Organic irritants are poisons that have a plant or animal origin. Poisoning from plants is common as they are easily available almost everywhere in the vicinity of human beings. But the poisoning through animal bites is not frequent, especially from wild animals.

However, pet animals like cats and dogs do bite human beings frequently, but poisoning caused by them is less common. The most poisonous animals include poisonous snake, which causes lethal poisoning in human beings.

Snakes are cylindrical, long, limbless, cold-blooded reptiles. There are a varied number of snake species present on earth but not all of them are poisonous in nature. Only a few species of snakes are poisonous, due to the presence of a zootoxin called ‘venom‘ produced by the salivary gland.

There are about 3500 species of snakes known amongst which about 350 species are venomous. In India, about 216 species are found and among them, about 52 are poisonous.

What is Venom?

Venom is the toxic saliva secreted by the salivary glands in snakes, as a part of their defense as well as an attacking mechanism.

The salivary glands that are situated at the back of the head of the snake, secret this zootoxin and injected it into the prey’s body through hollow fangs (that act like hypodermic needles).

When the snakes bite their prey, the fangs present in the mouth press the muscles of the salivary glands which squeeze out the venom into the fangs, transferring it into the body of the prey.

The venom contains a lot of toxic principles which include- Toxalbumins, cholinesterase, fibrinolyses, neurotoxins, mycotoxins, cardiotoxins, agglutinins, proteolysis, thromboplastin, hemolysins, and many other derogatory enzymes.

The venom secreted by snakes usually produces three types of toxic effects:

  • Neurotoxic Effects– Venom causes paralysis and convulsions.
  • Vasculotoxic Effects– Venom causes the destruction of blood vessels as well as blood cells that may cause hemorrhages in the brain.
  • Myotoxic Effects– Venom causes deleterious effects on muscles leading to muscular pains and respiratory failures too.

Morphology of Snakes

  • The body of the snake is divided into the Head, trunk, and tail.
  • They do not have any limbs or external ears.
  • Their whole body is covered with dermal scales, which are shed off from time to time and regenerated, as a mechanism of growth and removal of harmful parasites.
  • All the snakes belong to the Serpentes suborder of class Reptilia.

Difference Between Poisonous & Non-Poisonous Snakes

As discussed above, not all snakes are poisonous, a large species of snakes are non-poisonous. This classification of snakes is based on medicolegal purposes and they can be differentiated by their morphological characteristics easily. Some of the basic differentiation features of poisonous and non-poisonous snakes are discussed as follows:

Difference between Poisonous and non-poisonous snakes
Difference between Poisonous and non-poisonous snakes

1. Head Scales

In poisonous snakes, the scales are usually small but some species contain large head scales with special features like- a pit between eyes and nostrils (pit viper), a third supralabial touching the eye and nasal shield (cobra), a fourth infralabial shield (kraits), etc.

Non-poisonous scales contain only large scales without any special features.

2. Belly Scales

In poisonous snakes large belly, scales are present that covers the entire breadth of the belly, whereas non-poisonous snakes contain small or moderately large scale that never covers the belly.

3. Fangs

The poisonous snakes have large teeth modified into fangs that inject venom into the prey. On the other hand, non-poisonous snakes have small teeth and fangs are absent.

4. Tail

The tail of poisonous snakes is compressed while that of non-poisonous snakes is rounded.

Common Poisonous Snakes in India

1. Cobras: Common cobra, King cobra.

2. Kraits: Common krait, banded krait.

3. Vipers: Russell’s viper, Saw-scaled viper.

4. Sea Snakes: Banded sea snakes, and amphibian sea snakes.

Common Non-Poisonous Snakes in India

1. Rat snake (Dhaman)

2. Vine snake

3. Bronze back tree snake

4. Banded kukri

5. Sand boa

Non-poisonous snakes, at times, may resemble poisonous snakes and create confusion.

Poisonous Snakes

Poisonous snakes are further categorized into five families based on the difference in their morphological characteristics, dentition, osteology, types of venom, etc.

  1. Colubridae: It is the most widespread family of snakes, that is distinguished by the absence or significant reduction of the left lung, the lack of teeth on the premaxilla, and typically possess a loose facial structure, few head scales, and ventral scales that are as wide as the body. The venom produced by these snakes is not lethal but may cause some local effects. Example: African boomslang snake, twig snakes.
  2. Alractaspididae: They have small heads, smooth scales without apical pits, small to tiny eyes with circular pupils, and no loreal scale is all characteristics of these snakes. Burrowing asps (Atractaspis), one species, have unusually upright front teeth. The venom secreted by these snakes produces some potent smooth muscle contractions. Example: mole vipers or adders.
  3. Elapidae: This is a family of venomous snakes characterized by hollow, permanently erect, relatively short fangs in the front of the mouth that channel venom into the prey. The venom produced by these snakes is neurotoxic in nature. Example: cobra, krait, coral snake.
  4. Viperidae: All viperids have two moderately lengthy solenoglyphous (hollow) fangs that are used to inject venom from glands that are situated just behind the eyes near the back of the upper jaws. The two fangs are located on a short, movable maxillary bone at the front of the mouth. The fangs are covered in a membrane sheath and fold back against the roof of the mouth when not in use. Their venom is vasculogenic in nature. Example: Russell’s viper, saw-scaled viper.
  5. Hydrophidae: This family consists the aquatic snakes, especially sea snakes, and was formerly considered to constitute a subfamily of the family Colubridae. They produce myotoxic venom. Example: Sea snakes.

Some of the Poisonous Snakes in India are:

a) Indian Cobra

  • Scientific name: Naja naja
  • Common name: Common cobra, nag
  • Geographical Area: India, China, Philippines, Africa, Tasmania, Australia, New Guinea, and Egypt.
  • Length: 1.5-2 meters
  • Common cobras are usually brown or black in color
  • The head is covered with shields. The third supra-labial shield touches the eye and nose. A small wedge-shaped scale called cuneate is present between the 4th and 5th infra-labials. Round pupils are present.
  • A hood is present, where monoacetate (monocle) or binocellate (spectacle) mark on the dorsal side two dark spots on the ventral side are present.
  • Venom– Neurotoxic
Naja naja
Naja naja

b) Green Pit Viper

  • Scientific name: Trimeresurus albolabris
  • Common name: Green pit viper, Bamboo snake, Hara phisi
  • Geographical Area: Southeast Asia
  • Length: 30-100 cm
  • This snake is usually vivid green in color and rarely yellow or brown. The head is triangular and wider than the neck. covered with small scales called shields. The third supra-labial shield touches the eye and nose. A small wedge-shaped scale called cuneate is present between the 4th and 5th infra-labials. Vertical pupils are present.
  • Well-marked large, canalized and movable fangs are present.
  • Venom– Vasculotoxic.
Trimeresurus albolabris
Trimeresurus albolabris

c) Banded Krait

  • Scientific name: Bungarus fasciatus
  • Common name: Banded krait
  • Geographical Area: India and China
  • Length– 2 meters
  • The back of the body shows a pattern of alternate yellow and black bands. The head is big and not distinguished from the neck. The mouth has four infralabials, with the fourth one being the largest. The back of the body has a central row of hexagonal scales. Eyes have round pupils.
  • Small and erect fangs are present.
  • Venom– Neurotoxic
Bungarus fasciatus
Bungarus fasciatus


Snakes are the most common examples of animals causing poisoning to human beings. The zootoxin present in them, called venom causes toxicity in human beings. Venom is an organic compound that contains toxalbumins and other harmful substances.

There are three major harmful effects caused by zootoxin- neurotoxic, vasculotoxic, and myotoxic, which also form the basis for the division of snakes into various categories.

Snakebite cases are usually encountered in accidental poisoning but are also encountered in homicidal poisoning.

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Frequently Asked Questions

1. Which is The No. 1 Poisonous Snake in India?

Saw-scaled viper is considered as the deadliest snake in India in terms of kills. This snake has caused more fatalities in India than many other snakes combined.

2. Which is The Biggest Snake in India?

Indian-Rock Python is considered one of the biggest snakes in India that can be as heavy as 90 kilograms and 15-20 feet in length. It is one of the three species of pythons found in India.

3. How Toxic Are Sea Snakes?

Yes, Sea snakes are poisonous. Their bite may be painless but their venom is poisonous and may show symptoms in a few minutes to a few hours. The Dubois sea snake is the most dangerous of all.

4. Which Animal Has no Anti-Venom?

Blue Coral Snakes are pretty thin and a couple of death have been reported due to these snake poisons. They grow up to 6 feet and may kill horribly. Their anti-venom has not been developed yet.

Categories: Toxicology


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