Which Grows Faster, a Monarch or a Milkweed Plant?


Monarchs often arrive in the spring just as milkweed is emerging from the ground. When milkweed is in short supply, a monarch may lay more than one egg per plant. "Egg loading" is a sign that milkweed is in short supply. If milkweed were plentiful, monarchs would not lay so many eggs on a single plant.

When people see milkweed plants loaded with eggs, they wonder:

  • Will there be enough milkweed for the hungry caterpillars?

The Annual Cycle of the Monarch Butterfly


1. Introduce students to this topic by discussing the images and questions on the Journal Page.

2. Watch this Video Clip of a hungry caterpillar, and share background facts: It took only 20 minutes for this monarch to consume the leaf he was standing upon. He ate 3 leaves the afternoon of his filming!

3. View and discuss the slideshow, Can a Milkweed Plant Grow Fast Enough?

Journal: Can milkweed grow fast enough to feed hungry larvae?
Journal Page

Dr. Karen Oberhauser
Video Clip

Try It! Document the Growth of Milkweed and Monarchs

1. Find a Milkweed Plant
As milkweed plants emerge in the spring, select a plant to study. Plan to take pictures to show how quickly the plant and leaves grow.

2. Measure Milkweed Growth
When the first leaves appear, measure the surface area of each leaf by photocopying graph paper onto a clear transparency. Look through the grid and count the surface area of the leaf. Record the measurement data on the Milkweed and Caterpillar Growth Chart.

3. Find a Monarch Egg and Document Changes
When the monarch egg hatches, observe and estimate how much milkweed the larva eats. Document growth of the caterpillar and area of milkweed consumed on the chart.

Tip: For practical reasons, it's difficult to raise monarch larvae in outdoor conditions. If you raise your caterpillar indoors, keep the temperatures as close to outdoor conditions as possible. Rate of growth of milkweed and larvae is dependent on temperatures.

4. Summarize Your Results

  • How much milkweed did one larva consume during its caterpillar stage? (number of leaves, area of leaves)
  • Based on your data, how many monarch larvae would your milkweed plant feed?

5. Please Share Your Results!
Your observations have scientific value. Please contact Journey North if you would like to share your photo study and data.


Milkweed and Monarch Growth Chart

Milkweed and Caterpillar Growth Chart