How do we know?
↻ One of the pages with a moving picture
Scientists opened a chrysalis at just the right time.
- A monarch lays eggs on milkweed leaves. They hatch in about four days.
- The caterpillar eats and eats. It grows from under 1 cm to about 5 cm, shedding its skin.
- Inside its chrysalis, it digests itself into a kind of soup! Special groups of cells survive.
- Those cells build wings, eyes and antennae. Then the adult butterfly climbs out.
Scientists carefully opened a chrysalis at just the right time. Out came soup! But some nerves and muscles were still there.
A caterpillar and its butterfly are the same animal. It changes body shape completely.
Monarchs travel in huge crowds. Every fall, millions of monarchs crowd onto trees in a reserve in Mexico, bending the branches.
Wow number
100 to 300 A female monarch butterfly lays 100 to 300 eggs in her life.
Myth or fact?
A caterpillar and its butterfly are the same animal. Fact. It changes body shape completely.
Monarch caterpillars eat any kind of leaf. Myth. Monarchs lay their eggs on milkweed.
Think about it
Why might it help a caterpillar to look so different from a butterfly?
Where in the world?
Monarch reserve, Mexico where, every fall, millions of monarchs crowd onto trees, bending the branches — 19.5667° N, 100.2833° W.
Where these facts come from
Every number on page 57, and who measured it
This page tells us about the monarch's four life stages and its milkweed food.
Monarch Butterfly Biology — The U.S. Forest Service
fs.usda.gov/wildflowers/pollinators/Monarch_Butterfly/biology/index.shtml
We checked it on 31 October 2026
This page explains what happens inside a chrysalis.
How Does a Caterpillar Turn into a Butterfly? — Scientific American, a science magazine
scientificamerican.com/article/caterpillar-butterfly-metamorphosis-explainer
We checked it on 31 October 2026
This page tells us about the monarch forests in Mexico.
Monarch Butterfly Biosphere Reserve — UNESCO World Heritage, the United Nations' list of the world's most special places
whc.unesco.org/en/list/1290
We checked it on 31 October 2026
Has this changed?
How a caterpillar becomes a butterfly is not going to change.
What changes is how closely scientists can look inside the chrysalis.
Words from this page
- milkweed
- The plant that monarch caterpillars eat.
- chrysalis
- The hard case a caterpillar makes before it becomes a butterfly.
- antenna
- One of the two feelers on a butterfly’s head. The plural is antennae.
Try it!
Make a life-cycle wheel.
1. Draw lines to split a paper plate into four parts. 2. Draw egg, caterpillar, chrysalis and butterfly, one in each part. 3. Add arrows going around in a circle.
What happens: you made a cycle. The butterfly lays eggs, and it all starts again!
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