Butterflies have complete metamorphosis. This means the young look completely different from the adults. Inside the chrysalis, the caterpillar's body breaks down. It is rebuilt as a butterfly. A butterfly pupa is called a chrysalis. A caterpillar sheds its skin as it gets bigger. This is called molting. A grown-up butterfly does not get any bigger.
A monarch caterpillar grows through five stages, called instars. It sheds its skin between them. It grows from a few millimeters long to about two inches (5 cm). This is before it makes its chrysalis. A caterpillar fastens itself with silk to a stem or twig. The silk is either a pad or a girdle. Many caterpillars hang upside down from a button of silk just before they become a chrysalis.
A butterfly's large compound eyes let it see in almost every direction at once. Butterflies taste with their feet. Monarch caterpillars eat milkweed. Milkweed is poison to most animals. The poison stays in the monarch's body. It makes the monarch taste bad. A monarch's bright colors warn birds that it tastes bad. The viceroy butterfly copies the orange-and-black look of bad-tasting butterflies like the monarch and queen.
Some butterflies spend the winter asleep as an egg, caterpillar, chrysalis or adult. Monarchs cannot live through cold northern winters, so they fly south. Monarchs east of the Rocky Mountains spend winter in Mexico. Some monarchs fly as far as 3,000 miles. The monarchs that fly to Mexico have never been there before. Yet they find the way. Monarchs use the sun to stay on course. They have a backup compass for cloudy days.
Forests where monarchs spend the winter are shrinking. This is because of cutting of trees, storms and building. Mexico protects the mountain forests where monarchs spend the winter. They are in the Monarch Butterfly Biosphere Reserve. As of November 2026, there are far fewer monarchs now than there used to be. Monarchs have fewer places to lay eggs. This is because milkweed has been lost from many fields and roadsides. Scientists and volunteers tag monarchs and track them to learn about their travels.
Words to know
- instars: growth stages
- girdle: silk loop
