Snakes

Legless reptiles, and how they manage without limbs.

Snakes are legless reptiles with elongated bodies, no eyelids and no external ears. There are around 4,000 species; a minority are venomous, and a smaller minority are dangerous to people.

Movement without legs

• Lateral undulation — S-shaped waves pushing against surface irregularities. The default.
• Rectilinear — belly scales gripping and pulling in a straight line. Used by heavy-bodied species.
• Concertina — anchoring one part while extending another. For climbing and tight spaces.
• Sidewinding — throwing loops sideways with minimal contact. For loose sand.

Feeding

Snakes swallow prey whole. The lower jaw halves are joined by an elastic ligament rather than fused, and the skull bones are loosely connected, so the mouth can open far wider than the head. Backward-pointing teeth walk the prey inward. Digestion is slow and metabolically expensive, which is why large meals are infrequent.

Senses

The forked tongue collects scent particles and delivers them to the Jacobson's organ; the fork gives a directional reading, which is why the tongue flicks so constantly. Pit vipers, pythons and boas also have heat-sensing pits that detect infrared, letting them strike warm prey in complete darkness.

Identification, carefully

Popular rules — head shape, pupil shape, rhyme schemes about colour bands — are regionally unreliable and have all produced bites. The safe rule is simple and does not require identification: do not handle a snake you cannot identify with certainty, and learn the specific dangerous species of your own region from a local authority.