SNAKES, THEIR HISTORY, SENSES, MOVEMENT, ANATOMY AND HUNTING AND FEEDING BEHAVIOR

SNAKES

There are approximately 2,700 species of snake, ranging in size from pencil-size African thread snakes to 25-foot anacondas large enough to swallow a human child. They live in almost every ecological niche, except the polar regions, and are particularly plentiful in tropical regions and deserts. [Source: Adrian Forsyth, Smithsonian, February 1988; Frederick Golden, Time magazine, October 13, 1997]

Colubrids, sometimes referred to as typical snakes, are the largest snake family, accounting for almost two thirds of all species. Common features among colubrids include a lack of a left lung, and backlimb girdel. Garter snakes, grass snakes, whip snakes and all rear-fanged venomous snakes are Colubrids. Colubrids are regarded as more developed than primitive blind snakes, thread snakes, and boas and pythons. Most dangerous venomous snakes are not Colubrids. They are front-fanged snakes.

Among reptiles, snakes are most closely related to monitor lizards and Gila monsters. All these creatures have forked tongues and sense organs on the roofs of their mouth.

Some snakes are easily killed by prolonged shelter to the sun that is why they often seek shade in the middle of the day. In temperate climates many snakes hibernate for three or four months in the winter: they don’t eat that entire time yet emerge at about the same weight as when they started. In some places some species gather in large numbers and live in the same den, which they return to year after year.

Websites and Resources on Animals: ARKive arkive.org Animal Info animalinfo.org ; Animal Picture Archives (do a Search for the Animal Species You Want) animalpicturesarchive ; BBC Animals Finder bbc.co.uk/nature/animals ; Animal Diversity Web animaldiversity.ummz.umich.edu ; International Field Guides media.library.uiuc.edu ; animals.com animals.com/tags/animals-z ; Encyclopedia of Life eol.org ; World Wildlife Fund (WWF) worldwildlife.org ; National Geographic National Geographic ; Animal Planet animal.discovery.com ; Wikipedia article on Animals Wikipedia ; Animals.com animals.com ; Endangered Animals iucnredlist.org ; Endangered Species Resource List ucblibraries.colorado.edu ; Biodiversity Heritage Library biodiversitylibrary.org

Websites and Resources on Reptiles: Reptile Database reptile-database.org ; Reptileweb reptilesweb.com ; Reptile Channel reptilechannel.com/reptile-species ; Wikipedia article Wikipedia ; Reptile Phylogeny whozoo.org/herps/herpphylogeny

Websites and Resources on Snakes: Snakes Pictures and Info freesnake.com ; Snake World snakesworld.info ; Venom Center Venomous Snakes venom-center.com ; Ten Most Poisonous Snakes kalyan-city.blogspot.com/2008 ; National Geographic snake pictures National Geographic ; BBC Snakes bbc.co.uk/nature/life/Snake ; Snaketracks.com snaketracks.com/index ; Wikipedia article Wikipedia ; Snake Species List snaketracks.com ; Snakes of India Photos naturemagics.com ; Herpetology Database artedi.nrm.se/nrmherps ; Snake Resource List 42explore.com/snake ; Types of Snakes buzzle.com/articles/types-of-snakes ; Big Snakes reptileknowledge.com ; Venemous Snakes venomoussnakes.net ;

Snake History

Snakes most likely evolved about 90 million years ago from lizards that took to living underground or in forest litter and lost the use of their legs. Evidence of this includes the snake's lack of an eardrum (underground animals generally have no use for hearing) and the remnant of leg and pelvic bones still found in many snakes. Pythons, for example, have tiny leg bones which may be visible as minuscule claws at the base of their tails.

But the matter of how snakes evolved is far from settled. For some time there has been a debate on whether the first snakes evolved on land or in the sea. Some think they evolved from monsaurs, an extinct group of large marine reptiles. Even if this case it clear from anatomical evidence that modern aquatic snakes descended from terrestrial snakes.

In April 2006, scientists, announced the discovery of the oldest known snake in Patagonia. Measuring less than a meter in length and given the name Najash rionegrina, the fossil back up the case that snakes evolved on land. The skeleton contains a bone structure that support the pelvis, a feature lost by sea creature long before, two small rear legs and anatomical features suggesting that it lived in burrows. The deposits in which it was found also indicate it came from a terrestrial environment. The creature likely moved around like a snake. The purpose of the two legs is unknown.

In February 2009, Jonathan Block, a vertebrate paleontologist at the University of Florida, announced the discovery of a fossil of the most enormous snake ever found: a giant boalike snake that lived 60 million years ago that was as long as a bus and large enough to eat crocodiles and 150-kilogram giant turtles. Based on the size of it vertebrae the creature weighed between 730 kilograms and two tons and measures between 11 and 15 meters and was more than 1.25 meters wide at is widest point. The fossil was found in one of the world’s largest open cast coal mine in Cerrejon, Columbia.

Block told AFP, “Truly enormous snakes really spark people’s imagination but reality has exceeded the fantasies of Hollywood. The snake that tried to eat Jennifer Lopez in the movie Anaconda is not as big as the one we found.

Snake Characteristics

A snake's internal organ have been shrunken, stacked on top of one another and ingeniously engineered to fit in their body. Their skeleton consists of flexible backbones and dozens of pairs of ribs. Their skins is covered by scales and is generally dry to the touch.

Most snakes have only one lung. It is exceptionally long, reaching well into the snake’s body. When the lung is full of air it looks almost as if the snake has swallowed another snake. Snakes lack a diaphragm muscle to push their lungs. Their rib muscles which expand the chest during each breath also propel the body forward when the snake moves.

Snake scales don't grow so the skin has to be shed when the snake gets bigger. Snakes shed their skin several times a year. Before this occurs their skin color is dull and their eyes are milk colored. Snakes are partially blind at this time and usually try to stay hidden. A couple of days before the shedding begins, the color returns to the skin and eyes. An oily secretion collects under the old skin and loosens it, and the skin cracks at the lips. The snake rolls back the skin, often with the help of a rock, and begins crawling out, rolling the skin inside out like a glove as it moves out. The eyes covers are shed along with the skin.

The skins from cobras, pythons, lizards, water snakes and other snakes has a beautiful texture and patterns. They are used to make expensive shoes, handbags, luggage, belts and garments. The bright colors found on some poisonous snakes is a warning to potential predators that the snake is dangerous to them. Some non-poisonous snakes have patterns that mimic poisonous snakes , which are intended to scare off predators.

Occasionally you get bright blue rattlesnakes due to a genetic defect.

Some snakes dig burrows. Most of those that do---along with other legless creatures that dig burrows---usually rely on their heads to excavate or compact earth. The eastern hognose snake has a protuberance on its head that helps it scrape away the soil and compact it upwards, The Louisiana pine snake loosens sand and soil with its “nose” and “hoes” it out by bending its head downward. The shield nose cobra move sits head from side to side, scraping the soil and with its flat shield, the Saharan pit viper buries itself by flexing its side and twisting to scoop out sand. [Source: Natural History, December 2006]

Snake Senses

Snakes have keen senses of smell, temperature and touch but generally have poor eyesight (except night snakes that have catlike eyes). Snakes don't have movable eyelids, and consequently they can not blink. Their eyes are covered and protected by transparent scale called a braille.

Lizards and snakes are both very good at sensing and analyzing smells and message-carrying chemicals Many have a vomeronasal organ embedded in the roof of their mouth that detects heavy non-airborne molecules taken in through the mouth. It supplements olfaction which is the ability to smell airborne molecules that enter the nostrils and is distinct from taste, which analyzes chemicals that come into contact with taste buds on the tongue. These senses help reptiles locate prey and help warn them or potential prey that might be toxic. It also frees up the eyes to locate prey and find mates.

The vomeronasal organ is sometimes called the Jacobsen's organs. Lizards and snakes with forked tongues have these on either side of the roof of their mouth. Chemicals are picked up from the environment with their forked tongues then transfer to these organs.

Lizards and snakes with forked tongues constantly flick their tongues in and out of their mouths, bringing in new samples of chemicals on either side of the tongue through the chemical equivalent of stereoscopic vision. Not only can they determine the presence of chemicals they can also determine the direction which they are coming from and detect edges and dimensions of the sources.

Lizards and snakes use their forked tongues and sense organs in their mouth to locate food, enemies and mates. And this they can do without even opening their mouths. Predators rely on smells and message-carrying chemicals to locate their prey and use their eyes to determine the location of the prey for the final lunge.

Unlike lizards, snakes don't hear very well. They lack eardrums external ears, which are believed to have been lost from when they first evolved underground from burrowing reptiles millions of years ago. They have retained some of their ear bones and can sense vibrations through their jaws. The only vocal sounds that most snakes make are hisses. Some growl. Snakes of all species shake their tails when agitated, but only rattlesnakes can make a noise with their tails. Some species of snake play dead when they sense danger.

Rattlesnakes, pit vipers and other snakes have heat-sensitive, infra-red-detecting facial pits that allow them to detect prey several meters away. Information from the pits and eyes is processed in same area of the brain, allowing the snakes to “see the body heat of an animal perhaps as a brighter image.” Some animals have built in defenses against a rattlesnakes heat sensing capabilities. Ground squirrels keep their tail cool when they sense most kinds of snakes. But if a rattlesnake comes near they heat up their tails and furiously move them from side to side---a process called tail wagging---to thwart an attack.

See Lizard Senses

Snake Movement

The skeleton of a snake is essentially a skull connected to a long spinal columns and rib cage. Most of the muscles run longitudinally between the vertebrae and the ribs. Some are short connecting one rib to another. Other are longer, spanning as many as 40 vertebrae. When muscles are contracted they move close together, causing a section of snake to curve.

Snakes move forward by making their skin crawl. Most snakes have horny, backward-pointing plates on the undersides of their bodies that overlap and grip the ground. Muscular movements within the body move the snake forward.

Snakes move by producing alternating waves of muscles contractions. Describing this movement, David Attenborough wrote: "They flex their flank muscles in alternate bands so that their body is drawn into a series of S-shaped curves. As the contractions ravel in waves down their body, their flanks are pressed against obstacles on the ground such as stones or plant stems and the snake is able to push itself forward. In short it wriggles. If it is put on a surface completely free of any irregularities...the technique fails and the snake simply writhes helplessly."

When hunting, it is very important for snakes to move quietly and with a minimum of movement so as not to alert its prey. Under these circumstances, the snake approaches the prey straight on, keeping its is head still, body straight and slowly moving forward by using contracting muscles on its belly.

A striking snake arches its body near its head to for form an "S" and then straightens out its body. A completely snake can not strike. A striking snake an generally only strike out half a body length

Many snakes are good climbers, using the scales on their undersides to grip on to on bark, or winding themselves around branches. In the rain forest you are more likely to find snake sin the trees than on the ground. Many snakes are also good swimmers They can inflate their lung to float on the top of the water an use their belly scales to grip the surface of the water and slide across the water almost as easily as they do on land.

Snake Breeding

Male snakes have two sex organs (called hemipenises) hidden behind a flap at the base of their tails. Some species use them alternatively in quick, successive couplings or gang-bang orgies. Others favor one hemipenis in long copulation that deters rivals.

The Brahminy blind snake is a snake species with no males. Females lay their eggs without having them fertilized by a mate. The snakes habit of hiding away in potted plants has enabled to spread all over the world.

Female snakes sometimes store sperm inside their bodies for several months until a climate change signals the snake it is the right time to start fertilization. Pregnant females are sometimes unable to feed during the later part of their pregnancy and go months without feeding, relying on fat stored in their bodies.

Most snakes lay eggs but some give birth to live young that hatched from eggs inside the female snake's body. Snake eggs usually have a soft, flexible, non-brittle shell. The young are born encased in a membrane that breaks. Some species lay their eggs among rotting leaves or logs to keep them warm. The eggs can take several days to several months to hatch. The determining factor as to when they hatch is hot the weather is.

Depending in the species, snakes lay between 2 and 100 eggs with most species laying between seven and nine. Young snakes have a special scale at the end of their end of their nose call the egg tooth which they use to break out of their leathery shells.

Snake Hunting and Feeding Behavior

All snakes are carnivorous and they prefer live prey. They often rely on stealth to capture prey and swallow it whole. Small species eat insects, worms, slugs, scorpions and frog's eggs. Medium size ones eat mice, baby birds, eggs, frogs, fish and other small animals. Large snakes can eat small mammals, other snakes, birds, and even babies. Some species can consume prey that is two and half times their body weight.

Snakes rarely eat more than once a week, unless their prey is really small. On average a snake takes 12 to 14 days to digest a meal, and it is not unusual for a snake to go several months without eating After a big meal some snakes remain inactive for several days while it digests its prey. If a snake is threatened it sometimes regurgitates its meal so it can escape more quickly.

Many snakes to laze around and hang out in places their prey is most likely to pass, stalk their prey when it gets near and get close enough to strike. Many snakes have camouflage markings and an ability to stay very still so they are not detected. Many can catch their prey with a single strike. Some species specialize in going into the holes of burrowing animals. Many climbing snakes seek out nests and feed on eggs and chicks. A few species use their tails as lure prey which mistake the tail for a worm or caterpillar

Snakes that feed on large, potentially-dangerous creatures kill them first, usually by poisoning or through constriction. Large prey is swallowed head first. Otherwise the legs might get caught up in the snake’s throat. The insides of the snake clamp down on the prey, preventing it from moving or opening its mouth to damage the inside of the snake.

Everything but hair and feathers is digested. Some snakes that primarily eat eggs swallow the eggs whole and a sharp objects in their gullets break the shell, which is when spit out. Many snakes can go months or years without drinking, instead getting the water they need from their food. Those that do drink stick their heads under water and use their jaws to pump water into their body or suck water from wet leaves.

Snake Feeding Anatomy

Snakes are unable to dismember their prey and must swallow it whole. They have a lower jaw bone that is divided in half and hinged with ligament that stretches sideways. The bones supporting the lower jaw on the skull are movable so the mouth can open very wide. These things allow snakes to swallow food that is larger than themselves.

Snakes are able to breath and not choke when they swallow large prey because their windpipe extends almost to the end of their mouth and they have special muscles that pull the windpipe opening forward past the prey as it is being swallowed.

The fangs and teeth of most snakes point backwards which helps force large prey towards the throat and keep even slippery creatures such as frogs from slipping back out. Snakes move prey into their gullet by alternately moving the right and left sides of their jaws, Depending on the size of the prey the process can take from a few seconds to a few hours but generally takes a few minutes.

Rippling muscles inside the snake move the prey towards the stomach. Sometimes the prey remains alive while it moves through the snake’s throat. The prey of poisonous snakes often dissolved from the inside out inside the snake.

In order to swallow many snakes crawl over their food by contracting their muscles, pushing their bodies on the ground and their prey inside their bodies at the same time. Some snakes rotate their jaw forward, then pull it backwards, and "walk" their head over the victims. Snail eating snakes rotate their jaws in such a way that they hook the snake and pull it from the shell.

Suffocating Snakes

Snakes like boa constrictors and pythons seize their prey with their mouths, and wrap their coils around it so the prey can no longer expand its chest and breath. They kill through suffocation rather than crushing or choking.

Often something more than mere suffocation is also going on. A suffocated rat, for example, usually dies in four minutes. A rat killed by a constricting snake dies in one minute. Studies indicate that snakes disrupt the circulation of their victims, doubling their victims’ blood pressure so that heart can not pump sufficient blood to the brain, lungs and other tissues, killing with a heart attack or stroke.

Pythons can eat animals half their weight. They have been observed swallowing leopards and impala, sometimes stretching their victims as they swallow it. The diameter of their prey is usually the limiting factor. Generally though pythons avoid extremely large prey because they become grotesquely distended and have great difficulty moving and become vulnerable attacks by other predators such as crocodiles or humans. When they are distended like this and need to make a quick escape they can regurgitate their meal.

Pythons move very quietly and often are able to capture prey by sneaking up quietly on it. They mostly eat small birds or mammals which they surprise with their stealth. Pythons hunt both day and night and sense their prey using their facial pits. They seize their victims with their back-curved teeth and vice-like mouths, then wrap the animal in a suffocating embrace, and finally swallow it whole. They sometimes regurgitate the bones of their victims.

A man named Laba told the Blair brothers a story about huge python that dropped on top of him from a tree. "Flattening him to the ground and knocking the wind out of him," Blair wrote, "it had begun the killing process by throwing a few coils around the tree to anchor itself, and a few more around Laba, pinning his arms to his side. It doesn't squeeze very hard, Laba explained, but tightens its grip each time you exhale, making it increasingly harder to draw the next breath. It made no attempt to bite, but held its face close to Laba's, intently watching him while its forked tongue flickered around his nose." [Source: "Ring of Fire" by Lawrence and Lorne Blair, Bantam Books, New York]

"'They look at you very closely,' he told us. It was at this point that Laba had effected the only feasible escape...In the coils adjacent to his wrists he located the python's cloaca and managed to give it one hell of a goosing. The astonished reptile loosened its grip just long enough for Laba to break free and stagger off down the track---with the serpent in hot pursuit...loudly vocalizing...sibilant barks."

Image Sources:

Text Sources: Mostly National Geographic articles. Also Life on Earth by David Attenborough (Princeton University Press), New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

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© 2009 Jeffrey Hays

Last updated March 2011

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