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Background

In this experiment, students will determine how much monarch larvae eat, using the skills of observation, prediction, measurement, recording data, analyzing data and reporting. Furthermore, they will gain experience in the skills of estimation and the use of percent.

Before doing this lesson, be sure to read Rearing Techniques in the HOW-TO’S section. Start the lesson a day or so after you obtain the larvae. Part 1 should be done on the first day and part 2 starts the second day of the lesson and can be repeated daily until larvae pupate, if desired. You should use an individual container for each larva. Larvae can be kept in clear plastic cups with lids for several days without harm. If lids are tight, punch holes to allow airflow. This lesson will not work with late fifth instar larvae (i.e. those that are about to form a chrysalis), since they stop eating at that time. Also, when larvae are molting (shedding their skin) they often stop eating for a day. This will be interesting for students to observe. Modify this lesson if there is not one larva per pupil.

You can pick enough milkweed for several days, and keep the stems in jars of water or plastic bags in the refrigerator.

• Monarch larvae
• 10+ oz. plastic cups (one for each larva)
• Milkweed (at least one large leaf per larva per day)
• Triple beam balances (or electronic scale, if you are lucky enough to have one)
• One Data Organizer: Hungry Caterpillars for each student, pair, or group (student handout page)
• Plastic wrap or petri dishes

1. Ask students if they have read The Very Hungry Caterpillar by Eric Carle. You may wish to read it to them at this time, and ask the following questions:

2. Ask your students:

• How could you measure the amount of milkweed your caterpillar eats during a day?
• During 24 hours?
• During a week?

3. List students’ ideas for measuring how much a larva eats on the board. If it is suggested, you could use the method described here. You may also opt to use one of the other methods students suggest, or allow groups to pursue different methods.
4. Divide the class into small groups. Assign roles. Ask the Getters to come up and get the larvae for their group, one piece of milkweed for each larva, and a Data Organizer: Hungry Caterpillars for each student.
5. Each student should trace the milkweed leaf on the grid of the Data Organizer: Hungry Caterpillars. Count the number of squares within that leaf shape. Discuss strategies for counting partial squares. Place the milkweed and larva in the empty, clean container. Cover with a petri dish or plastic wrap. Assure the students that there will be enough oxygen for the larvae to breathe for one day.
6. Students should estimate how much their larva will eat (in squares or as a percent of the whole leaf). (i.e. How many squares of leaf will your larva eat by ____ (time) tomorrow?) Have students describe their testing procedure (what they will do to measure how much the larva will eat). Record the surface area of the leaf tracing in squares. Students may draw illustrations of their procedure.  
7. Large larvae should get 2 leaves. Place the cups out of direct sunlight, or away from other heat sources. If the room is dry, add a damp piece of paper towel or filter paper. Be sure to replace it every couple of days to prevent mold.

Procedure: Part 2—Doing the experiment and analyzing data

1. Remind students what question they are trying to answer from the last lesson: How much food does one monarch larva eat in a given period of time? Have them look at their data sheets to see what predictions they made. Decide how you would like to have your students compare their predictions to their results.
2. Ask Getters to get the larvae for their table. Instruct students to get their log books and the Data Organizer: Hungry Caterpillars sheet.
3. Set the eaten leaf directly over its tracing on the Data Organizer: Hungry Caterpillars. Students should trace around the eaten portions of the milkweed leaf. If the leaf is wilted, this must be done with care and patience. When they are finished tracing, students need to count the number of squares that were eaten, using the same strategies they used in part 1. 
4. Have students compare their estimate with their actual square units of milkweed eaten. Then students can calculate the percentage of the total milkweed that the larva ate:
   
          (number squares eaten / total number of squares in the leaf) x 100 = % eaten
   
5. As a class, find the average amount of milkweed a monarch larva eats within the time frame you chose. You might average the number of squares or the percentages. Before doing this, list the data on the overhead and ask students to predict the average. Determine if this varies with larva size or other factors, such as whether they were molting. 
6. Assess student understanding by giving them a leaf tracing on graph paper, with an area outlined to represent the amount that a certain larva ate during a 24-hour period. Ask them to estimate the amount eaten, then count the actual amount eaten in square units. You might ask them to estimate percent eaten and calculate the percent eaten, if an understanding of percent is a desired outcome.
7. If desired, have students graph the results over several days as a class or in small groups. You can use averages, or make a separate graph for each larva.
8. Students often ask whether larvae eat at night. You may repeat this activity, measuring what was eaten during the day and night (from the time school ends to the next morning). Separately compare these amounts.
9. Modification: To make this lesson easier for young students, enlarge the graph paper on the student handout.

Worksheets

The following is an example of the worksheet necessary for this lesson. You may print it directly from the site. If you experience problems, please email us at webadmin@monarchlab.org

• Data Organizer:  Hungry Caterpillars
  

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