Monarch Butterflies

All About Monarchs

The monarch butterfly (Danaus plexippus) is a beautiful winged insect that measures about 90 to 100mm from wingtip to wingtip. Monarch butterflies are indigenous to Canada, the United States, Mexico, and Central and South America. They live in the Philippines, Australia, New Zealand, southern Europe, and northwest Africa, although they are not native to these places.

Each fall as many as 100 million monarch butterflies migrate from the northern parts of North America to California and Mexico. Monarch butterflies are not an endangered species, but threats such as habitat loss are an important concern. 

The Royal Family of the Butterfly World

Monarch Butterfly

Monarch butterflies are sometimes called milkweed butterflies because it is one of their favorite foods.  The caterpillars love the leaves and the adults like the nectar in the flowers.


The word monarch means king or queen. In fact, the early settlers of North America called monarch butterflies “King Billys,” after William of Orange, who became king of England in 1689. Monarch butterflies are also sometimes called milkweed butterflies. In Australia and New Zealand, people call them wanderers.

Monarch Hang Outs


Monarchs like to spend the summer in warm places where many flowers grow.


In North America, monarch butterflies spend the summer months in habitats where milkweed and other flowers grow. This is because monarch caterpillars eat milkweed leaves and adult butterflies feed on nectar from flowers. Typical monarch habitats include fields, meadows, gardens, prairies, wetlands, and roadsides.

In winter, monarchs from east of the Rocky Mountains overwinter in forests in the state of Michoacán in central Mexico. Monarchs west of the Rockies stay in forests along the California coast.

Big Changes, Short Lives

Like all butterflies, monarchs undergo a metamorphosis. They start life as an egg. A caterpillar hatches from the egg. After about two weeks, the caterpillar sheds its exoskeleton and hardens into a chrysalis. Changes take place inside the chrysalis. These changes turn the chubby, wingless caterpillar into a dainty, winged monarch butterfly.

Four to five generations of North American monarchs hatch each spring and summer. Most live only two to five weeks, but the last generation of the summer lives six to seven months. It is this generation that makes the long migration to the overwintering sites.

4 Wings and 6 Legs


You may not have monarch butterflies where you live but go outside and take a good look at the anatomy of different butterflies, many of them look very similar.

©Jacob Boyd (top); Edith Smith (bottom)

Monarch butterflies are insects, which makes them members of the arthropod phylum. They have four wings, two in the front and two in the back. The wings are covered with thousands of tiny scales. These scales are what give the monarch its bright orange, black, and white pattern. Between the wings are the main parts of the body: six legs, the abdomen, thorax, and head. 

Love That Nectar

Monarchs are plant eaters, or herbivores. Monarch caterpillars and adult butterflies spend most of the spring and summer looking for and eating food. As caterpillars, they eat only milkweed leaves. Adult monarchs drink nectar from milkweed and other wildflowers, such as goldenrod, clover, thistle, and purple coneflower. They also like to drink nectar from garden flowers such as sunflowers, cosmos, zinnias, and marigolds.  

Milkweed: Birds Beware!


Milkweed leaves contain a poisonous chemical which makes monarch caterpillars taste gross to birds.


The milkweed the caterpillars eat is a secret weapon – a deadly one. It contains a poisonous chemical, which the caterpillars store in their bodies. The chemical stays with them even as adults.  This poison doesn’t harm the monarchs, but it makes them taste terrible to certain predators, such as birds. This is a defense adaptation. Their brilliant markings are another adaptation. The markings warn predators that they don’t taste good.


Milkweed poison does not affect spiders, wasps and other predators that eat monarch caterpillars.

©Edith Smith

For these reasons, most birds avoid eating monarch caterpillars and adult butterflies. In fact, birds who have tried eating a monarch never do so again. In one scientific study, birds that had tasted monarchs began throwing up if they even glimpsed a monarch butterfly!

But milkweed poison doesn’t bother other predators. Spiders, assassin bugs, stinkbugs, and wasps will all attack and eat monarch caterpillars anyway. Fire ants are a big problem for monarchs in Texas. They eat monarch eggs and will swarm large monarch caterpillars and kill them.

A Long Journey South

Monarch butterflies are thought to be the only species of butterfly that migrates between a summer habitat and a winter habitat. Scientists believe that the changes in daylight and temperature at the end of summer signal to monarchs that it is time to move.

Most monarchs begin their journeys in September and October. They travel along the same migration routes year after year. Large flocks start to form as they get closer to their over-wintering sites.

Gliding and Rest Stops

Along the way, they seek out thermals, or columns of warm air, to give them a lift and help them glide. They stop often to feed on nectar and to drink water. They also stop every night and during storms. Often, many butterflies will gather in one place, usually on a tree.


Monarchs on tree

During migration, large groups of monarchs take shelter in trees, often covering the entire tree in butterflies.

©F.Lanting/Minden Pictures

Monarchs in western North America migrate to about 25 sites on the coast of California. There they take shelter in eucalyptus, pine, and cypress trees.
Monarchs from east of the Rocky Mountains fly up to 3,500 km south to Mexico. Their journeys can take as long as 90 days. They go to about 14 forested sites where they roost on oyamel firs and cypress trees. A single tree may have thousands of butterflies on it. These large groupings of butterflies are known as aggregations (ag-ri-GEY-shuhns).

Staying Alive Through the Winter

Monarchs in cold weather

When the weather gets too cold, monarchs are unable to fly and they struggle just to stay alive.

©Edith Smith

During the winter the main job of the monarchs is to stay alive. The aggregations cling to the trees for protection from weather, to help stay warm, and to keep from drying out. Temperatures at the sites range from 6 ° C to 15 ° C. The cool temperatures slow down the monarchs’ body processes and help them use less water and energy. Monarchs are unable to fly when the temperature is below 13 ° C, so there are many days when they simply stay put. They live off the fat and water stored in their abdomens.

A Long Journey Back North

Monarch eggs

Female monarchs lay eggs that hatch into caterpillars.

©Edith Smith

Toward the end of winter, temperatures rise and the days get longer. If it is a warm day, monarchs may leave their roosts to find water or nectar. Males and females begin mating. Starting in February and March, the monarchs start migrating back to their summer habitat. As they retrace their route, the females lay eggs on newly sprouted milkweed plants. These eggs hatch into caterpillars, which become the next generation of monarch butterflies. These new monarchs continue migrating, also laying eggs and starting new generations of monarchs.

Monarchs under Threat

Monarch butterflies are not an endangered species. However, their yearly migration is considered an endangered phenomenon. Over the years, their over-wintering habitats have been damaged and lost as the land is logged and cleared for homes and farms. That means there are fewer places for monarchs to roost in the winter.

Monarchs face other threats, like losing their food supply. In many places, people use chemicals to kill milkweed and other plants that grow wild. Plus, undeveloped land where milkweed grows is being cleared for houses and shopping centers. So there are fewer milkweed plants for adult monarchs to lay eggs on, and for caterpillars to eat. Some scientists also believe that chemicals used to kill pests such as mosquitoes and gypsy moths are harming and killing monarch caterpillars and adults.

Protecting Monarchs and Their Habitat

In California, lawmakers have passed laws to protect some of the monarch habitat. Mexico’s government has also passed laws that set aside some of the sites in the oyamel forests as monarch sanctuaries. This has helped, but illegal logging in Mexico still goes on. People need the money they can make by logging. Local leaders are working to find other ways for people to make a living that will not harm monarch habitat.


Logging is one of the threats to monarch habitats.

©F.Lanting/Minden Pictures

Getting governments to set up monarch sanctuaries is one big step. But there are important steps that communities and individuals can take. The monarch butterfly conservation group, Monarch Watch, encourages people in North America to create “Monarch Waystations” in gardens, parks, and elsewhere along monarch migration routes. These waystations are areas planted with milkweed and flowers that provide food, water, and shelter for monarchs as they travel to and from their over-wintering sites.

Are monarch waystations being created near you? Ask your teacher if your class can investigate.