Snake

Snakes are limbless reptiles with long, rope-like bodies covered in overlapping scales. They are ectothermic, which means their body temperature is largely set by their surroundings, and they breathe air.

Most snakes are fairly small, around 1 m (3.3 ft) long, though the group ranges from about 10.4 cm (4.1 in) to nearly 7 m (22.8 ft) for the biggest, the reticulated python. Snakeskin is smooth and dry, and the eyelids are clear, permanently closed scales called spectacles.

Snakes are carnivorous and swallow their prey whole. Most species are non-venomous. In captivity they are typically fed dead prey, because live rodents may fight back and injure them.

Snakes evolved from lizards, which genomic analysis, anatomy and fossils all support. They may have come from burrowing or aquatic lizards, and the earliest known fossils date to between 143 and 167 million years ago. Fossils are scarce because snake skeletons are small and fragile.

Pythons and boas are among the more primitive groups and still carry tiny vestigial hind limbs, seen as small claw-like spurs either side of the cloaca. Front limbs are absent in every known snake.

Much of today's snake diversity appeared after the dinosaurs died out. In North America, the grasslands spreading during the Miocene led to a burst of snake variety, including the diversification of colubrids and the origin of genera such as Lampropeltis and Pantherophis.

The oldest preserved written descriptions of snakes are in the Brooklyn Medical Papyrus.

Snakes are ambush predators and can wait a long time between meals. They have lost the hunger hormone ghrelin, which suits these long gaps. After a meal they become inactive while they digest, and when undisturbed digestion is highly efficient, dissolving everything except hair, feathers and claws.

Snakes cannot bite or tear their food to pieces, so they swallow it whole. Their jaws are extremely flexible rather than dislocating, which lets them take prey wider than their own head. Non-venomous snakes often subdue prey by constriction. A snake disturbed soon after eating will often bring its meal back up so it can escape.

They smell by flicking out a forked tongue and passing particles to a organ in the mouth. They are sensitive to vibration and can pick up even soft speech in quiet surroundings. Most can see well enough to track movement. Some snakes, such as boas, also have heat-sensitive pits along the upper lip.

Snakes shed their whole outer skin in one piece, like a sock turned inside out. Before a shed the skin turns grey and the eyes look silvery, then the eyes clear after a few days. Snakes may shed four or five times a year, depending on weather, food supply, age and other factors.

Snakes have a few body-plan features worth knowing. Most have only one working lung, and paired organs such as the kidneys sit one in front of the other. They have a three-chambered heart and no lymph nodes. Their teeth are continually replaced.

Because snakes are ectothermic, their body temperature depends on their surroundings. Too long in direct sun can heat their blood beyond tolerance, and being left in ice or snow may freeze them.

Even non-venomous bites cause tissue damage, as with any animal bite. Sex can be worked out in some species by counting scales and probing the cloaca.

Certain snakes can live for more than 40 years with proper care.

This is general awareness only, not veterinary advice. Always consult a vet about your pet's health.

What is a snake?

A snake is a limbless reptile in the suborder Serpentes, closely related to lizards. It has an elongated body covered in overlapping scales and breathes air.

Are snakes slimy?

No. That is a popular notion, possibly from confusion with worms. Snakeskin is smooth and dry.

Can snakes really dislocate their jaws?

No, this is a popular belief. Their lower jaw is extremely flexible, with the two halves not rigidly joined, plus many extra skull joints, which lets them swallow large prey whole.

Are all snakes venomous?

No, most species are non-venomous. Venomous species use venom mainly to paralyse and kill prey rather than for self-defence. Non-venomous snakes often subdue prey by constriction.

Can snakes hear?

Yes. It was widely believed until the mid-20th century that they could not. They pick up vibrations through the skin and spine, and through the lung to the brain.

How often do snakes shed their skin?

Snakes may shed four or five times a year, depending on weather, food supply and age. The old skin usually comes off in one piece.

Snakes live on every continent except Antarctica, but not on Ireland, Iceland or New Zealand.

Snake skeletons can have between 200 and 400 vertebrae, sometimes more, compared with about 60 in a mouse.

Python embryos grow hind limb buds, but these stop developing before hatching.

Most female pythons coil around their eggs until they hatch, and can shiver to make heat.

The African egg-eating snake has no teeth and can swallow eggs much wider than its head.

Kingsnakes prey on other snakes, including venomous ones, and some have developed resistance to certain venoms.

A snake's old skin can, if intact, theoretically identify the snake that shed it.