What is a Snake? A Simple Plan

All snakes have a simple form—a head, long body, and tail. A snake is really just a tube of bone and muscle wrapped around internal organs. The relationship between muscles, ribs, and vertebrae give the body incredible strength and flexibility. Body shapes and lengths of snakes vary. Some ground dwelling snakes tend to have thick, short bodies with obvious tails. Tree snakes tend to be long, thin, and very light—much better for climbing trees! The shortest species known is the thread snake from the West Indies, only three inches long fully grown. The longest species is the reticulated python from Southeast Asia, which can grow up to 32 feet in length.

Anatomy

They're So Cool. Snakes are "cold-blooded ectotherms," which means their body temperature changes with the temperature of their environment. They depend on their surroundings for warmth. In contrast, birds and mammals, including humans, maintain their body temperature regardless of their surroundings. The tropics have far more snakes than any other region on earth because it is easier for them to keep warm in constantly hot weather. Cold severely dulls a snake's senses and slows its movements, preventing it from living in extremely cold habitats. They can survive in changing habitats like Indiana by basking in the sun to raise their body heat or by hiding in the shade to cool down.  Photo by Fred Cate

A Ribbon of Bone

Because a snake has no arms or legs, its skeleton consists mainly of a skull, backbone, and ribs.  The backbone has hundreds of vertebrae, each connected to a pair of ribs that gives the snake's body great flexibility.  The small "wings" on each vertebra limit how much the spine can twist without damaging the spinal cord.  A snake's skeleton is also designed to allow it to swallow prey much larger than itself.  Loosely attached jaws, expanding ribs, and no breastbone enable snakes to swallow large prey. 

Scales From Head to Tail

Like all reptiles, snakes are covered in overlapping dry scales.  Their eyes are covered by clear, bubble-like scales called spectacles.  Scales give the skin remarkable flexibility, allowing the body to stretch in order to swallow surprisingly large prey.  Scales act as a type of "armor" that protects snakes from wear and tear, drying out, and damage by predators.  Scales contain pigments that give snakes their colors and patterns.

Making Sense of the World

Like all animals, snakes depend on their senses to help them get around, find food, avoid enemies, and even find a mate.  Unlike us, snakes rely much more on smell and touch than on sight and hearing.  Smell is a snake's most important sense.  Although it can smell through its nose, a snake also uses its ever-moving forked tongue to locate prey and find its way. Odors are sampled by flicking out the tongue and retracting it across a special organ in the mouth called a Jacobson's organ, which detects and analyzes the molecules chemically. Touch is a vital sense for survival.  Many snakes' scales are highly sensitive to touch and to picking up vibrations from the ground.  Sight is a most unique sense of "vision."  Although most snakes can see, some species have better vision than do others, and it is doubtful that any snake can see in color.  Some snakes can "see" in ways that we can't—in the infrared spectrum.  Special "heat pits" on their heads detect infrared radiation given off by warm-blooded prey. Hearing is a significant, but less-used sense.  Although snakes have no external ears, they are not deaf.  They can detect airborne sounds in a limited range, though they probably rely on hearing less than other senses. 

Locomotion - On the Move

They may not have legs, but snakes move quite well.  They can navigate on land, in water, and even in the air.  Some snakes, like certain desert species, can only move in one manner.  Most species can switch from one type of movement to another as the surface requires.  Movement styles include:  serpentine ("s-shaped"), rectilinear ("caterpillar style"), sidewinding ("rolling spring"), concertine ("accordion style").   Scales also allow snakes to move.  Most snakes push their large belly scales along uneven surfaces, thereby moving their bodies forward in a series of waves.

Reproduction - Starting Out

Snakes reproduce either by laying eggs or giving live birth. Egg-laying species lay leathery eggs, often in rotting leaves or in old logs, where they can be kept moist and warm.  Newborn snakes hatch by cutting through the eggshell with their sharp eggtooth, which is lost soon after birth. Live birth means that the babies come out of their mother fully formed and ready to face the world.  Technically, the young simply hatch from eggs inside the mother.  Then they are born.  Live birth is often seen in snakes that live in water or in trees where there may not be a good place to lay eggs.  Snakes do not require prenatal care as mammals do.  At birth, snakes are ready to take care of themselves.  Most, but not all, female snakes abandon their eggs once they are laid.  Female thread snakes, certain pythons, and king cobras have been seen protecting their eggs. 

Feeding Strategies - What's for Dinner?

All snakes are meat eaters and all have developed clever ways to catch and kill other animals.  Species that feed on small prey usually grasp the prey in their jaws and swallow it whole (and often alive).  Snakes that eat larger and potentially more dangerous prey must kill it before eating.  Many snakes such as boas and pythons kill by squeezing and constricting their prey.  When a snake's powerful coils wrap around an animal, its lungs get compressed and it dies.  Some snakes inject venom into an animal to kill it.  Venoms differ but generally kill by affecting the nervous system, tissues, or blood (or all three).  Less than one-fourth of all snake species are venomous.

Defense Strategies - Avoiding an Enemy

Snakes are both predator and prey. They have many natural enemies, including spiders, birds, mammals (including humans), other snakes and even insects!  Many snakes have died at the hands of humans, whether through direct killing or through habitat change.  Snakes evade enemies through various strategies.  The most common defense is to keep from being seen, since it reduces the need to fight.  That's why snakes spend most of their time hiding, aided by colors and patterns that camouflage them or serve as warnings to potential enemies. Most snakes try to flee when threatened.  If this strategy doesn't work, they have a variety of behaviors to ward off attackers.Cobras try to intimidate their opponents by "hooding up" in a threatening posture, and rattlesnakes shake their tails to warn of their presence.  Usually snakes attack only as a last resort. 

Habitat -   Where They Live

Snakes live in almost every part of the world except the poles and mountain top ranges.  They are found in deserts and rainforests as well as in salt and fresh water.  Some snakes burrow under the ground while others hang around the tops of the highest trees.  They are even found in cities.  Snakes are most numerous in tropical climates around the equator, where warm temperatures allow them to be active all year.  Like all reptiles, snakes face one main limitation in their ability to live in all habitats- they are "cold-blooded", and thus cannot tolerate the cold.  Snakes have developed a number of strategies, however, for surviving in cold and unpredictable weather. 

Snakes and People -   Our Quiet Neighbors

Snakes live right beside us in Indiana.  While that fact may be scary to some people, these quiet reptiles can be good neighbors.  Snakes play an important role in nature.  They eat numerous rodents and insects that can cause crop damage and disease.  There are times, of course, when snakes and humans come into conflict.  Sometimes snakes seek shelter near people's houses, decks, or tents.  Hikers may startle a basking snake on a trail.  Usually these encounters end peacefully.  Snakes are shy, and if left alone, will flee rather than attack.  If provoked, however, a snake may bite to defend itself.  Like all wild animals, snakes deserve a healthy respect.  There is no "bad" or "good" in nature.  Snakes are among the many creatures that play a critical role in the natural world.  Removing them from their environment would harm the entire ecosystem and would deprive us of some of the most fascinating animals on Earth.   

Friend or Foe?

Culture, religion, mythology, and misinformation influence our beliefs about snakes.  Some people revere them, some people loathe them, while others regard them as mystical messengers.  Snakes are misunderstood, but one thing is for certain—people have strong beliefs and feelings about snakes.  Perhaps these beliefs are the basis for many of our misconceptions and fears about these reptiles.  Snakes play an important role in our natural environment.  While some snakes, especially venomous ones, have posed problems for humans, these animals also control pests that eat crops and spread disease.  The biggest threats to snakes worldwide include habitat destruction and trade in wildlife products such as medicine, boots, bags, and belts.  Some snake species have been brought to the brink of extinction, often before we knew enough to save them.