Milkweed Butterflies

Milkweeds are so named because the eggs are usually laid on foliage of milkweeds and the larvae feed chiefly on these plants. The most common species is the monarch. It has a wingspread of up to about four inches (102 mm). Large numbers of monarchs fly south for the winter and return north in the spring. The queen, another common milkweed butterfly, has a wingspread of about three inches (76 mm). Milkweed butterflies are of no economic importance.

Family: Danaidae. The monarch is Danaus plexippus, or D. archippus; the queen, D. gilippus.

Butterflies live all around the world. They depend on plants for food, so they cannot live in frozen Antarctica. But, butterflies can be found on all other continents and on most islands.

Hundreds of years ago, monarch butterflies lived only in North America and South America. Over time, however, monarchs spread across the Pacific Ocean to Hawaii, New Zealand, Australia, and Indonesia. They also spread across the Atlantic Ocean to the Canary Islands and parts of Europe.

How might monarchs have spread around the world? They could have “hitched” rides on the many ships that travel back and forth between continents. Once in their new homes, the female butterflies might have laid eggs. Then, over time, the population of these newly transplanted insects could increase greatly.

Monarchs can live as far north as Canada. But they cannot survive cold winters. So monarchs that live in cold places must migrate (MY grayt), or travel, to warmer places before winter.

In the fall, monarchs hatched in cooler regions migrate as far as 2,000 miles (3,200 kilometers) before winter starts. By late fall, they come to rest primarily in parts of California and Mexico, where they form huge colonies for the winter. In spring, shortly before dying, they begin flying north and east. They lay eggs along the way, typically in northern Mexico and the southern United States.

While the migratory monarchs live more than six months, their offspring generally live a few months or less. These offspring, and successive generations, move further north over the summer, laying eggs along the way. By the next fall, another generation of monarchs is born that will migrate to the warmer regions for winter—places where these monarchs have never been. Scientists do not fully understand how migrating monarchs “know” where to go.

Some butterflies hibernate (HY buhr nayt) during cold winter weather. The mourning cloak is one such butterfly.

In the fall, when the days are getting cool, the mourning cloak searches for a sheltered place. It snuggles into a pile of leaves under a log, a small crack in a brick wall, or some other cozy spot. Then the butterfly makes a special chemical in its body that keeps its blood from freezing.

When the days grow warmer in spring, the mourning cloak wakes up and begins to shiver. Shivering produces heat inside the butterfly’s body. Soon, the mourning cloak is ready to fly away.

Many other kinds of butterflies hibernate, as well. Like the mourning cloak, they wake up as winter turns to spring.

A monarch’s wings are made up of thousands of tiny, thin, flat scales. Each scale has its own special color. The scales fit together to form a beautiful, complex pattern.

Other butterflies’ wings are made of scales, too. And, so are moths’ wings. No other type of insect has wing scales like those of butterflies and moths.

That is why the wings of flies, bees, and other insects are clear or much less colorful.

What colors can butterfly wings be? They can be black, white, gray, brown, tan, red, orange, and yellow. They also can be bright shades of blue, purple, and green.

To birds, frogs, spiders, and other animals that eat insects, a butterfly looks like dinner.

The monarch, however, protects itself by tasting bad to predators. When a bird takes a bite out of a monarch, the bird gets sick. Birds remember the bright pattern of a monarch’s wing. A bird that gets sick from tasting one monarch probably won’t try to eat another.

Monarch butterflies taste bad because monarch caterpillars eat milkweed plants. For most creatures, eating milkweed results in vomiting or even death. Protective chemicals that the caterpillar obtains by eating the milkweed remain with it through its metamorphosis into a butterfly. The bitter or poisonous juices of the milkweed plant are stored in the adult monarch’s tissues, making the insect taste bad.

Viceroy butterflies have wings that look like monarch wings. Viceroys aren’t the least bit poisonous. But birds think they are distasteful monarchs, and so they stay away.