Terrified Dragonfly Larvae Die of Stress From Mere Presence of Predator in Study

Posted on October 27, 2011

University of Toronto biologists conducted a study that found the mere presence of a predator causes enough stress to kill a dragonfly, even when the predator cannot actually get at its prey to eat it.

Shannon McCauley, a post-doctoral fellow, and EEB professors Marie-Jos�e Fortin and Rowe raised juvenile dragonfly larvae (Leucorrhinia intacta) in aquariums or tanks along with their predators. The two groups were separated so that while the dragonflies could see and smell their predators, the predators could not actually eat them.

Larvae exposed to predatory fish or aquatic insects had survival rates 2.5 to 4.3 times less than those not exposed. Rowe says, "What we found was unexpected - more of the dragonflies died when predators shared their habitat."

In a second experiment, 11 per cent of larvae exposed to fish died as they attempted to metamorphose into their adult stage, compared to only two per cent of those growing in a fish-free environment.

Rowe says, "We allowed the juvenile dragonflies to go through metamorphosis to become adult dragonflies, and found those that had grown up around predators were more likely to fail to complete metamorphosis successfully, more often dying in the process."

"The deadly effects of 'nonlethal' predators" report was published in Ecology and highlighted in Nature this week.

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