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A snake slithers up a saguaro cactus. A gray bird sits on one of the cactus's arms. The bird doesn't see the snake. The snake moves closer. Suddenly, it strikes. With a flutter and a flap, the bird flies off. The snake has missed its meal.

The bird will return. So will the snake. Both animals need this cactus.

A saguaro cactus can live for about 150 years. Throughout its life, animals will come to it. They will use it for food, shelter, and water. Birds will nest in it. Animals will eat its fruit. In the hot, dry desert, a saguaro cactus is the center of life.

The saguaro doesn't start out this way. During its first 10 years, it hardly grows at all. That's because a desert is hot and dry.

Not many kinds of plants grow in a desert ecosystem. Luckily, the cactus has adaptations that help it survive. It's built to live in the desert.

One adaptation is its skin. The skin is thick and waxy. It traps and holds water, so the cactus won't dry up.

Rows of sharp spines are another adaptation. They line the stem and protect the water inside. They keep animals from taking juicy bites.

The saguaro's roots also help it survive. They hold the cactus in the ground. They soak up water, too.

The roots don't grow deep. That's a good thing when it rains. As soon as water soaks into the ground, the roots slurp it up.

The cactus stores water in its stem. During rainstorms, the cactus sucks up as much water as it can. The stem gets fatter.

On hot, dry days, the saguaro takes water from its stem. You can tell when its water supply is low. The saguaro gets skinny.

A saguaro makes its own food. At night, tiny holes on its stem open. Carbon dioxide (CO2), a gas in air, flows into the holes.

During the day, the cactus takes in energy from the sun. That energy, the water, and the CO2 mix together. That makes plant food. This process is called photosynthesis.

The cactus uses food and water to make flowers. Its white flowers open at night. Bats and doves come to sip the nectar. They have to work fast. The flowers close during the day.

In late June, the flowers dry up. Fat fruit grow in their place. The fruit look like spiky red crowns. They split open under the sizzling sun. Insects and birds feed on the sweet pulp.

Some fruit fall to the ground. Javelinas, which look like hogs, come to eat the fruit. Their strong jaws and tusks tear into the pulp.

After the javelinas, other animals come. For example, squirrels and rats eat the leftovers. Then mice and rabbits gobble up the black seeds.

Not all animals eat the saguaro. Some live in it. A mother Gila woodpecker makes her home in it. Tap, tap, tap. She pecks a deep hole in the skin. The dark hole makes a cool nesting place.

She lays her eggs and raises her chicks here. Soon the chicks are able to fly. The birds move on.

An elf owl might move in next. It may stay for years. The hole is safe. From here, the little owl can spot prey.

In time, the saguaro is full of life. Branches grow out from its sides. Hawks nest in the crook of these arms. Animals eat the plants growing in the saguaro's shade. A bobcat sits on top. Up here, it can watch for predators like coyotes.

For 150 years, the cactus is a good habitat. Then old age and disease weaken it. One rainy night, a bolt of lightning strikes it. With a crash, it falls to the ground.

Yet animals still visit. Scorpions creep into it. Rattlesnakes slither around it. A jackrabbit sips at a root filled with water.

The saguaro will soon rot away. Yet other saguaros still grow nearby. Life in the desert goes on.

Article by Barbara Seeber.