbooks, to the problem of how to identify venomous
snakes. The problem with this information is that it is complex (involves counting
of scales) and not defi nitive (the identifi cation of pre or post maxillary teeth) and of
no use to a doctor in a medical situation. On the question of description, it is worth
remembering that the least reliable means of identifying a particular species of snake
is to use colour. Virtually every species of venomous snake has a huge range of colour
manifestations and even the markings can be subjected to major variations. What is
important therefore is to focus on the key aspects of identifi cation that enable the
medical professional to rapidly identify whether they are dealing with a venomous
species, and what that species might be.
There are six medically important species in Tamil Nadu shown above. Readers are
informed to get familiarised with the pictures given at the end of Hand-book. Further
details of some of the poisonous snake are provided in the ensuing paragraphs.
Russell’s Viper (Daboia russelii)
The Russell’s Viper is a stout bodied snake, the largest of which grows to
approximately 1.8 meters in length. Like all the vipers it is a nocturnal snake, but
unfortunately for humans, during the daytime it rests up under bushes, at the base of
trees and in leaf litter. It is therefore frequently encountered by rural workers, as they
are carrying out general agricultural activities.
There are two key identifi cation features that are worth noting. The fi rst is a series
of chain-like or black edged almond shaped marks along the snakes back and fl anks.
The second distinguishing mark is a white triangular mark on the head with the apex
of the triangle pointing towards the nostrils.
Saw scaled Viper (Echis carinatus)
The southern Indian Saw Scaled Viper is a small snake, usually between 30 and 40
centimetres long. The northern Indian species (Echis sochureki) is much larger, with
an average size of 60 centimetres. It inhabits mainly dry arid climates but can also be
found in scrubland.
One of the key identifi cation features of this species is the posture it adopts when
it is agitated. It moves its body into a fi gure of eight like arrangement with its head
at the centre. It rapidly moves its coils against each other and produces a hissing like
sound which gives its name of ‘Saw Scaled’. In addition, there are often wavy hoop
like markings down both sides of the Saw Scales body. On the head, there is usually
a white or cream arrow shaped mark, pointing towards the front of the head, often
compared to the shape of a bird’s foot.
The Hump-nosed Pit viper (Hypnale hypnale)
The Hump-nosed pit viper is one of India’s tiniest venomous snakes, its total length
ranging from 28.5 to 55cm. Its distinctive features include the presence of fi ve large
symmetrical plate scales on the top of the head in addition to the smaller scales typical
of all vipers. There are heat sensitive pits between the nostril and the eye.
Spectacled Cobra (Naja naja)
The Spectacled Cobra, is probably India’s most well recognised snake. The hood
markings of the spectacle like mark, distinguishes this snake from other species, and
its habit of rearing up when alarmed makes it distinctive but not defi nitive as otherspecies do this, notably the Trinket Snake. The Cobras coloration may vary from pale
yellow to black.
Common Krait (Bungarus caeruleus)
The Common Krait is a nocturnal snake which usually grows to approximately
1.0 to 1.2 metres in length. Its primary diet is other snakes. It can be found all over
Peninsular India and often seeks habitation near human dwellings. During the day it
rests up in piles of bricks, rat burrows or other buildings. The Common Krait is the
most poisonous snake in India and its venom is pre-synaptic neurotoxic in nature.
There are a number of key identifi ers which are worth remembering. The Krait
is black, sometimes with a bluish tinge, with a white belly. Its markings consist of
paired white bands which may be less distinct anteriorly. These paired white bands
distinguish the snake from another black nocturnal snake, the Common Wolf Snake.
The Wolf Snake’s white bands usually are thicker and are singular bands equidistant
from each other. The second useful distinguishing feature is a series of hexagonal
scales along the top of the snakes back. This feature is really useful if the dead snake
has been brought to the hospital and examined.
King Cobra (Ophiophagus hannah)
The King Cobra is the least medically signifi cant of the venomous snakes in India
in terms of both bites and fatalities. Hence, descriptive features of this are not provided
here