Poisonous and Non-poisonous Snakes

Poisonous Snakes

  • Body colour generally bright.
  • Neck constricted.
  • Head long, triangular, and wide due to the presence of poison glands on two sides of the head.
  • In majority, a hood is present.
  • Tail abruptly tapering except in sea snakes.
  • Head shield very large.
  • The scales on the top of the head are small.
  • The scales on the dorsal surface of the trunk are smaller but spinal scales are large and hexagonal.
  • The ventral surface is covered with large transverse plates. No small scales are usually visible from below. All poisonous snakes must have broad plates on the belly but snakes having broad plates are not always poisonous.
  • Teeth are not uniform. The maxillary teeth are large and called ‘fangs.’ Fangs are grooved or with a canal.
  • Two poison glands are present.

Non-poisonous Snakes

  • Body colour not so bright.
  • Neck un-constricted.
  • Head usually narrow and elongated.
  • Hood usually absent.
  • Tail gradually tapering.
  • Head shield small.
  • The scales are large and usually nine in number.
  • The dorsal scales are large but spinals are smaller and not hexagonal.
  • Ventral surface is covered either with small scales or small scales are visible on both sides of the transverse plate below.
  • The teeth are uniform and solid  11. Poison glands absent.

Feacher of Non-Poisonous Snakes

  • Colour:  Usually not brightly coloured, but pythons, common sand boa, red sand boa, anaconda, wart snakes (Acrochordus granulatus), etc. are brightly coloured.
  • Shape of head: Head is usually narrow and elongated.
  • Neck: No constriction in the neck.
  • Hood: Hood absent.
  • Tail: Tail tapered and long except burrowing snakes. In Typhlopidae and Leptotyphlopidae the tail is short and stumpy. In Uropeltidae the tail is very short and rough. In sand boas also the tail is short and blunt.
  • Head scales: Scales on the top of the head are large but in sand boas(Eryx conicus) the head scales are small
  • Dorsal scales: Scales on the dorsal surface are longer but spinal (vertebral) scales are not longer and hexagonal.
  • Ventral scales: Ventral scales are either across the belly completely (e.g., Colubridae), or not completely across the belly (e.g., Boidae, Uropeltidae).
  • Loreal shield: Absent
  • Mental shield: Small
  • Caudal scales: Uniform and solid
  • Teeth: Uniform and solid
  • Poison gland: Absent
  • Muscular system: Well-developed strong muscular system.
  • Lungs: Both lungs are present.
  • Hypophysis: Hypophyses absent or present on the posterior dorsal vertebrae.
  • Streptostylism.
  • Less marked.

Example: Rat Snake (Ptyas mucosus), Indian Python (Python molurus), Sand Boa (Eryx conicus), Checkered keel back [Natrix (Xenocrophis) piscator], Wolf Snake (Lycodon aulicus), Striped Keel back (Amphiesma stolata).

Feacher of Poisonous Snakes

  • Colour: Generally brightly coloured
  • Shape of head: Head is long, triangular and posterior portion is wide.
  • Neck: Neck always constricted.
  • Hood: Present in majority cases; highly developed in Cobra group (Naja sp.); absent in Coral snakes, Krait, Russell’s viper, etc.
  • Tail: Tail is abruptly tapered, but in sea snakes (Hydrophidae) the tail is flat- tend to form an oar-shaped structure and in land snakes the tail is cylindrical.
  • Head scales: Scales on the top of the head are usually small.
  • Dorsal scales: Dorsal surface scales are smaller but the spinal (vertebral) scales are larger and hexagonal in kraits
  • Ventral scales: Ventral scales are usually completely across the belly but in sea snakes ventral scales are not completely across the body.
  • Loreal shield: Present, shapes may be variable.
  • Mental shield: Fourth one is large.
  • Caudal scales: Mostly undivided except coral and cobra snakes.
  • Teeth: Most of the teeth are solid and uniform except maxillary teeth which are large, and provided with groove or canal. These large teeth are called ‘Fangs’.
  • Poison gland: Present. Paired poison glands are on upper jaw.
  • Muscular system: Less-developed muscular system.
  • Lungs: One of the lungs has either been reduced or absent.
  • Hypophysis: Hypophysis developed throughout the vertebral column.
  • Streptostylism: Well-marked.

Examples: Saw Scaled Viper (Echis carinatus), Common Krait (Bungarus caeruleus), Banded Krait (B. faciatus), Russel’s Viper (Vipera russelli), King Cobra (Ophiopagus Hannah), Indian Monocled Cobra (Naja naja kaothia) etc.

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