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Survival Rate of Monarch Caterpillars Raised in the Dark vs. in the Light

Robert Hermann and partners
St. Francis - St. James United School
St. Paul, MN

In our study we compared the survival rates of caterpillars raised in the dark and caterpillars raised in the light. We put the caterpillars into two groups. There were 48 caterpillars in the dark group and 40 caterpillars in the light group. We fed and raised them in the light or dark until they were butterflies. To figure out the percentage of survival in each group, we had to determine the number of caterpillars that pupated and emerged as butterflies. Of the 48 caterpillars raised in the dark, 25 emerged as butterflies. Of the 40 raised in the light, 34 emerged as butterflies. Our group did not think that being in the light or dark would make a difference in survival, but our study showed that it did. The final survival percentage for the light group was 85% and the final for the dark group was 52%.

(Photo: Robert Hermann)

The number of caterpillars that died in the dark was almost 4 times greater than those that died in the light. We thought that this was significant. The outcome of this study may have been influenced by some uncertainties including different temperatures for each group, different numbers of caterpillars in each cage, different amounts of food given to each cage, and pupae getting accidentally squashed and dropped. We do not know if this has affected the outcome significantly, but we think it still has made some difference.

This was a very educational project for the eighth grade. From our study, we learned that it is better to raise caterpillars in the light if a favorable survival rate is desired! We also found their migration routes to Mexico very interesting.

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