16 March 2020 Evaluating Cardiac Reactions of Monarch Butterflies to Human Handling across Three Life Stages
Andrew K. Davis
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Humans have an especially close connection with the monarch butterfly, Danaus plexippus, and this connection often involves direct handling of larvae, pupae or adults. Monarchs are frequently handled in citizen science programs, education and outreach activities, classroom demonstrations, and when rearing larvae in captivity. A pertinent question is whether monarchs perceive this human handling in the same way as being attacked by a predator, i.e. does it trigger a physiological fight-or-flight reaction? Here, I investigated if brief periods of handling monarch larvae, pupae, or adults elevates their heart rate (a central component of the insect fight-or-flight response), using non-destructive methods: either microscopy or an electronic heart monitor designed for invertebrates. Results are presented from separate investigations on each life stage. Three minutes of gentle handling caused a significant elevation (20%) in heart rates of 30 fifth-instar larvae. Mild physical disturbance for 20 seconds to a collection of 57 pupae elicited brief bursts of heart contractions (∼88 beats/min), a rate which is three times higher than typical contraction periods at this stage. Adult monarchs captured during fall migration (n=72) showed minor heart rate elevations (6%) after 3 minutes of gentle handling for tagging purposes. The differences in reactions across life stages found here is helpful for elucidating the relative sensitivity of each stage to handling. More importantly, these results elucidate the unseen physiological impact of direct human contact on developing monarchs (larvae and pupae); elevation in heart rate is an integral part of the fight-or-flight reaction in animals and a universal sign that an animal perceives an imminent threat. In this sense then, developing monarchs appear to perceive human handling as a threat, which may alter our (human) perception of this practice.

Andrew K. Davis "Evaluating Cardiac Reactions of Monarch Butterflies to Human Handling across Three Life Stages," The Journal of the Lepidopterists' Society 74(1), 43-50, (16 March 2020). https://doi.org/10.18473/lepi.74i1.a5
Received: 21 August 2019; Accepted: 17 October 2019; Published: 16 March 2020

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Danaus plexippus
heart rate
Monarch butterfly
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