Although some students may already know that monarch caterpillars only eat milkweed, it is worth letting students investigate this and prove to themselves that monarchs are indeed "specialists" on milkweed. For further background on feeding larvae, see Monarch Butterfly Rearing and Observing Techniques in the HOW TO section. There is also additional background on milkweed species in the Monarch Biology section.

Materials

• Several 4th or 5th instar caterpillars
• Choices of food (ask students to bring in food from home that they think the caterpillar may eat, examples may include apples, chips, cheese, tree leaves, grass, bread)
• Milkweed leaves (more than one kind if available)
• Paper plates
• Chart paper

Procedures

Guide your students through the following steps of the scientific method. They may come up with alternative hypotheses, methods, and results. Those we’ve listed here are only examples.

Question: What do monarch caterpillars eat?

Hypothesis: Monarch caterpillars eat only milkweed.

Methods:

1. Place one kind of food on a paper plate, and place a caterpillar on the food. Watch to see if the caterpillar eats it.
2. Have one student time the caterpillar, allowing it 2 minutes (or some other set time) to find and/or eat the food. If they can, students should make notes of behaviors (e.g.: searching, crawling away from food) for later discussion. If your students can’t write, have them tell you what the caterpillar is doing, and keep a list of behaviors.
3. Define food preference as whether or not the caterpillar actually ate some of the food. Repeat with all of the different types of foods. You may want to switch caterpillars to avoid stressing one individual. You may also want to set up two plates at a time.
4. Record caterpillar food preferences on a chart as below.

Sample Results:

Food	Eaten (Yes/No)
apple maple leaf cracker common milkweed swamp milkweed	no no no yes yes

ã 2000 Monarchs in the Classroom  - University of Minnesota
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