Snake

Surviving without legs

Snakes evolved from lizard-like ancestors that lost their legs approximately 100-150 million years ago. The transition to leglessness came with several adaptations:

• Elongated body — extra ribs, more vertebrae (often 200+).
• Forked tongue — collects scent particles, flicks them onto a vomeronasal organ.
• Heat-sensing pits (in some families) — detect warm prey in darkness.
• Sophisticated jaw mechanics — hinged at multiple points for swallowing large prey.

Some lizard families (like glass lizards) have independently evolved leglessness, but snakes are by far the most diverse and successful legless squamates.

Jaw mechanics

A snake doesn’t actually “unhinge its jaw” — popular myth. The reality is more interesting:

• The lower jaw is in two halves connected by elastic ligaments.
• Each half can move independently.
• The upper jaw articulates with a separate pterygoid bone.
• Multiple flexible joints allow the entire skull to expand around prey.

The result is a swallowing system that can engulf prey far wider than the snake’s head. Pythons can swallow deer; eagles have been documented being swallowed by some species.

Venom systems

Of 3,800+ snake species, about 600 are venomous to humans. Venom delivery varies:

• Front-fanged (vipers, cobras) — hollow fangs at front of mouth, fast injection.
• Rear-fanged (some colubrids) — small fangs at back; less efficient delivery.
• Spitting cobras — modified fangs that aim venom at predator eyes.

Snake venoms are often complex chemical cocktails:

• Neurotoxins — affect nervous system (cobras, mambas).
• Hemotoxins — affect blood and tissues (vipers, rattlesnakes).
• Cytotoxins — destroy cell membranes (some cobras).

Most snakebites globally are by vipers (saw-scaled vipers in Asia/Africa) — they’re the most-encountered medically dangerous snakes worldwide.

Snake-free Ireland

Ireland famously has no native snakes — a result of the last ice age. As Europe warmed and snakes spread northward from refugia, Ireland was already isolated by sea, and the cold British/Irish climate slowed colonization. By the time snakes reached Britain, sea levels had risen, cutting Ireland off.

The folk story credits St. Patrick with driving the snakes out — but there were never any to drive. The same applies to Antarctica, Iceland, Greenland, and New Zealand.