University of Minnesota

If There is No Milkweed, Where Will Monarch Butterflies Lay Their Eggs?

Elissa Cusmia and Giulia Rocca
Willow Creek Middle School
Rochester, MN


We put 10 female butterflies in a tent with no milkweed. Instead, we gave them an assortment of egg-laying surfaces: light green paper, dark green paper, and green plastic. All of these were cut in the shape of milkweed leaves. Some of each kind were rubbed with milkweed latex, others were plain. We attached the fake leaves to a branch with clothespins. The purpose was to find out what they would lay their eggs on if there wasn't real milkweed. They didn't pick any of the fake leaves. They laid their eggs on the sides of the tent and on feeding sponges instead! We learned that it was not so easy to fool the butterflies, and that they will lay their eggs, but not on fake leaves.


We observed that our classroom's monarchs not only laid eggs on milkweed, but on the tent wall as well.


If there is no milkweed, where will the female monarchs lay their eggs?


Our class split into groups and each group came up with one hypothesis. Here are some of our most eligible hypotheses:

  • the females will lay no eggs;
  • they will lay eggs on another plant,
  • on the side of the tent,
  • on green paper,
  • plastic or fabric leaves,
  • one rubbed with milkweed latex,
  • or one without.


To start this experiment, we observed females that were laying eggs in the big tent. We took ten females and put them in a smaller cage where we would be able to observe them better. In the cage, we put a begonia plant and a twig with leaves made of green plastic, neon green paper, and dark green paper. There were two of each leaf and one of the two leaves was rubbed with milkweed latex while the other was not. We also put two artificial leaves on the plant but neither was rubbed with latex. For food, we gave the females a plastic petri dish which contained three sponges. Every day during Life Science class, we would check the cage for eggs and count them. We started October 27, 1998 and recorded this data on a spreadsheet through November 20, 1998. When we checked the tent for eggs, we looked at all the walls and other locations and recorded these results in the spreadsheet as well. One day we even found a larva on the paper towel, he really blended in! One unusual place where we found many eggs was on the petri dish.


The females main laying surfaces were the wall and the plastic sponge cup. The females also laid eggs on the paper towel (we kept this on the floor to keep the cage clean), the side wood (rim on the tent), and the food sponges.


With no milkweed to lay their eggs on, the female monarchs laid the most live eggs on the plastic sponge cup and the most infertile eggs on the wall (netting) of the cage.

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