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. People often wonder:
- Will there be enough milkweed for the hungry caterpillars?
Here's an experiment you can try to measure how quickly milkweed grows, and how much milkweed a monarch needs as it grows:
1) Find
Some Milkweed
Watch for a milkweed plant to emerge this spring.
2) Measure its Leaves
When its first leaves appear, measure the surface area of each leaf.
(To do this, make a grid by photocopying graph paper onto a clear transparency.
Look through the grid and count the surface area of the leaf.)
3)
Make a Milkweed Growth Chart
On a sheet of paper, make a three-column chart:
| Milkweed
Growth Chart |
||
| Date |
Number
of Leaves |
Surface
Area of Leaves |
4)
Observe the Milkweed Every Day
As the plant grows, record the amount of milkweed that's available each
day. If you have a digital camera, take pictures of the milkweed each
day so you have a visual record.
5) Watch a Caterpillar Grow
Next find a monarch egg. As soon as it hatches, measure how much milkweed
the larva eats. It will take from 9-14 days to develop from an egg to
a chrysalis. Again, photographs would be an excellent way to document
changes in the growing milkweed and caterpillar.
| Caterpillar
Growth Chart |
||
| Date |
Stage
of Growth |
Area of Leaves Eaten |
Tip: To learn about the stages of caterpillar growth, and to estimate the time it will take your caterpillar to grow, see: Caterpillar Growth Calendar
6) Summarize Your Results
- How much milkweed can one larva consume in its days of eating?
- How many days does it take for milkweed to grow enough plant material to meet one larva's needs?
- What factors seem to affect the rate the milkweed grew? the caterpillar?
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