Young monarch butterflies can get stressed out by people handling them, according to a study. This is especially so for the early stages of the larva (caterpillar) and the pupa (chrysalis) of the butterfly life cycle. Researchers at the University of Georgia published this finding in March 16, 2020 edition of The Journal of the Lepidopterists’ Society.
Handling butterflies is common in research and education, and the butterflies are subject to human contact at all life stages — larval, pupal and adult. Just like vertebrates, insects can get stressed out too in the same ways.
How Would You Feel?
Andy Davis, the author of the study, made an analogy with people handling butterflies.
“People handle monarchs for all of these activities, but if you imagine yourself in their place, what would it be like for us if a 50-foot-tall robot picked us up and passed us around? From the monarch’s perspective, maybe for them this is akin to being attacked by a predator,” he said.
Measuring Increased Heart Rate
Increased stress is related to elevated heart beats in insects. To look at stress levels from handling, Davis measured the heart rates of caterpillars, chrysalises and butterflies before and after short periods of gentle handling in his experiment.
For caterpillars, he counted the heart beats under a microscope before they were handled and after handling for three minutes. For adult monarch butterflies, he similarly measured their heartbeats under a microscope 30 seconds after they were caught, and after they were simulated being tagged, such as what they would experience in a scientific experiment.
The chrysalises were more complicated to measure since their heart beats can’t be observed under a microscope, and their hearts tend to beat in short intervals. Instead, he used an electronic device that could remotely detect heart movement inside the chrysalis and provide a readout to his computer. He disturbed the chrysalises for 20 seconds to get their hearts beating, and then measured the heart beats for another 60 seconds.
Caterpillars and Chrysalises Get Stressed Out
The results showed that caterpillars experienced at 20 percent increase in heart rate over the resting rate after they were disturbed. The chrysalises showed almost three times higher heart rate than the typical active beating rate for pupae after they were disturbed.
Adult Monarch Butterflies Not Stressed Out
However, the adult monarchs showed no significant change after handling. This meant that the experiment could not capture their stress reactions, or they had no stress reaction from being handled. Davis suspects it’s the latter.
“It kind of makes sense that adult monarchs would be fairly stress-tolerant. The migration itself is fraught with dangers and perils along the way, and for a monarch to be able to accomplish that, it has to be able to deal with a wide variety of natural stressors,” he said.
Insects Get Stressed Out Too
Butterflies will continue to be handled by people for research and educational purposes. However, this study shows that people should know that at least at the caterpillar and chrysalis stage, these insects do get stressed out from being handled.