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Snakes: Super senses, stretchy jaws and deadly venom
Our planet is home to more than 4,000 species of snake. They live almost everywhere, including here in the UK.
But how much do you really know about these legless reptiles?
Discover why snakes stick their tongues out at you, whether they really dislocate their jaws to eat, how many ways there are to slither and much more.
Where do snakes live?
Snakes have evolved to survive in a huge variety of habitats.
Some live in deserts or dry plains, others are master tree-climbers that thrive in forests, while many spend most of their lives burrowing in soil. Then there are sea snakes, which are adapted to spend most of their lives in the ocean. Anacondas are some of the world’s biggest snakes and they spend lots of time in water too. Their eyes and nostrils have evolved to be on top of their heads – an adaptation that lets them see and breath while keeping the rest of their body submerged.
Snakes live almost everywhere but you won’t find them in the coldest parts of the world, including Antarctica, Greenland and Iceland.
Land snakes are also missing from some warmer island countries, such as Cape Verde, Tuvalu and Kiribati. But these islands aren’t entirely snake-free. Sea kraits sometimes come ashore to lay their eggs. Occasionally non-native species have been found on isolated islands, most likely having been accidentally carried in on boats or in shipping containers.
Arabian sand boas are desert dwellers. Unlike most snakes, their eyes are on top of their heads rather than to the sides. This lets them sit just under the surface of the sand with just their eyes stuck out like little periscopes. © Dan_Koleska/ Shutterstock
Do snakes have bones?
Snakes have lots of bones, but fewer types of bones than us. As well as their skull, they have 100–400 vertebrae in their spine and up to 200 more in their tail. Adjoining from most of these backbones are a pair of ribs that can often move independently of each other.
Movable ribs let many snakes expand their bodies to make room for large food items. Snakes haven’t got a diaphragm, so they also move their ribs to create the changes in pressure needed to breathe. Cobras use their ‘neck’ ribs to flare their iconic hoods too.
Snakes might have more bones than us, but they have fewer types of bones. They only have a skull, vertebrae and ribs.
How do snakes move?
Snakes don’t have arms or legs, so they slither around on their bellies. They mostly rely on friction against irregularities on surfaces, such as rocks, grass or tree bark, to push and pull themselves along. Surfaces where they can’t get traction pose a challenge – a snake would struggle to move well on a super smooth floor, for example.
Most snakes move in a wavelike S-pattern. As they weave side-to-side, they subtly use their loops to push themselves off the ground to move forwards.
Sea snakes and sea kraits undulate in an S-pattern, weaving their way through the water. They propel themselves with flattened, paddle-like tails. © Rich Carey/Shutterstock
Some can also use a concertina-like movement. They anchor one part of their body and then pull or push with their other sections to shunt themselves along. Some snakes use this motion, aided by their flexible skeletons and strong muscles, to help them scale trees with relative ease.
There are snakes that can move in an almost completely straight line – this type of movement is known as rectilinear motion. These snakes anchor their belly scales at several points along their body and use them to very slowly pull the sections in between forwards along the ground.
Then there are sidewinder snakes. These move at an angle, lifting part of their body off the ground while keeping the part in contact with the floor still and pushing left or right. As they pick up and place down their bodies, they leave a discontinuous series of tracks. This style of movement is often used on loose ground, such as sand.
Peringuey’s desert adder is a sidewinding species found on the sand dunes along the Namibian and southern Angolan coasts. © Chantelle Bosch/ Shutterstock
Snakes can’t fly, but some, such as the paradise tree snake, can move from tree to tree by leaping off branches, flattening their bodies and gliding.
Many snakes burrow headfirst in sand or soil, some generating high forces to achieve this.
What do snakes eat?
All snakes are carnivores. Their diets range from large mammals to birds, fish, insects, earthworms, eggs, slugs and snails.
Other carnivores, such as lions, use sharp teeth to tear into animal carcasses. But snakes can’t tear their food or even chew – they don’t have the type of teeth and muscles required for that. Instead, snakes swallow their dinners whole.
Our snake researcher Marion Segall breaks down the myth that snakes dislocate their jaws to eat.
Snakes that eat very large prey don’t unhinge or dislocate their jaws to eat – their mouths are just really stretchy. The lower jaw is made up of two parts that are joined by a ligament. The back of each of these parts is attached to the top of the skull via another mobile joint. This allows the snake to stretch the sides of their lower jaw apart when they need to open their mouth really wide.
Most snakes’ skulls are generally very flexible – they’re made up of approximately 30 bones, some of which can move independently of each another. This lets them ‘walk’ their head up around their dinner to edge it slowly down their throats. Some combine this with backwards-curving teeth that hook into their food and prevent it from slipping back out of their mouth.
Big snakes are known to occasionally eat enormous meals. Among the largest recorded was a 59-kilogramme impala eaten by a 4.87-metre-long African rock python. But they have limits – rangers in the Everglades National Park, USA, once discovered 3.9-metre-long Burmese python that had burst while trying to eat a 1.8-metre alligator.
Man-eating snakes are incredibly rare. Most victims are babies or young children, though a few adults have met this grisly fate too. In recent years, a 25-year-old and a 54-year-old were both swallowed by seven-metre-long pythons in Sulawesi, Indonesia.
Snakes have flexible skulls and super stretchy mouths that help them to swallow large meals. © Butterfly Hunter/ Shutterstock
Are snakes poisonous?
Almost all snakes that produce toxins are venomous rather than poisonous. To get into a victim’s bloodstream, venom enters through a wound, such as a bite or sting. Poison doesn’t – it can be absorbed through the victim’s skin or digestive system, or even inhaled.
Venomous snakes make venom in glands in their heads and deliver it through a bite with needle-like fangs. Vipers and cobras inject their venom through hollow teeth. In other groups of snakes, the teeth can be solid or have a deep groove that acts as a channel for venom. The shape of the fangs varies depending on what the snake prefers eating. Some cobras can also spit their venom considerable distances, often aiming for a threat’s face for maximum damage.
Venom evolved in snakes to help them hunt. Some will use it to defend themselves too. The toxins’ effects typically depend on the type of snake – some venoms damage muscle, others nervous tissue or blood.
Snakes can’t chew to process their food, but in rear-fanged snakes some species will gnaw on their prey, which releases their venom. These toxins may subdue their prey and help with digestion.
Many colubrid snakes don’t pose much of a threat to people. Africa’s boomslangs are one of the exceptions. These rear-fanged snakes can deliver potentially deadly bites. © Travel_photography_Timo/ Shutterstock
There are a few poisonous snakes too. These animals sequester poison or distasteful chemicals from the animals they eat and repurpose them as a deterrent within their own bodies.
One example is the North American garter snake. These eat rough-skinned newts, which have tetrodotoxin in their skin – that’s the same deadly chemical that’s in pufferfish and blue-ringed octopuses. Garter snakes are resistant to tetrodotoxin’s effects and will harbour the chemical in their own bodies in amounts that could kill or incapacitate their own predators.
Some keelback snakes sit on both sides of the fence, using poison they sequester from toads as a venom. The toad poison is absorbed into the snake’s blood, then secreted through their salivary glands and delivered through a bite.
Are snakes blind?
Most snakes have specialised, almost transparent scales called spectacles covering their eyes, but they can still see. Unlike most of their lizard relatives, snakes don’t have eyelids. In fact, in the UK, blinking is one of the clues that helps us tell slow worms – a type of limbless lizard – and snakes apart.
A snake’s vision matches its lifestyle and can be quite important. For example, some species have very large eyes, and some have evolved ultraviolet-blocking lenses that help them to see clearly and hunt in bright sunlight.
But eyes aren’t the only organs that help a snake catch its dinner. Some have nerve endings in specialised pits in their faces that let them ‘see’ into the infrared spectrum and pick up heat signals from prey. This can help them hunt in the dark.
Some snakes have pit organs that let them sense infrared radiation. These can look like a series of holes in the snake’s face. © Maris Grunskis/ Shutterstock
Chemical sensing is generally important to snakes, sometimes more so than eyesight. Snakes have forked tongues that they flick in and out of their mouths. By sticking their tongue out, they pick up odour molecules from their environment. When they retract their tongue, the molecules pass into the vomeronasal organ in the roof of their mouth, delivering smell information to the brain.
Do snakes have ears?
Snakes don’t have an external opening to their ear or eardrums, but they do have the same parts of the middle and inner ear that we do. Although they lack outer eardrums, they can still hear via vibrations transmitted through the body and head. The inner ear also helps with their sense of balance.
Why do snakes shed their skin?
Snakes are covered in scaly skin made of keratin that can be very colourful and even iridescent. Scales are tough and help protect the snake from damage from its environment, predators and feisty prey. They can also act as a barrier that reduces the loss of water.
Snakes regularly moult to allow for growth, repair damage and remove parasites. They grow a new layer of skin under the old one and then secret fluid between the two. The snake then breaks through the old skin and works its way out of it, revealing the new, polished skin.
Some snakes have smooth scales. Others, such as this Eastern diamondback rattlesnake, have keeled scales, which have a ridge down the centre. Their rattles are made up of modified, hollow scales. © Chase D'animulls/ Shutterstock
Snakes’ scales vary in size and shape depending on where on the body they are, the species and their lifestyle.
Rattlesnakes, for example, have modified scales at the end of their tails that form a set of interlocking segments. They vibrate these to create a rattling sound as a warning to nearby threats. In contrast, the spider-tailed horned viper uses its tail as a lure – it’s shaped like a spider to attract the snake’s next meal.
Some snakes are camouflaged, using the colours and patterns of their scales to blend in with their environment.
Others use bright colours as a warning to predators. Venomous Eastern coral snakes, for example, feature bold bands of black, red and yellow. Some less dangerous snakes have evolved patterns similar to those of dangerous species as a deceptive self-defence tactic – this is known as Batesian mimicry. Scarlet kingsnakes are well known, harmless mimics of Eastern coral snakes, for example.
Eastern coral snakes use bright colours to tell threats to keep their distance. This is known as aposematism. © Patrick K. Campbell/ Shutterstock
Are snakes endangered?
The International Union for Conservation of Nature lists more than 120 species of snake as Endangered or Critically Endangered.
Emerging diseases, such as snake fungal disease, caused by the fungus Ophidiomyces ophiodiicola, are among the threats. Some scientists have drawn cautionary parallels between this disease’s sometimes-fatal infections and the devastating spread of chytridiomycosis in amphibians.
But it’s people that are at the root of many of snakes’ problems. The threats we pose include habitat destruction through agricultural expansion, resource extraction and building, as well as through the effects of climate change.
Some snakes are also harvested by people as a source of exotic meat, as well as for their skin, which is turned into leather.
In some places, rattlesnakes are intentionally persecuted in recreational ‘round-ups’. These grisly festivals are dedicated to capturing, beheading and skinning the reptiles, sometimes under the guise of promoting awareness and safety around wild venomous snakes.
Our actions threaten snakes’ ability to survive and can alter their distributions, bringing them into contact and conflict with people more often.
In the UK, our snakes and other reptiles are protected by the Countryside and Wildlife Act 1981, which makes it illegal to kill or injure them. Discover which snakes you might be lucky enough to spot out and about in the UK and how to identify them.
