University of Minnesota

Caterpillars Pupating and Emerging in Heat and Cold

Judy Falvey
McGuire Jr. High School
Lakeville, MN


The purpose of this experiment is to find out if heat and cold affects pupae emerging into monarchs.


The fifth instar caterpillars will go into pupae and emerge more quickly in the heat than in the cold. This will happen because monarchs are cold-blooded and so are the temperature-dependent pupae. Those in the warmer weather will go through the cycle more quickly than those in the cold. The caterpillars in the cold will either freeze to death, or they will take longer to go into the pupa and emerge because they will be using so much energy, just trying to stay warm

Background Information

Through our research we found that the pupae are temperature dependent and that the shortest life cycles are generally in areas that have long warm periods. We also found out that cold air will make these cold-blooded insects freeze to death. Monarchs are unable to travel in cold weather, and therefore lay their eggs and start their travel south soon enough so that they will not freeze. When the monarchs emerge in cold, they are biologically and behaviorally different than the monarchs that emerge in the spring and will not lay their eggs or mate until the following spring.


  • four caterpillars
  • refrigerator
  • heat pad
  • two shoe boxes
  • fresh milkweed
  • big box (the size of the inside of the refrigerator)
  • two thermometers
  • two aluminum sheets


During this experiment, the lights were always off and the boxes were the same size so that the results were only affected by temperature. The boxes were in the same spots and the test samples were checked at the same time each day so that the results would be accurate. The same caterpillars were used throughout the whole experiment. All of these things were done to get as accurate information as possible.


The dependent variable was the pupae being affected because they relied on the temperature to survive. The independent variable was the temperature because that stayed the same whether the pupae died or not.


  1. Find four shoe boxes.
  2. Write group name and box number on each to tell the boxes apart.
  3. Put one fourth instar caterpillar in each box.
  4. Put damp paper towel and two milkweed leaves in each box and change daily.
  5. Record size, activity, and how much eaten on the first day for each test sample. ( ex. Cold #1: 37 mm.; Color: normal; Didn't curl up when touched; Ate-. 1/10 of a leaf. Cold #2 ... )
  6. Put two shoe boxes in the refrigerator with a thermometer.
  7. Check and record the temperature and any observations of the larvae
  8. Place two heat pads on medium setting between two aluminum sheets and place in big box.
  9. Put the other thermometer and the other two shoe boxes inside the big box.
  10. Check and record the temperature and any observations of the larvae each day.
  11. Record how quickly each larva goes into a pupa and when each emerges, as well as any deaths.
  12. Record any significant observations about each pupa (color, size, temperature, etc.).


In this experiment I tested larvae pupating and emerging while being affected by heat or cold. Each test sample was in a separate container to get the most accurate results. I did this to see if the monarchs that go through their cycle in the late summer or early fall are different than the ones starting the cycle earlier on.

The larvae in the cold, as illustrated on my graph, were much slower in pupating and emerging, and the test sample number one didn't even pupate. Each day, the one of the larva seemed to shrink and become less and less alive. By the third day, it had stopped eating, and we were forced to bring it into room temperature to revive it. The cold must have been too drastic for it, because three days later it died. They warm larvae, as illustrated in graph two, had much more successful lives. Most pupated and emerged many days early, and they were very successful afterwards.

(Photo: Judy Falvey)
(Photo: Judy Falvey)

I felt that while doing this experiment, I had too many variables. This made it difficult to come to a general conclusion, and display my information. I don't think that this affected my information enough to further investigate it, though.

I could have changed the lighting to make it more real to life, but my data was so drastically different between the two tests that it probably wouldn't have made a difference. Overall, the results would be similar each time I tested it because there is proof that monarchs cannot handle cold. Next time I would just test larvae, or pupae, instead of so many groups.

I felt that testing larvae pupating and emerging while being affected by temperature was a good test to see if the monarchs going through the cycle in the spring would live longer than the ones in the late summer or early fall. I felt that my experiment was real to life, and as accurate as I could get it. I learned that pupae cannot live without heat.

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