Snakes and Lizards: Squamata

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SNAKES AND LIZARDS: Squamata

PHYSICAL CHARACTERISTICS

The 7,200 species of snakes, lizards, and wormlizards all fall under the order Squamata and are therefore known as squamates (SKWAH-mates). Perhaps the most noticeable difference between the snakes and the lizards are the legs, or the lack of them. Most lizards, except for a few species, have working legs. Snakes are legless. The most noticeable feature of the worm lizards is their earthworm-like body. While they have scales and earthworms do not, worm lizards' scales are arranged in rings and separated with grooves to give them the appearance of an earthworm's ringed body. Most of the worm lizards are legless, although a few have two front legs just behind the head.

Besides smelling with their noses and tasting with their tongues, most squamates also smell with a special organ on the roof of their mouths. They use it by first flicking or otherwise picking up chemicals on the tongue. They then place the tongue on the roof of the mouth at what is called the Jacobson's organ, which smells the chemicals. For hearing, many lizards have ears that are visible as a hole on either side of the head. Neither the snakes nor the wormlizards have the openings for their ears. Scientists believe that snakes can probably only hear very low-pitched sounds, including ground vibrations that they sense in the jaw and send to the ear.

In addition to the presence or absence of ear holes, known as external ears, snakes and lizards have another obvious difference. The majority of lizards have eyelids that close and open. Snakes, on the other hand, have a spectacle over their eyes. A spectacle is a clear scale, which looks much like a contact lens. In other words, a lizard noticeably blinks, but a snake always appears to have its eyes open. Although most squamates have obvious eyes, those species that spend most of their lives underground often have very small eyes, which are sometimes invisible under their scales.

The size of the squamate depends on the species. Among the lizards, the heaviest is the Indonesian Komodo dragon, which can grow to be at least 9.9 feet (3 meters) long and 330 pounds (150 kilograms). Many people consider the crocodile monitor to be the world's longest lizard. It can reach 12 feet (nearly 3.7 meters) long, although some reports claim that the lizards can reach 15 to 19 feet (4.6 to 5.8 meters) long. The smallest lizard, on the other hand, is the jaragua lizard, also known as the dwarf gecko. From one end to the other, adults of this recently discovered species only reach about 1.2 inches (3.2 centimeters) long. Snakes also come in different sizes. Some of the smallest are in the blind snake and slender blind snake families, which include species that only grow to 4 inches (10 centimeters) long and weigh just 0.05 ounces (1.4 grams). This compares to the reticulated python, which often reaches 20 feet (6.1 meters) or more. The largest reticulated python ever discovered was killed in 1912 in Indonesia. This beast measured 33 feet (10.1 meters) in length. The South American green anaconda is another enormous species, often reaching 25 feet (7.7 meters) long and 300 pounds (136 kilograms). Wormlizard adults range from 3.1 inches (8 centimeters) to more than 32 inches (81 centimeters) long.

GEOGRAPHIC RANGE

Besides the Arctic, Antarctic, and other very cold places, squamates live almost the world over.

HABITAT

Squamates can live in many habitats, from the dry conditions in the desert to the wet and warm rainforests. Many of them, including numerous lizards and snakes, live above ground on land. Some, such as the wormlizards, are fossorial (foss-OR-ee-ul), which means that they remain underground most of the time. Others, including many snakes, are arboreal (ar-BOR-ee-ul), which means that they often live above the ground among tree branches. Some, like the water snakes, rarely leave their freshwater streams or ponds, while the sea kraits are snakes that spend their lives in salt water.

DIET

Most of the squamates eat other animals. Many of the lizards and the smaller snake species eat insects or other invertebrates (in-VER-teh-brehts), which are animals without backbones. Even some of the medium-sized snakes eat invertebrates. Eastern garter snakes, for example, like to dine on earthworms. A large number of the medium- to large-sized snakes, however, eat other snakes, lizards, frogs and tadpoles, mammals and other vertebrates (VER-teh-brehts), which are animals with backbones. Boa constrictors, pythons, and other very large snakes sometimes eat calves, deer, and other big mammals. Monitor lizards, which can grow to 12 feet (3.7 meters) or longer, can also capture, kill, and eat large mammals, such as deer, monkeys, wild pigs, and even buffalo. They are also known to eat dead animals, or carrion (CARE-ee-yun), that they come across. Some species of squamates eat plants either in addition to or instead of meat. Many of the iguanas, for instance, eat flowers, fruits, and leaves.

All squamates shed their skin—actually just the outer layer—once a year. If a snake eats well and grows quickly, it may shed additional times. The lizards typically shed in small pieces, while the snakes usually shed in one piece that peels off inside out. Often, a shed snake skin still shows enough of the animal's patterns for a careful observer to identify the species that left it.

SHOWING OFF OR BLENDING IN?

The beautiful stripes, bands, and blotches on many snakes and lizards may be helping the animal to blend into the background or to show off to predators or to mates. Most of the time, the patterns camouflage the snake or lizard by breaking up its outline and making it difficult for predators to see where the animal's body begins and ends. A striped snake, for example, may look quite noticeable on the pavement but almost disappear when placed on the many-colored forest floor where it lives. Some species, however, benefit from advertising themselves. The bright colors of numerous snakes warn potential predators to stay away, and the brilliant hues in some male lizards attract females during the mating season.

BEHAVIOR AND REPRODUCTION

Because they are ectothermic (ek-toe-THERM-ik), which means that their body temperature changes based on the outside temperature, many squamates sunbathe, or bask, to warm up. Others, however, stay out of sight during the day. Some of the fossorial species rarely come out of the ground at all. These species will sometimes increase their body temperatures by moving to a warmer underground spot. For hunting, many of the squamates actively walk or slither about looking for prey. Others, however, hunt by ambush, which means that they sit still, wait for a prey animal to come along, then spring out to grab and eat it. Some snakes, including the pit vipers and the boas, have a special method of hunting. They can sense heat through small holes, called pit organs, on the face. Using these pit organs, they are able actually to see the heat given off by an animal in 3-D. These pit organs come in especially handy when hunting for food at night or in places where the snake has a limited view.

Compared to mammals and birds, squamates must have meals much less frequently. Because they are ectothermic and do not have to use their energy to keep up a constant body temperature, as the mammals and birds do, they can get by on much less food. Some of the large snakes can survive many months —even a full year—on one big meal.

Depending on the species, a squamate female may lay eggs or give birth to live young. Many species lay their eggs in nests, which are little more than holes dug in moist ground. A few, like the wormlizards, lay their eggs inside ant or termite nests. Most squamate mothers provide no care for their young and leave almost immediately after they lay their eggs or give birth. Some lizards and snakes are exceptions. Many female skinks, for example, stay with the eggs until they hatch.

While most species reproduce only after the male and female mate, some species are parthenogenic (parth-enn-oh-GEN-ik), which means that a female can produce young by herself. In many of these species, such as the lizard known as the desert grassland whiptail, only females exist. The female's young are all identical copies of herself. Besides this species in the whiptail family of lizards, seven other families of lizards and snakes have some all-female species.

THE SHELL GAME

When it comes to living on dry land, the snakes, lizards, and worm lizards, known as squamates, have a big advantage over the frogs and salamanders. Most squamates lay eggs, just like the frogs and salamanders do, but the squamate eggs have shells. Even though the shells may be quite thin and often even flimsy, they help protect the eggs from drying out before they hatch. Without the shell, squamates would have to follow the pattern of the frogs and salamanders and lay their eggs in the water or some other wet spot. With the shell, however, the snakes, lizards, and worm lizards can make their homes well away from the water. This has allowed squamates to exist in nearly every habitat around the world.

SQUAMATES AND PEOPLE

For the most part, squamates either freeze or flee when humans approach. If a person comes too close, however, many will bite. Fortunately, most species are not venomous, and the bite only serves to surprise the person rather than hurt him or her. Some snakes, and two species of lizards, are venomous. The lizards are the Gila monster and the Mexican beaded lizard. Usually, quick medical attention can treat squamate bites.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists 265 species as being at risk or as already extinct, which means they are no longer in existence. Of these, 14 are Extinct, 36 are Critically Endangered, and 31 are Endangered. Critically Endangered means the species faces an extremely high risk of extinction in the wild. Endangered means the species faces a very high risk of extinction in the wild. Many of these species have been hurt by habitat loss or by the introduction of new species, especially predators, to their habitat.

FOR MORE INFORMATION

Books:

Badger. D. Lizards: A Natural History of Some Uncommon Creatures — Extraordinary Chameleons, Iguanas, Geckos, and More Stillwater, MN: Voyageur Press, 2002.

Cleaver, Andrew. Snakes and Reptiles: A Portrait of the Animal World. Wigston, Leicester: Magna Books, 1994.

Greene, Harry W. Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press, 1997.

Lamar, William. The World's Most Spectacular Reptiles and Amphibians. Tampa, FL: World Publications, 1997.

Mattison, Chris. Lizards of the World. New York: Facts on File, 1989.

Mattison, Chris. The Encyclopedia of Snakes. New York: DK Publishing, 1997.

McCarthy, Colin. Eyewitness: Reptile. New York: DK Publishing, 2000.

Montgomery, Sy. The Snake Scientist (Scientists in the Field). Boston: Houghton Mifflin, 2001.

O'Shea, Mark, and Tim Halliday. Smithsonian Handbooks: Reptiles and Amphibians (Smithsonian Handbooks). New York: DK Publishing, 2002.

Pianka, E. R. Ecology and Natural History of Desert Lizards: Analyses of the Ecological Niche and Community Structure. Princeton, NJ: Princeton University Press, 1986.

Pianka, E. R., and L. J. Vitt. Lizards: Windows to the Evolution of Diversity. Berkeley: University of California Press, 2003.

Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd edition. San Diego: Academic Press, 2001.