- CLASS: Reptilia (Reptiles)
- ORDER: Squamata
- FAMILIES: 17
- GENERA: About 420
- SPECIES: 2,978 known
SSSSensational serpents! Snakes, by and large, get a bum rap. Many people have a deep fear of these reptiles. Their long, slender bodies and lack of legs, eyelids, or ear flaps distinguish snakes from all other reptiles. They are covered with back-folded and pliable skin sections called scales. The skin between the scales is called interstitial skin. Like their reptile brethren, they use the heat of the surrounding air to regulate their body temperature. A flexible body allows snakes to stretch out to warm up quickly, to curl up to conserve body heat, or just to warm a particular part of the body.
It’s surprising how easily a snake can get from one spot to the next. By squeezing and relaxing the muscles down each side of its body, a snake is able to move forward. Most people think of "slither" when asked how a snake moves, but for a group of animals with the same basic body structure, different snake species can move in a surprising variety of ways. Even the way they slither can vary widely.
Special flattened scales on the underside of their bodies, called ventral scutes, give snakes traction. Snakes with scutes on just the underside of their body tend to move slower; faster snakes have scutes that extend upward to the sides of the body: the more scutes, the faster the snake. However, sea snakes have flattened tails that they use like paddles to propel them through the water, and some tree snakes are called flying snakes, although they don't really fly but flatten their body and spread their ribs to glide from tree to tree.
Snakes don’t have eyelids, so they can’t blink or close their eyes to sleep. Sometimes Zoo visitors think a snake is staring at them through the viewing glass, but maybe the snake is really just sleeping—it’s hard to tell. Snakes can’t see very well anyway and seem to notice objects only if they move. Most of the time they sense their prey through vibrations caused by movement. Snakes are sensitive to vibrations, particularly those made by land animals, but their most acute sense is smell.
HABITAT AND DIET
Snakes are found living on land and in water, as well as in every habitat imaginable—on every continent except Antarctica.
The can be found in open oceans, vast deserts, and mountain regions at altitudes of over 10,000 feet (3,000 meters). Those that live in places where it gets very cold in winter may hibernate in deep, underground dens, remaining dormant until spring brings warm weather again. Snakes that live in desert habitats often spend the heat of the day in burrows dug by other animals.
All snakes are strictly carnivores and have quite a varied diet: they eat mammals, such as mice, rats, and rabbits, fish, frogs, or even other snakes! There are some snakes that only eat eggs, usually those laid by birds. To get through that hard shell, an egg-eating snake has sharp bones in its throat that cut the egg open as it is swallowed. They then spit the shell pieces back out.
Snakes find their prey in a variety of ways: by sight, by using heat-sensing pits on the sides of their head (these snakes are called pit vipers) or on the lips, by sensing vibrations with their body, or "tasting" the air with their tongue to see what's nearby. Snakes have two main methods of finding food: active hunting for food or sitting in ambush, waiting for food to come to them. It's usually the larger snakes, like pythons, boas, and vipers that use the "sit-and-wait" technique, but even these snakes may have to move to another area from time to time if they are not successful.
Snakes can strike (or reach forward quickly to grab their prey) with amazing speed. Some just snatch small prey and begin swallowing immediately, others grip and constrict around their prey, squeezing tighter each time the victim exhales. These constrictors feel the heart beat of the prey and constrict until it stops. Venomous snakes inject a toxic complex protein into their prey that kills or paralyzes it.
Snake venom even helps the animal digest its meal. Spitting cobras have modified fans that squirt venom up to 6 feet. This is strictly a defense mechanism and benefits both snake and its predator by eliminating any physical contact. The venom severely incapacitates would-be attacker but does not kill it as a bit would. People often fear snakes for their venom, but only a third of snake species are venomous, and human deaths from snakebites are very rare.
Snakes don’t use their teeth to chew their food—they just swallow it whole. Can you imagine trying to stuff a whole watermelon in your mouth? Well, snakes can eat prey that is up to 20 percent of their body size! They begin their meal by swallowing prey headfirst, holding on with sharp teeth that point backward. Their mouth bones are loosely attached to each other and to the skull, and the lower jaws have a stretchy band of skin holding them together. Next, throat and body muscles help pull the prey into the esophagus. Also, the opening to the windpipe is at the front of the upper mouth and moveable, so snakes are able to breathe while swallowing.
Depending on the size of the meal, snakes may not have to eat again for several days, weeks, or months. There have even been cases where a large python didn’t eat for over two years!
Make way for baby snakes: Oviparous snakes lay from 2 to 16 eggs in a clutch, although some species lay up to 50 or more eggs. The mother snake incubates her eggs by burying them or by wrapping her body around them and "shivering" to generate heat. In some python species and the king cobra, the mother stays to protect her eggs from anything that would eat them; in other species, the eggs are left to hatch without any care from the parent. In some snake species the parent may stay around for a short period after the hatching.
Some female snakes bear live young rather than laying eggs, but whether they are viviparous or ovoviviparous is not known for most species. Live-bearing snakes benefit more in more extreme climates and at higher altitudes where the weather is colder, because the developing young can be kept warm inside the mother's body.
No matter how a snake comes into the world, once it arrives it is on its own, as the mother does not stay to raise her offspring.
A snake continues to grow its entire life, but its outer skin does not, so the snake needs to shed, or molt, its external skin from time to time. About two weeks before it is ready to shed, the snake stops eating and its skin turns dull as a fluid begins to separate the old skin from the new. To cast off the old skin, the snake may rub its head against a rough surface to help turn the skin inside out, much like you might pull off your socks!
A baby snake sheds soon after hatching or birth to help evade predators by leaving its scent and skin behind as it wiggles away. It grows quickly at first and sheds several times in the first year. As the snake gets older, it molts less often, perhaps just two to four times per year.
The warm months of summer are sometimes called snake season—not because there are more snakes, but because more people go outdoors in the summertime, often into snake territory. But remember: snakes don’t want anything to do with people. They would much rather hide and will only bite if they can’t get away from you or if startled. To be safe when hiking or camping, stay on trails and don’t reach into or stick your feet into rock piles, bushes, or logs where a snake might be hiding or sleeping. If you see a snake, don’t try to pick it up or get close to it. Just let it be. Chances are good that it will quickly crawl away, and you can both go about your business!
AT THE ZOO
Snakes have been a part of the San Diego Zoo’s animal collection since its inception. By 1922, a fine reptile house, which doubled as the Zoo’s entrance, exhibited 46 snake species, including pythons, 11 rattlesnake species, vipers, and boa constrictors. An aisle ran from the front to the rear of the building. On each side of the aisle, a large, oblong, concrete pool was built, with one providing a home for the water snakes.
Our first snakes were gathered from the Zoo grounds itself. As construction of the fledgling zoo continued, workmen found so many snakes that the Zoo was able to trade them with other zoos! Our most famous snake resident in those early years was Diablo, a 200-pound (90 kilogram) python brought from India in 1924. This impressive animal refused any food item offered him, so large sausages were forced down his throat with a meat grinder while six men held him. Word of this feeding strategy drew so many onlookers that soon the Zoo posted feeding times for Diablo and used them as fund-raising events! Our Zoo’s founder, Harry Wegeforth, M.D., wrote “All during this snake’s life, it never once ate of its own volition, yet it lived longer and more healthily than snakes who ate normally.”
In 1936, a new Reptile House opened, and it continues to delight and awe visitors today. A stroll around its perimeter allows you to safely view an amazing collection of pythons, cobras, boas, rattlesnakes, king cobras, and rinkhals, which are true spitting cobras that also “play dead.” Because you’re on the outside looking in, you’re not bothered by the heat and humidity required to maintain some of our snakes. Each enclosure is designed to look like the resident’s natural home. Youngsters proudly point out to their parents which snakes are venomous–with the help of the appropriate signs! Some corners of the House feature the giants of the snake world: anacondas and pythons.
There are other areas of the Zoo where snakes can be seen, too. Our Elephant Odyssey is home to a variety of rattlesnakes that are native to the San Diego County region, including the largest rattler in our area, the red diamond rattlesnake. Lost Forest features snakes native to rain forest areas. A few of our snakes make appearances in animal presentations, giving guests an opportunity to touch these unique creatures.
Our Reptile Walk in Discovery Outpost, across from the Galápagos tortoise habitat, opened in July 2012. One building features native reptiles and includes Baja California rat snakes, California kingsnakes, red-sided and San Francisco garter snakes, and rosy boas.
S.O.S. (save our snakes): With snakes so widely distributed around the world, habitat loss and hunting for food or trade in snakeskins can have an impact on their survival. Yet when you consider how quickly rodents and rabbits reproduce, we owe a big thanks to snakes for helping control these populations. Scientists have been researching ways snake venom can be used in human medicine.
It is estimated that 30 percent of South American snakes and lizards are endemic to the Brazilian Atlantic Forest. One of these species is the golden lancehead snake, which inhabits Brazil’s Queimada Grande Island, nicknamed Snake Island. The golden lancehead is at critical risk due to collection of snakes for the illegal animal trade and natural disasters such as wildfire.
In 2011, a studbook was created by a San Diego Zoo Global collaborator in Brazil to help manage the captive population of these snakes, and we hope to start another colony at the Animal Reproduction Laboratory at the University Cruzeiro do Sul in Sao Paulo, Brazil. In addition, six first-generation zoo-bred snakes may one day form the nucleus of a third assurance colony at the San Diego Zoo. We believe that increasing research and educational outreach among the island’s people will decrease illegal activities there. A better understanding of population dynamics and factors affecting this species will help us establish more direct actions for golden lancehead conservation.
Diverse in size and color, with an important role in the web of life, snakes should be appreciated for their beauty and respected as fellow dwellers on this planet. Please leave them be.