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A project of the Chicago Botanic Garden


Milkweeds and Monarchs

Summer 2020 - Fall 2025

Help preserve the majestic monarch butterfly

Soaring from Mexico into the United States and Canada, monarch butterflies are searching for one thing: milkweed plants. Monarch butterflies are beautiful, charismatic insects known for their long-distance migration and their reliance on milkweeds (Asclepias species). Milkweeds are the only plants on which monarchs lay their eggs. After the eggs hatch, the caterpillars, also called larvae, eat milkweed leaves to grow. However, over the last 20 years, the number of monarch butterflies in North America has dropped, and one possible cause is a lack of milkweed plants. As efforts to plant more milkweeds are growing, researchers are studying the relationship between milkweeds and monarchs more closely. Some scientists have found preliminary evidence that monarchs prefer to lay eggs on young milkweeds that have not yet started to flower.


Do monarch butterflies prefer to lay eggs on flowering or non-flowering milkweed stems?

If monarchs prefer younger, non-flowering plants, scientists can do further experiments to determine why. Perhaps younger plants are easier for the developing caterpillars to eat, or maybe flowering plants attract predators of monarch eggs and caterpillars? Indeed, a number of different insects like ants and beetles, as well as spiders are known to eat eggs and small caterpillars. If data shows that monarchs lay more eggs on non-flowering plants, managing milkweed patches, though mowing or cutting back the plants, may help support monarchs and lessen the declines. Let’s find out, shall we?

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How to Participate

Create or log into your Budburst Account and submit a pollinator observation.

Report using your handheld device or record your observations on a printable datasheet and add your findings online later.


Anywhere that milkweeds grow and monarchs are present. You can observe any of the 12 species of milkweed for this project by searching Asclepias here.



Find a milkweed patch to monitor

You can start monitoring when at least one plant is flowering. If you have landowner permission, cut back some of the milkweed plants to prevent them from flowering. Have about half flowering and half non-flowering phenophases in your patch.


Learn what monarch eggs and caterpillars look like

Monarch caterpillars, also called larvae, go through 5 stages or “instars” before they cocoon and become a butterfly. Below is a guide to the eggs and instars.


Gather your materials

Datasheets, milkweed and monarch identification materials are downloadable below. If possible, use a magnifying glass or hand lens.

Each time you monitor, you will record the following data:
  • The approximate number of milkweed plants in your patch

  • How many plants are flowering and how many are non-flowering

  • How many open flower clusters are on each plant

  • How many eggs you see on each plant

  • How many first instar larvae you see on each plant

  • How many later instar larvae you see in each plant

  • Whether or not any other insects or spiders are present on each plant (like ants, beetles, aphids, spiders)

Related Resources

  1. Milkweeds and Monarchs Basic Data Sheet
  2. Monarch Eggs and Instars Guide
  3. Milkweed Identification Guide
  4. Insect Guide
  5. Data Collection Guide
  6. Project Vocabulary
  7. More Information
  8. Milkweeds and Monarchs Advanced Data Sheet

Migration Monitor

Follow the monarch migration through North America by keeping an eye on local milkweeds during spring and summer.

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