"In the withering heat of the Australian desert the Pierce snake hunts for prey" "It carries in its armament less than two-thousandth of an ounce of venom with a potency that could kill a quarter of a million mice" "Why this snake needs the animal equivalent of an atom bomb in its mouth no one really knows" "But without the limbs and paws of other predators snakes have had to find other ways to be sure of a kill" "Snakes have been around for more than a hundred million years longer than modern humans" "Except for the polar regions and a few islands they have spread throughout the world" "Religion has endowed snakes with mystical powers invoking human emotions from reverence to outright fear" "Snakes live among us" "Yet we find it difficult to accept their presence near our homes whether we see them or not" "This corn snake, however, is totally harmless" "Although all snakes have the same fundamental body plan there are wide variations on the theme" "Measuring up to twenty-nine feet in length the green anaconda is almost ten times longer than the typical corn snake" "And at four hundred forty pounds it is seven thousand times heavier than the blind snake which belongs to the family that includes the smallest snake in the world" "There are around two thousand seven hundred different species of snakes" "Seventy percent of them hatch from eggs" "Others are born live after struggling to break free from a membranous egg sac" "Venom and fangs are found in only a quarter of all known snakes" "But all species have methods of attack and defense that are adapted to habitats ranging from rain forest to desert" "This is the tail of the cantle snake" "Or if you are a frog, it is a worm" "But not for long" "Once tempted, the frog is turned from predator to prey in a single pounce" "Snakes live by stealth, speed and sheer power" "From the tops of trees to the depths of oceans snakes have turned an apparent disadvantage into an evolutionary success" "Creatures without limbs they are the surprise and sometimes fearsome survivors" "In the realm of the senses, snakes seem particularly ill-equipped" "This cobra is not actually hypnotized by the snake-charmer music" "In fact, it cannot hear it like us at all" "Lacking an external ear and with a poorly-developed middle ear it picks up vibrations only if its lower jaw is in contact with the ground" "And with relatively poor eyesight, the cobra fixes its gaze on movement" "In pit vipers, like the rattlesnake vision is supplemented by two concave heat sensors just below the eyes" "These so-called pits are lined with tiny receptor cells sensitive to changes in temperature of two thousandth of a degree Fahrenheit" "In its desert habitat a rattlesnake can tell the difference between a warm breeze and the heat given off by its potential prey" "The brain takes this information and combines it with visual images to precisely locate its prey" "It is so accurate it will have a near-one hundred percent success rate when it strikes" "The importance of sight varies enormously between snake species" "The blind snake has a degenerated eye just a light-receptive cell" "The eyes of many nocturnal snakes are so sensitive that they can track the iris to a slit during the day" "Most snakes are unable to focus their eyes the way humans do" "Instead, they move the lens in and out like a camera" "The long-nosed tree snake is the only snake that can focus by changing the shape of its lens" "It can also see in 3-D" "The uniquely-grooved skull allows the snake's eyes to converge forward" "Snakes can taste air, and the odors it carries" "A specialized apparatus called the acobson's organ is found in all reptiles" "In snakes, the twin tips of the tongue pull scent molecules from the air and deposit them into the organ, passing information to the brain" "So despite its relatively poor vision a corn snake's Jacobson's organ allows it to track a mouse with rapid flicks of the tongue" "For the green anaconda, the hunting tools are the same" "It is the prey that varies" "A mouse would hardly satisiy a twenty-nine foot anaconda" "But a dwarf caiman might" "This relative of the alligator is an imposing challenge" "The anaconda is not deterred" "Relying on its immense strength the anaconda squeezes the life out of its helpless prey" "But how is it possible for a snake to devour an animal that is larger than its mouth?" "An early development in the evolution of snakes was the reconstruction of their heads" "The jawbones and skull became held together by elastic ligaments rather than fixed tightly to one another" "This enabled snakes to widen their jaws and expand the capacity of their mouths" "They also divided the jaw at the chin allowing it to separate and open further" "They use their backward-pointing teeth to grip their prey rather than chew or tear like other predators" "A more recent advance in the evolutionary story of snakes is the development of fangs" "Just a quarter of all snake species devised enlarged teeth with a groove or hollow tube through the middle similar to a hypodermic needle" "They could now deliver venom" "Venom is produced by modified salivary glands found in the top of the snake's mouth" "A mixture of proteins venom can destroy tissue or attack nerve and muscle function" "As this Gaboon viper strikes the dying rats heart pumps venom around its body" "The snake can now wait and track down the dead rat using its Jacobson's organ" "The king cobra is the world's largest venomous snake growing to over sixteen feet" "It preys mostly on other snakes, even venomous ones" "The mangrove snake delivers a mild venom through a set of small fangs toward the back of its mouth" "The cobra, however injects its potent venom with fangs toward the front of its mouth" "Although small in comparison to the Gaboon viper's inch-long fangs the king cobra are no less effective" "As it strikes, the cobra holds on tight ensuring the venom finds its mark" "Within minutes, the mangrove is dead" "Around twenty-five thousand people a year die from snake bites mostly in third world countries, where anti-venom is rare" "Dean Ripa is lucky" "He survived an attack by one of the most venomous snakes in the Americas" "A bite from a bushmaster has an eighty percent fatality rate even with anti-venom" ""You feel a great deal of immediate pain" "It is like a pair of hot needles um, com... combined with vise..."" ""...ah, and a burning sensation." "Ah, this pain has been compared to burn by fire and is one of the the most, ah, ah, terrible pains you can endure as it begins to spread because you feel actually the, the poisons moving up your arm" "You can feel this, this, the swelling increase."" ""If it struck a vein or an artery you may be unconscious within a few minutes" "I was unconscious in seven."" ""Rapid loss of blood, blood pressure" "No heartbeat, ah, to speak of, ah, or a pulse that could be detected" "And it was just a gradual blackening, darkening after that."" ""Um, nada!" "Nada, nada, nada."" "Snakes are rarely aggressive and bites to humans are either accidental or defensive" "Most snakes would rather warn large mammals of their presence" "But some heavy-limbed creatures fail to heed the signals" "A strike is the last resort" "Snakes with venom that mostly destroys tissue can cause devastating injuries on human limbs" "But deaths from what are considered dangerous snakes are still quite rare" ""Want to have a look at it?"" ""Wow." "Now, this is the, what, which type did you say it was?"" "Herpetologist Harry Greene is working to dispel the myth of snakes as murderous monsters" ""Snake bite is wildly exaggerated as a public health problem in the United States."" ""We think probably a thousand people" ", perhaps more, are bitten every year in the United States of which probably fewer than ten people per year actually die" "In the, in the US snake bite is mainly a problem of people handling snakes intentionally or of people just not being careful outdoors."" ""And it is kind of amazing how hysterical we can get about this perceived public health problem and, to the point of, of wanting to kill snakes everywhere and and, and that is the thing with snakes" "If you just remember to not stick your hands in places where you cannot see you will never get hurt."" "Snakes are not just predators" "They are prey, and have inventive ways of defense" "This red-spitting cobra projects venom towards its attacker's eyes" "A cape cobra cannot spit, but it can play a game of illusion" "Sometimes, however, it turns into a game of double bluff" "In South Africa, meerkats prey on small snakes but will take on a cobra to defend their young" "The cape cobra spreads its hood to make itself appear larger than it really is" "The meerkats group together to appear as one large animal to the snake" "This time, the confrontation ends in a stalemate" "The venomous saw-scaled viper ranges over Africa and parts of Asia in areas of dense human population" "It warns of its deadly presence by rubbing together deeply-ridged scales on the side of its body" "But how do you defend yourself if you are a harmless snake?" "You appear to be what you are not" ""One of the neat things about snakes is that with such a simplified body form it is easier for them to to look like something else with relatively minor changes."" ""This is a diadem rat snake from the Middle East that looks and sounds a lot like saw-scale viper."" ""Now this is an absolutely harmless snake."" ""You just saw him bite my knuckle there and nothing bad happened to me" "It is making the sound by hissing" "And the saw-scale viper makes the same sound by rubbing its scales together" "It is a really nice example of mimicry" "If I were in the Middle East and I heard this thing hissing," "I would probably jump back because there would be the possibility that it is a saw-scale viper an extremely dangerous animal."" "These are the colors of danger." "They belong to the poisonous coral snake" "But this snake, the tantilla, has similar color markings" "The coral snake, however, sees through the disguise" "Other snakes are better mimics" "These colors belong to a group of snakes known as the false corals" "As near-perfect replicas they are much more likely to fool predators, some of the time" "As the old American saying goes, red to black, venom lack" "Red to yellow, kills a fellow."" "All twenty-seven hundred or so snake species of today are descended from one common ancestor" "Unfortunately, the fossil record is so poor that little is known about the details of snake evolution" "Some of the best clues lies in the evidence of the present-day rather than the fragmented remains of the past" "Consider the bushmaster" "Although he barely survived a bushmaster's bite" "Dean Ripa continues to collect and study this rarest of snakes" "Until recently the scarcity of the bushmaster meant that it was poorly understood" ""One problem that the zoos have had is trying to obtain good specimens and ah, that is kind of where..."" ""..." "I came in and how I fin... found myself collecting bushmasters and able to support myself while I was doing it."" ""So I, I spent months and months in rain forests just looking, ah for bushmasters and catching them in a way that that would not hurt them" "The bushmaster is basically found over most of, ah" "South America and, and parts of Central America."" ""It requires a, a specific environment and, and that is ah, best met with, in a, a cool, ah dark, humid area like, like a rain forest."" "The bushmaster certainly is the ultimate snake in that it is so unique and so strange to most of the other snakes, and its rarity of course, makes it, ah the ultimate thing for herpetologists to go out and find" ""It is the largest of all vipers perhaps the heaviest of all poisonous snakes reaching a weight of, in excess of forty pounds" "It is the only New World, ah pit viper that, that lays eggs" "It has a spine in its tail which is completely unique to that genus which it vibrates in the sticks or leaves to produce a a warning sound like a rattlesnake."" ""I think I must have been about twenty-seven when I caught my first bushmaster" "I was alone in Surinam in in a rain forest area, and, ah, in, at night" "I had no gear, equipment" "And I simply had to free-hand it and throw it into my suitcase" "One, one case I was chased a bushmaster left a safe burrow and and actually pursued me a distance of about ten meters through the forest" "This snake sometimes is a, is a very dangerous customer."" "Basically, the, the idea is to capture with with the least-amount of stress onto the snake so that it will survive, ah transport and it will survive ah, ah, long enough to, to breed for you."" ""Okay."" ""You, you, of course bear in mind that it is all still a matter of luck."" ""Good job." "Ha, ha." "Good job."" ""Success."" ""You may walk ah, for two days and find one or you may walk for three months and not see one."" "Back in the United States" "Dean Ripa has successfully bred the black-head bushmaster and now has over forty specimens in captivity" "Dean's experience with these snakes led him to believe that there may be more than one species" "by studying his own snakes he began to suspect that the South American and the Central American bushmasters were entirely different based on variations in body structure" "Harry Greene and Kelly Zamudio at Berkeley were testing a similar idea" "By studying bushmaster DNA they came up with some startling results." "What was once considered a single species they actually found to be three." "This gives us a key to understanding how present-day snakes evolved." ""What we have on the screen are, are the sequences of three snakes." "And on the bottom we have the two Central American forms, and on the top we have the South American form."" ""And I have put these three up just to contrast, because if we move through the DNA here, move through the sequences, we can see that there is..."" ""...a very high similarity between the two Central American forms, but large differences between the two Central American forms and the South American form." "Um, the two Central American..."" ""...forms are not identical, though."" ""If you scroll through the DNA here you can see that there are also some differences not quite as many as, differences from the South American forms" "But there are also some differences between the two Central American forms" "Okay." "So from these..."" ""...raw data, the sequences and the differences between the different subspecies we can reconstruct an evolutionary tree that clearly indicates the relationship between the subspecies and the evolutionary history of the species as a whole."" "The South American bushmasters were separated from those in Central America by the uplifting of the Andes over twelve million years ago" "Then a mountain chain running down the middle of what is now Costa Rica separated the Central American bushmasters resulting in the evolution of three separate species of snake" "Geographic isolation forces all animals to evolve on their own separate paths" "Scientists can start to follow those paths back into snakes' evolutionary past by studying DNA the building blocks of life" ""The origin of snakes is a little bit muddied" "Ah, it certainly is something that happened over a hundred million years ago."" ""We feel pretty confident now that snakes arose from within a group of lizards."" "Whatever those lizards were, at some critical point, they are thought to have become burrowing creatures prompting a fundamental change in body plan" ""If you look among these groups of lizards the loss of limbs and elongation of the body is something that happened evolutionarily over and over again, probably dozens of times."" ""And it is as if certain groups of lizards have experimented with losing their legs and becoming elongate, crawling creatures."" ""Most of those experiments do not seem to go very far." "We only have a few species remaining today" "One of them really took off, and that is snakes."" "The remains of that successful experiment can be seen near the tail of this python skeleton" "Tiny spurs that were once hind legs actually protrude through the skin of living pythons" "But to get around snakes have come to rely on a complex system of muscle fibers and tendons wrapped around as many as three hundred ribs" "Flexing particular muscles allows snakes to move in several ways" "Large, bulky snakes move similarly to caterpillars as a wave of muscle activity travels from head to tail" "Called rectilinear locomotion it involves gripping the ground with the edges of their belly scales and dragging themselves forward" "While hunting for prey in a barn the corn snake finds itself between the tire and metal rim of an old wheel" "Unable to move from side to side the snake is forced to move more like an accordion" "But this concertina movement requires a lot of energy" "Once free of the wheel, it resumes its usual motion" "Snakes have adapted their limited methods of locomotion to work in a wide variety of habitats" "Through their unique evolution snakes have proven that you do not need limbs to run to climb, to jump, or to swim" "Living in the oceans presented the sea snake with a host of tricky adaptive challenges" "A paddle-like tail and a keel that runs along its belly allow the sea snake to glide effortlessly through the water" "A single lung that extends almost the full length of its body gives it buoyancy and allows it to dive up to three hundred feet and on one breath remain under water for up to five hours" "To guarantee a rapid kill when hunting fish and eels the sea snakes packs a powerful venom that makes it more toxic than its closest family member, the cobra" "Having adapted so well to the ocean dry land is not an option for many sea snakes" "Most sea snakes no longer have fully-formed ventral scales that grip the ground and allow snakes to move and survive on land" "The ventral scales are wide, flat-belly scales" "They are linked to the ribs by a series of muscles" "Acting in concert with other belly scales they perform like the treads on a tire making their dragging movement possible" "So effective are these scales that some snakes like the corn snake, can climb vertically" "Snake scales are actually part of the skin and not just a covering" "They protect the snake while allowing for considerable elasticity and flexibility" "But their uses may be as varied as their remarkable patterns and colors" "Snakes constantly change their skin" "Live cells beneath the surface separate and add to the cells above" "As the old cells break down the snake's outer skin thickens and is ready to be discarded" "A transparent scale known as the brill and covering the eye takes on a milky hue the clearest sign of the transformation to come" "With the help of a log or rock to rub against the snake literally crawls out of its skin in a process known as sloughing" "Only a ghost-like trace of the snake's pattern and coloration is left in the sloughed skin" "The pigment cells that give snakes their often-brilliant colors remain with the snake itself" "Snake skin can do many things including act as a brilliant disguise" "But it can do little about one particular enemy, the cold" "Snakes must rely on their external surroundings to warm up or cool down unlike mammals and other creatures that can regular their body temperatures" "That is why snakes cannot survive north or south of sixty-nine degrees latitude" "The red-sided garter snakes of North America deal with winter temperatures of minus forty degrees by hiding underground in the thousands" "In the warmth of spring, they emerge en masse" ""To a geologist, this is a simple limestone sinkhole" "But to a biologist, this is a gold mine."" "Doctor Robert Mason has been studying these snakes for over fifteen years and has solved many of the puzzles of their curious life cycle" ""Well, here we are in a limestone pit approximately the size of an average living room and I am surrounded by twelve fifteen thousand red-sided garter snakes."" ""These snakes afford an outstanding opportunity to study some very difficult questions because these numbers here are just unprecedented" "You will never see numbers of snakes like this anywhere else in the world."" ""There are several things that are involved with the over-wintering of these garter snakes" "Most animals when they come out in the spring they have the luxury of time" "These garter snakes do not have that luxury of time and so they kind of cheat the system in a little way and in by that I mean the male garter snakes produce their sperm in the fall and they store it over the winter" "And then when they come out of hibernation in the spring they are ready to go immediately" "And they immediately can court and fertilize a female."" ""Females, they are cheating the system as well" "These snakes, ah not only can they store sperm for six weeks these females are noted for storing sperm for literally years" "So years from now this female could produce viable offspring from a mating several years earlier."" "As the female emerges from the den she is approached by dozens of potential suitors" "Attracted by her unique scent, the males rub their chin against the female in the hope of stimulating her" "They create what is known as a mating ball around a single female a mass competition in which there can be few winners" "This one female may be their only chance to mate this year" ""How does the female, for instance choose that lucky male among the hundreds of suitors" "Currently we just do not have a good feeling for that" "In many other species of mammals, for instance the big males are the ones that mate with the females" "In the case of the garter snakes, that is just not so."" ""Sometimes we find large females mating with small males and vice versa" "So there are some other cues that are important to garter snakes..."" ""...that enable females to choose the proper mate" "The females, after they leave this den will disperse out into the fields and marshes where they will feed over the summer" "And that is where they are going to give birth at the end of August."" ""The babies are born live." "And there is a mystery with these babies" "There is a lost year, we call it" "Because in the fall, immediately after giving birth the females and the males..."" ""...the adult males, will return to these same dens" "But the babies are a myster" "We do not know where the babies are" "There are no first-year..."" ""...snakes in this den." "So, where are they?" "Where do they over-winter that first year?" "That is a great mystery to us and we want to try to figure that out."" "In most other species, like these Australian black snakes rival males will fight each other one-on-one for the right to mate" "But this combat can be a remarkably civilized affair more a ritualized dance than deadly battle" "In the pine barrens of North Carolina the corn snake emerges from its winter burrow" "It is spring, and he is ready to mate" "With snakes, mating is an act of sinuous grace and beauty" "Around a month after mating the female corn snake lays her eggs in a secure hollow" "Parental care ends here" "The corn snake embryos develop inside the protective, leathery shell" "After about two months the young corn snakes break through their shells" "Some emerge immediately" "Others may wait several days before heading out alone" "Throughout human history snakes have been the object of myths and legend, often as demons" "In the Garden of Eden, evil was embodied in the form of a snake condemned forever by God to crawl on its belly" "Yet there are many cultures where snakes are revered and endowed with magical powers" "In the northern Transvaal of South Africa a human fertility rite is about to be performed" "As the young women of the Venda tribe dance around the fire they link arms to symbolize the movement of a python" "The python is at the heart of many Venda legends" "One story tells of a python marrying two women" "Another says that a small python lives inside the women's wombs and plays a vital role in conception" "To the Venda, the snake is a potent life force, not an evil spirit" "The ancient Mexicans believe the snake to be a god linking not just the underworld with the heavens but the earth with the universe" "In the language of these lost civilizations the constellation of Scorpio was called Amaru, meaning snake" "The constellation had a spiritual influence over all of Central and South American cultures" "It has always been tempting for humans to mythologize snakes" "It is not hard to see why" "The ancestors of snakes emerged from an evolutionary experiment which left them without limbs" "Yet they are one of the great success stories of the natural world" ""Snakes have been around on the earth for millions of years..."" ""...and as far as I can tell they should be around for millions of more years" "As long as they are not interfered with..."" ""...there is no reason to believe they would not" "They are exquisitely well-adapted to the environment they live in." ""Given the opportunities they should be going on for millions more years."" "The end"