Scientists think that pet dogs descended from wolves thousands of years ago. The bodies of wolves and pet dogs are still much alike in shape, although wolves are larger and heavier than most dogs. A male adult wolf is about 2 1/2 feet (76 centimeters) tall at the shoulder. A male weighs about 75 to 120 pounds (34 to 54 kilograms). Female wolves are slightly smaller than males.

All members of the dog family, including wolves, run on the fronts of their paws. Most members have five toes on each front paw and four on each back paw. One of the front toes, the dewclaw, does not touch the ground. It is located on the back of the paw.

Wolves and pet dogs are both social animals and good communicators. Most pet dogs are friendly to each other and to humans. Wolves are friendly toward other pack members. But just as most pet dogs guard their homes, wolves protect their territory. Like pet dogs, wolves have a playful side, too.

Wolves don’t have easy lives. Often they have to travel many miles to find prey. And most wolves don’t catch every animal they hunt. Their prey have strong defenses. Deer and caribou can run faster than wolves. Huge musk oxen fight off wolves by standing in a circle with their horns facing out.

To help them catch prey, wolves live and hunt in packs of 8 to 12 members. Each pack stakes out a large territory as its hunting ground. Wolves mark the territory by urinating along its border. They fiercely defend the territory against other wolf packs. The territory is important because it’s where adult wolves find food for themselves and their young.

Large packs of wolves can more easily capture large prey. For example, a large pack might attack a moose rather than a deer. Pack hunting is especially important when pups are born. A litter of pups may need more meat than two parents alone can provide.

Each pack has a dominant male wolf that is the leader. This wolf is called the alpha male. The alpha male helps keep order among the pack members. He also leads the hunt. Being in charge has its rewards, too. The dominant wolves always eat first after a kill.

Other pack members often include the alpha male’s mate (called the alpha female), their pups, and the alpha male’s brothers and sisters.

When pack members meet the leader, they use body language to show their respect. They crouch down with their ears flattened and tails low. This is their way of saying, “You are the leader.”

Members of a wolf pack also have a greeting ceremony. This takes place just before or after a hunt. The wolves wag tails and lick one another’s faces. They rush to the leader and show their loyalty by sticking their muzzles in his face.

Wolves have several features that help them hunt prey. Wolves have excellent hearing. They also have a keen sense of smell. Wolves can smell a deer from over 1 mile (1.6 kilometers) away.

Wolves have very good eyesight, too. A wolf’s eyes are in the front of its head. A wolf can see its prey with both eyes at once. Its vision in the dark is very good, and it can easily spot movement.

Wolves have long legs that help them run fast. A wolf can run for 12 miles at 15 to 30 miles (24 to 48 kilometers) per hour. Over a short distance, it can sprint as fast as 40 miles (64 kilometers) per hour.

Wolves use their sharp canine teeth to hold onto prey. Wolves have very strong jaws that can crunch the huge bones of moose and other large prey.

Wolves usually hunt in a pack. This makes them more efficient hunters. Each hunt may take several hours. As the wolves set out, they often run in a single line to search for prey.

The wolves may find a herd of caribou or musk oxen. The pack will usually choose a weak or old animal as its prey. Such an animal is almost always easier to catch than a young, healthy one. The wolves then sneak toward the animal. They stay downwind so that the prey cannot smell them. Once they are close, the wolves start to run. They attack the animal’s rump or sides. As the animal weakens and stumbles, the wolves grab it by the throat or snout. Then they quickly kill it.

Pack members work well together. Some wolves may distract a mother animal while the others sneak up on her young. Or a few wolves may go ahead of the pack and hide. They ambush the prey when the rest of the pack drives it toward them.

Wolves howl for many reasons. Sometimes, wolves howl to claim their territory. Their howls warn other wolves to stay away. On a calm night, their howling can be heard from up to 10 miles (16 kilometers) away. Sometimes one pack howls, saying “This is our territory.” Other packs howl back, saying “This is ours.”

Howling helps pack members keep in touch when they get separated. It also helps them get together again. No two wolves have exactly the same voice. When they are separated, wolves probably recognize one another’s howls, just as we recognize the voices of our friends on the telephone.

Wolves also howl just because they like to. Some people think the howls of wolves sound a lot like a group sing-along. Howling together helps keep up a strong group feeling in a pack.

Wolves have many ways to communicate with one another. One way is with sounds. In addition to howling, wolves use a variety of other sounds to “talk” to each other. An alpha wolf may growl at another wolf. The other wolf may whine or squeal.

Wolves also use body language. For example, a wolf may crouch down before the pack leader. Or a wolf may signal “Let’s play!” with forelegs down, rump up, and tail wagging—just as a pet dog does.

Wolves also use their tails to communicate their status in the pack. A wolf may curl its tail under its body when it is with the alpha wolf.

Wolves sometimes show feelings with their faces. They make threatening or “Don’t hurt me” expressions. Good communications among pack members helps keep order and enables the pack to work together successfully.

Usually only the alpha male and female in a wolf pack breed. They mate in winter. Then the female prepares a den. She may take over an old fox’s den. Or she may dig a new den in a sandy hillside near a stream or lake. The tunnel leading into the den may be 15 feet (4.5 meters) long.

After two months, the female gives birth to a litter of from 1 to 11 pups. A newborn wolf pup is blind, deaf, and helpless. It needs its mother’s warmth to keep a steady body temperature. The pups spend their first days living in the den and drinking their mother’s milk.

After three weeks, the pups begin to explore outside and to eat meat. They beg for meat by licking the lips of their mother or another adult wolf. The adult coughs up some of the meat it has recently eaten, and the pups eat it.

A pup-sitter watches over the pups while the mother goes hunting. The pup-sitter is usually a “lower-class” member of the pack. The sitter may be a brother or a sister from the previous year’s litter. Or the sitter may be an inexperienced hunter.

Through the summer, the den is a center of activity for the pack. The adults go off to hunt in the evening, as a pack or in small groups. When the hunters come back in the morning, the pups mob them and beg for food. The pup-sitter may also beg for food.

When they are 2 months old, the pups no longer need the den. The pack relocates to an open-air home called a rendezvous (RAHN deh voo) site, or meeting place.

Wolf pups chase, wrestle, and pounce on one another. They play with objects they find, too. As they win or lose at play fights, they work out a dominance order among themselves. The winners of play fights make it clear that they are more powerful than the losers are. Winning at play shows that they can dominate their less powerful brothers and sisters.

Playing also helps pups develop their muscles and practice the skills they will need for hunting. They sneak up and pounce on insects and small animals. At first, the pups often miss. But they are quick learners.

In the fall, the pups and adults begin to hunt together. The pups learn by watching the older wolves. It takes time and practice for a young wolf to become a skilled hunter.

The white fur of the Arctic wolf blends with the snowy background. This makes it difficult for the wolf’s prey to see it coming.

The fur of an Arctic wolf is very thick. It needs to be! In winter, temperatures in the Arctic can drop to -70 °F (-57 °C). To stay warm, Arctic wolves grow an extra layer of fur in winter. This makes their legs look very thick. At night, the wolf curls up with its legs close to its warm body. It wraps its fluffy tail over its face.

Arctic wolves are not born white. Pups are usually born after the snow melts. Newborn pups are a gray-brown color. This helps camouflage, or hide, them during their first summer. It’s a good thing, too, because some birds of prey and other animals kill and eat these pups.

Sometimes, wolves do leave their packs. A wolf may leave because it has been mistreated by other members. An alpha wolf might go off on its own if it has been replaced by a new alpha wolf.

Living alone can be very dangerous for a wolf. A lone wolf must be careful if it wanders into the territories of wolf packs. Wolf packs may chase the lone wolf off. The packs may even fight the lone wolf and kill it. A lone wolf must also find and kill enough food by itself. This is often very difficult.

If everything goes well, a lone wolf will eventually find a mate. Together, the two may even form a pack and establish a territory of their own.

Wolves belong to the family Canidae. The gray wolf is Canis lupus; the Mexican wolf, C. l. baileyi; the red wolf, C. rufus.