There are many different animals in the world. Animals may eat plants or meat to live. They live in different types of environments all around the world. Their bodies help them to survive in their habitat.
Predators and Prey
Predators are animals that hunt and eat other animals for food. Prey are the animals that predators hunt. A lion is a predator that hunts for prey such as the wildebeest or a zebra. The killer whale will eat sea animals such as sea lions or seals.
Warm-Blooded and Cold-Blooded
Some animals are cold-blooded. These animals depend on heat from outside their bodies to keep warm. Snakes and lizards are cold-blooded animals that bask in the sun on rocks to warm their bodies. The bodies of warm-blooded animals stay at about the same temperature all the time. Humans and other mammals are warm-blooded animals.
Invertebrates and Vertebrates
Most animals are invertebrates. These animals do not have a backbone, or spine. Some examples of invertebrates are insects, snails, octopi, worms, and jellyfish. Vertebrates have a spine inside their bodies. Mammals, birds, reptiles, amphibians, and fish are all vertebrates.
Some organisms are really small, or microscopic. They can be seen only with a powerful microscope. Living things that have only one cell are called single-celled organisms. Many single-celled organisms used to be placed in the animal kingdom. Today they are part of the Protista kingdom and are called protozoans. Some protozoa eat other organisms. Other protozoa make their own food using sunlight like plants. Amoebas are one type of protozoa. They live in water and other moist places. Many single-celled organisms live in large groups called colonies. Some types live inside tiny shells. When they die, their shells eventually become chalk. Bacteria are also single-celled microscopic organisms. They used to be considered animals but because bacteria don’t have a nucleus, scientists now put bacteria in the kingdoms Eubacteria and Archaebacteria. Bacteria are the most widespread form of life on the planet. They are found in the air, soil, and water, and in plants and animals. They live in colonies. Bacteria are either round, spiral, or rod-shaped. Bacteria have different roles in the environment. Some bacteria help digest food in plants and animals. Other bacteria break down dead plants and animals. Harmful bacteria in food and water can make you sick. Bacterial infections inside the body of an animal can be dangerous.
Mollusks, Sponges, Starfish, and Worms
Mollusks are invertebrates with soft bodies. Most mollusks live underwater. They include limpets, clams, oysters, mussels, squids, octopuses, and some snails. Some types of mollusks live on land. They include land snails and slugs. Some mollusks protect themselves by making hard shells around their bodies. Squids and octopuses are the most complex mollusks.
Sponges are the simplest form of multi-cellular animals, or animals that are made of more than one cell. Most sponges live in shallow water, but some live deep in the ocean. If a piece breaks off of a sponge it will grow into a new sponge. Sponges eat small pieces of food by pulling them through tiny holes in their bodies. The skeletons of some sponges can absorb water when they die. People sometimes use these skeletons for bath sponges.
Starfish, also known as sea stars, are star-shaped organisms that have five arms. The skin on their bodies has many spines. This helps protect them from predators. Starfish move using tube like feet that are found under each arm. Each tube foot has a sucker at the end. The suckers allow starfish to stick to rocks and to hold onto prey. They eat live coral, crabs, and mussels.
Worms come in many sizes and shapes. Some are flat, and some are round. Tapeworms and flukes have flat bodies. Tapeworms live inside the intestines of vertebrates. One type of fluke lives inside the liver of mammals. Animals that live inside other animals and cause harm to their hosts are called parasites. Roundworms have bodies shaped like a tube. Some are parasites, and some live in the ground or in water. Segmented worms include earthworms and leeches. These types of worms have long bodies with many sections, or segments. They live in the ground and eat dead leaves. They have no eyes and five blood vessels with valves that work like hearts. Leeches live in water and on land. They have suckers at both ends of their bodies. Some leeches suck blood for food.
Arachnids, Crustaceans, and Insects
Arachnids, crustaceans, and insects are the largest group of invertebrates. All these animals have bodies with several segments. They have hard shells called exoskeletons. They leave their shells, or molt, as they grow bigger. Then they make new shells.
Arachnids include spiders, scorpions, mites, and ticks. They all have eight legs. Spiders live anywhere that there are insects to eat. Some spiders spin webs to catch their prey. The trapdoor spider makes a tunnel in the ground and lines it with silk. The spider waits for an insect and opens its door to catch the prey. They use long teeth, called fangs to kill or stun their prey. Scorpions have claws to hold their food. Sometimes, they use stingers at the end of their abdomens for defense. Mites are tiny parasites that live on animals, plants, and food. Ticks suck the blood of warm-blooded vertebrates. Both mites and ticks can spread disease.
Most crustaceans live underwater. Their bodies have many segments that bend when they swim or crawl. Attached to each segment are pairs of legs, claws, or antennas. They have two sets of antennas on their heads. Crustaceans include barnacles, crabs, lobsters, and shrimp. Barnacles cling to rocks, shells, and other animals in the sea. Crabs and lobsters have big claws for holding and eating food. Shrimp breathe and eat with their feet. The only crustaceans that live on land are some crabs and pill bugs, or wood lice.
Insects live almost everywhere. Some insects crawl along the ground. Many fly in the air. All insect bodies have three parts. The head has eyes and antennae. The middle part, or thorax, has legs for walking. Most insects have six legs. Some have wings. The back end is called the abdomen. There are many different types of insects. Ants crawl around in search of food and bring it back to their colony. Dragonflies and beetles fly through the air. Dragonfly wings stick out away from their bodies. Beetle wings fold up across their bodies. The eyes of flies are very complex. They are called compound eyes because they have thousands of parts. Bees and wasps have stingers to defend themselves. They can sting people or animals if they are attacked or threatened. Mosquitoes are small. They suck the blood of mammals through a long mouth part called a proboscis.
Fish are cold-blooded vertebrates that live in water. Most fish are covered in scales and have fins to help them move. Gills let them breathe underwater. Many fish live in the ocean. The ocean water has salt in it. Other fish live in freshwater, or water that is not salty. Lakes, marshes, ponds, rivers, and streams all contain freshwater. Some people keep fish as pets. The fish live in glass containers called aquariums.
Most fish lay many soft eggs in the water. This is called spawning. The eggs are fertilized by the male fish in the water and are left to hatch on their own. Grunion are silver-colored fish that live in California waters. They wriggle onto the beach under a full moon to spawn. Salmon live in the ocean but return to freshwater to spawn. They swim up streams against the current. Fish have many ways to protect themselves from predators. A puffer, or blowfish, inflates like a balloon. Enemies are frightened away or are not able to bite the fish. Puffers are also poisonous, and some have spines.
The lungfish has both gills and lungs. The lungfish can live in water with little oxygen. It can even breathe air when the water dries up.
Many people think sharks are dangerous. They are good predators, but most are harmless to humans. Sharks skeletons are made of a softer material called cartilage, instead of bone. Sharks have many rows of teeth. Some types of sharks give birth to live offspring. This means that the babies grow inside the mother’s body until they are born. The hammerhead shark and tiger shark both give birth to babies this way.
Some sharks, like the grey nurse shark, have eggs that hatch inside the mother. The babies that hatch first sometimes eat the other eggs. Other sharks lay eggs that hatch outside the mother’s body. A horn shark egg is covered in a leather-like case to protect the egg while it is waiting to hatch.
Amphibians are cold-blooded vertebrates. They have a lot in common with both fish and reptiles. Amphibians include frogs, toads, salamanders, newts and caecilians. Frogs have smooth, wet skin. Toads have dry, warty skin and spend more time on land. Salamanders and newts are like lizards, but they do not have scales.
Most amphibians lay eggs in the water, like fish. The eggs hatch into larvae that have gills and live underwater. The larvae of frogs and toads have tails but no legs. They are called tadpoles. Tadpoles develop back legs and then front legs before their tails disappear. The larvae of salamanders and newts look more like adults. As an amphibian larva grows, its gills disappear and lungs develop. Amphibians eat insects and other small invertebrates such as turtles and snakes. Frogs and toads have long tongues to catch their prey. They have long back legs for jumping. Most frogs and toads make loud sounds with their throats.
Reptiles are vertebrates that have dry skin covered with scales or bony plates. They do not have feathers or fur. Most reptiles lay eggs with tough shells. Many reptiles have short legs while some have no legs at all. They are cold-blooded and breathe air. Reptiles include alligators, crocodiles, lizards, snakes, terrapins, tortoises, and turtles.
Alligators and Crocodiles
Alligators and crocodiles look very similar. They both have long bodies and tails. Some are very large. Their skin is thick and scaly. Crocodiles have thin noses, and alligators have broader noses. They have many sharp teeth. Alligators and crocodiles live near water and swim well. They eat fish and often attack animals that come to drink. They lay eggs on land.
Lizards are the largest group of reptiles. They have a small head, short neck, and a long body and tail. Lizards can be small like a gecko or quite large like the Komodo dragon.
Most lizards have four legs but some lizards have no legs. They look like snakes except they have eyelids and ears. Other types of lizards can run fast. One type of lizard, the basilisks, can run across the surface of water. Some lizards swim well, and others are good climbers. Most lizards eat insects but some eat birds or other reptiles and some eat mostly plants. Nearly all lizards lay eggs, but a few types give birth to live offspring. Many lizards can lose their tails to escape when they are attacked. A new tail will grow back in its place. Two types of lizards, the Gila Monster and Beaded lizard are poisonous.
Find out more... Some Lizards Can Change Colors
The chameleon is a lizard that can become the color of whatever it is sitting on! Well, at least the colors of trees and rocks. The chameleon also has strange eyes. They can spin, or rotate, in different directions at the same time.
Snakes have long, narrow bodies covered in a scaly skin. A snake’s skin can be one solid color or it can be multi-colored with different markings or patterns. Snakes do not have eyelids, external ear openings, arms, or legs.
Some snakes slither quickly along the ground. Others climb trees. And still others swim in the water. Different kinds of snakes live in different habitats. Different types of rattlesnakes are found all over North America. Rainforests are home to boa constrictors. Sea snakes, like the turtle-headed sea snake live in the water.
Snakes eat other animals. They do not chew their food. They have flexible jaws that open wide to swallow their prey whole. Many snakes eat their prey while it is still alive. Others kill their prey first. Snakes’ jaws can open wide to swallow prey.
Boa constrictors and pythons squeeze their prey to death. A poisonous snake injects its prey with venom. Cobras, mambas, and copperheads are all snakes with poisonous venom. A rattlesnake has a special part on its tail that it shakes to warn enemies. Some snakes have special holes, or pits, that sense differences in heat. These snakes can find their prey in the dark.
Terrapin, Tortoises, and Turtles
Most terrapins, tortoises, and turtles are very similar. They have large, bony shells covered with big scales. They can pull their heads, arms, and legs inside the shell when they are threatened. So, why do we have three different names for this group of reptiles? The names are based on the three types of habitats these reptiles live in. Terrapins spend time both on land and in the water. They always live near freshwater areas like marshes, ponds, and streams. Many have adapted to life in brackish, swampy areas. Some terrapins hibernate during the winter months. The box turtle is actually a terrapin.
Tortoises are turtles that live on land. They have high shells that protect them. Their strong, stumpy legs help them walk on land and dig burrows. Many tortoises have adapted to life in hot, dry areas.
They go into underground burrows when the sun gets too hot. Giant tortoises live a long time. Tortoises can live to be over 100 years old.
Turtles spend most of their lives in the water and lay their eggs on the land. Turtles usually have webbed feet for swimming. Sea turtles live in saltwater. Their webbed feet are like paddles. The biggest reptile is a kind of sea turtle called a leatherback. Other turtles live in freshwater like marshes, ponds, streams, and lakes. They swim but also can be seen basking in the sun on logs, rocks, or the banks of the water.
Find out more... Dinosaurs
Dinosaurs were a group of reptiles that lived in the Mesozoic era millions of years ago. The Mesozoic era is divided into the Triassic, Jurassic, and Cretaceous periods. All the dinosaurs died at the end of the Cretaceous period. They became extinct. Because there were no people during that time, we only know about them from fossils and from related animals that are still alive today. The word “dinosaur” is often used for any large reptile that is now extinct. Dinosaurs lived mostly on land. Many were very large, like the Brachiosaurus. The smallest dinosaur was the size of a chicken. Some dinosaurs ate plants. Triceratops was a group of planteating dinosaurs with three horns and large, bony plates on their necks. They walked on all four legs. Some dinosaurs hunted other animals. Tyrannosaurus rex is the species name of a large dinosaur that ate other animals. It had a big head and sharp teeth. It walked on its back legs and had small front legs. Other reptiles related to dinosaurs lived at the same time as dinosaurs. Plesiosaurs were marine reptiles with flat bodies, long necks, and flipper like feet. The pterodactyl was a reptile that could fly. It had wings and a beak, like birds. But it did not have feathers.
Birds are warm-blooded vertebrates. They are the only animals with feathers. Their two front legs are wings. Most birds use their wings to fly. Birds use their hind legs and feet for walking, swimming, or holding onto branches. Most birds have tails. All birds lay eggs with hard shells. Most birds build nests to keep their eggs safe and warm. They may use leaves, twigs, grass, feathers, or paper.
Birds have sharp beaks for eating. They may eat insects, seeds, nectar, or other animals. A woodpecker has a very hard beak for making holes in tree trunks. Some woodpeckers eat insects found in the holes. Others drink the sap that oozes from the holes.
A pelican is a large bird that eats fish. It can carry a whole fish in the large sac in its throat. A hummingbird is a tiny bird with a thin beak. It uses its long tongue to drink nectar from flowers. Hawks and other birds of prey have a hooked beak for ripping and tearing apart prey.
Birds of prey hunt animals, including other birds. They have long, sharp claws called talons. These birds include owls, hawks, and eagles. Owls can turn their heads to look behind them for prey.
Some birds have beautiful feathers. They use them to attract mates. A male peacock has long, colorful feathers in its tail. It spreads its tail like a fan. A parrot has many bright colors. It can repeat, or mimic, sounds that it hears. You can teach a parrot to repeat words. Penguins are birds that cannot fly. They use their wings to swim. Penguins wings work like paddles under the water. The Galápagos penguin lives near the equator, the hottest part of the world. The emperor penguin lives in Antarctica, the coldest part of the world.
Ducks, geese, and swans float on water. They have broad, flat feet with pieces of tissue, or webs, between their toes. These webbed feet are like paddles that help the birds swim on top of the water.
Ostrich are one of a few types of birds that cannot swim or fly. The ostrich is a large bird that lives in Africa. The body of the ostrich is too large for its wings to lift it off the ground. It has big, powerful legs and can run very fast. The rhea in South America and the emu in Australia are like the ostrich.
Getting to know... John James Audubon
John James Audubon was born in 1785 and grew up in France. His family sent him to live in the United States when he was eighteen. He lived on a farm in Pennsylvania. Audubon loved nature and art. He decided to draw every type of bird in North America. He drew male and female birds. He drew illustrations showing birds caring for their young and their feeding habits. Audubon could not find people who were interested in his paintings. So, he took his pictures to England and Scotland. He earned enough money to begin publishing The Birds of America. The book had very large pages. It showed a thousand different birds from five hundred species. Audubon also wrote about the behavior of birds. The Audubon Society was named to honor John James Audubon and works to protect birds, other wildlife, and their habitats.
Mammals are probably the animals you know best. Humans are mammals. So are dogs and cats. Mammals share some similar traits. They are all warmblooded vertebrates. They have at least some hair or fur on their bodies. Female mammals have special body parts called mammary glands. These glands make milk that baby mammals drink. Almost every mammal gives birth to live offspring. A few types of mammals such as kangaroos have a pouch where the baby continues to grow after it is born. A couple of mammals even lay eggs.
Bears are one type of large mammal. All bears have long fur and strong claws. Bears may eat fruit, insects, fish, and other animals. Sometimes, they stand on their back legs to eat or to scare their enemies. Some bears hibernate. That means that they sleep through the winter when food is hard to find. Polar bears are the biggest bear. They live in arctic areas and have white fur. Polar bears have two types of fur. Thick, woolly fur keeps them warm while guard hairs keep them dry. Polar bears catch fish and hunt seals.
Some wild mammals are related to domesticated cats. Cats are one type of mammal that comes in many sizes and colors. Cats hunt other animals and have sharp teeth and claws. Many are good climbers. Tigers are the largest cats. They live in Asia. Most tigers are orange with black stripes. Unlike other cats, tigers like water. They hunt alone rather than in a group.
Lions have light brown fur. They live in Africa. It is easy to tell if the lion is male because he has long, darker fur around his head called a mane. Lions live in a group called a pride. Usually, only one male lion will be in the pride. The female lions hunt for food for the pride and will hunt in a group. Leopards live in Asia and Africa. They have light brown fur with black spots. A leopard hunts alone and drags its prey into a tree to hide it from other hungry animals.
Some wild mammals are related to domesticated dogs. These mammals are predators that often hunt in groups, called packs. Coyotes look like a small, light brown wolf. They live in North America and may hunt near people’s homes. A coyotes howling and other sounds are one of the few wild mammal sounds commonly heard by humans. Foxes are smaller than coyotes and have a bushy tail and large ears. Foxes are well adapted to all habitats such as the arctic, deserts, forests, and grasslands. Jackals look like the coyote. They live in Africa and Asia. Jackals usually live alone or in pairs. Wolves are larger than most domestic dogs. They may be gray or red. Wolves live in North America, Europe, and Asia.
Elephants and Rhinos
Elephants are the biggest land animals. Adult elephants can weigh six tons (5443 kg) or more. There are different types of elephants in different parts of the world. The African elephant is larger than the Asian or Indian elephant and also has bigger ears. Male elephants have long teeth called tusks made of ivory. Muscles in an elephant’s trunk let it pick up objects and drink water. Elephants eat hundreds of pounds of plants every day.
Find out more...
Elephants have few natural enemies except man. They are in danger of extinction because of loss of habitat and poaching. Elephants are hunted for their ivory tusks which have been used to make items such as jewelry and piano keys. They are listed as an endangered species. Conservationists are trying to protect the elephant by making laws to ban the sale of ivory.
Rhinoceros, or rhinos, are another large mammal from Africa and Asia. They have thick gray skin and little hair, like the elephant. A rhino has one or two horns on its nose.
Many mammals have a hard piece on the bottom of each foot called a hoof. They eat plants and often live in groups called herds. Many have horns or antlers on their heads. Some of these mammals are domesticated, such as horses, cows, sheep, goats, and pigs. Other hoofed mammals live in the wild, such as antelope, bison, deer, giraffe, and zebras. Zebras live in Africa. Zebras are like horses with black-and-white stripes. Giraffes also live in Africa. They have long legs and a very long neck. Giraffes can reach leaves at the tops of trees. Camels live in the deserts of Africa and Asia. They are a large animal that has one or two humps on its back. Camels have one nail and a large, soft pad instead of a hoof. This helps them walk on sand.
Marsupials are mammals with a pouch. The pouch is where the developing young marsupial lives when it leaves its mother’s uterus. In the pouch a baby marsupial finds a nipple where it can drink the milk from its mother. The baby will complete its development in the pouch. It will not leave the pouch until it can survive outside. Most marsupials live in Australia and South America. Kangaroos are the largest marsupials. They have small front legs, large back legs, and a thick tail. The kangaroo uses its back legs to leap high and far. It often stands on its back legs. Kangaroos eat plants. A baby kangaroo is called a joey. The joey may ride in its mother’s pouch to feed or travel until it is a year old.
Koalas are another marsupial from Australia. They look like a bear. Koalas live in eucalyptus trees and eat the trees leaves and young bark. A female koala carries its baby on its back until the offspring is a year old. Opossums are the only marsupial native to North America. They have a long nose and a tail like a rat. Opossums can hang upside down by their tails. They often live near people and search garbage cans for food. Opossums will eat both plants and animals.
Humans belong to the group of mammals called primates. The other primates are apes, monkeys, and lemurs. Primates depend on their eyesight to find food or locate a mate. Their eyes are on the front of their faces. Primates see the world with both eyes at the same time. The image seen by one eye overlaps with the image that the other eye sees. This gives primates a good sense of depth, or how far away something is. Primates can see in color, unlike most other animals. Primates have bodies that are good for climbing trees. They have long arms and legs. Their thumbs are opposable. This means that the bone of the thumb can turn, or rotate, to touch the other fingers. The hands of primates can hold branches or food.
Primates have nails instead of claws. They have small folds on the palms of their hands and soles of their feet to help them hold objects. In humans, these folds are fingerprints. Lemurs and many monkeys have long tails. Apes and humans do not have tails.
Apes live in Africa and Asia and on some islands in the Pacific Ocean. They have no tails. Apes include gorillas, chimpanzees, orangutans, gibbons, and siamang. Gibbons are small apes. They have very long arms and swing from tree branches. Chimpanzees live in Africa. They are smaller than gorillas and have dark fur and skin. Chimpanzees walk on their knuckles like the gorillas, but spend more time in trees.
Chimpanzees may use tools in the wild. They will use a stick to get ants or termites out of a hole or to scare away an unwanted intruder. Gorillas live in Africa. They are very large and strong. Gorillas have dark fur and skin. They walk on their feet and the knuckles of their hands. They can climb trees, but do not do so very often. Gorillas eat mostly plants, but they may also eat meat.
Orangutans live on the Pacific islands of Borneo and Sumatra, near Asia. They have brown skin and long red fur. Orangutans climb with their hands and feet. They live in trees and eat plants.
Lemurs are small primates. They live on the island of Madagascar, near Africa. They have small heads, large eyes, soft fur, and a long bushy tail. Most lemurs eat leaves, fruit, flowers and sometimes insects or small vertebrates. Some scientists put lemurs in their own group because they have some differences from other primates.
Monkeys are called either New World monkeys or Old World monkeys. New World monkeys live in Central and South America. They live in trees and have long tails. Some use their tails to hang from trees. Howler monkeys can make loud noises. Old World monkeys live in Africa and Asia. They have small tails. The baboon has a long nose, lives on the ground, and eats both plants and animals.
Getting to know...
Three women are famous for studying the behavior of apes. Jane Goodall was born in England in 1934. She went to Tanzania, in Africa, to study chimpanzees. Dian Fossey was born in San Francisco in 1932. She went to Zaire, in Africa, to study gorillas. Biruté Galdikas was born in 1946 and grew up in Canada. She went to the Pacific island of Borneo to study orangutans. All three women were students of Louis Leakey. He was both an anthropologist, a scientist who studies humans, and a paleontologist, a scientist who studies fossils. He wanted to learn about apes so he could understand humans better. Goodall, Fossey, and Galdikas lived with the apes and got to know them well. They studied the social system of the animals. They tried to protect the apes from human diseases, the destruction of their habitats, and poachers.
A rodent is a small mammal. All rodents’ front teeth continue to grow like your fingernails. They gnaw on food or other things to grind down their front teeth. Rodents often nibble nuts and seeds in small bites. Rodents that live in the wild include squirrels, gophers, porcupines, chipmunks, and prairie dogs. Many people keep rodents such as mice, rats, guinea pigs, and hamsters as pets. Rodents reproduce frequently and usually have many offspring. Some mammals that are like rodents are rabbits and shrews.
Some mammals spend most or all of their lives in water. For example, beavers live both on land and in the water while manatees live their whole life in the water. Hippos, or hippopotamuses, are a large animal with thick, gray skin like an elephant. Their eyes, ears, and nostrils are located high on their heads so the hippo can stay deep in the water for long periods of time. Hippos do this to stay cool and avoid getting sunburned. Otters are furry mammals that eat fish and mollusks in rivers and the ocean. They float on their backs and break open shells with rocks. Beavers are furry rodents that use branches to make dams across rivers. They build homes that they enter from underwater.
Seals, sea lions and walruses. Seals, sea lions and walruses have webbed flippers to help them swim in the ocean. They can move on land, but are clumsy and slow. They spend time lying around on beaches or rocks. Seals and sea lions eat fish while walrus eat clams, snails, crabs, and worms. Walruses have long tusks.
Whales and dolphins. Whales and dolphins cannot live on land. They live in the ocean and must come to the surface to breathe air. A whale or dolphin breathes through a nostril on its back called a blowhole. The blue whale is the largest animal in the world.