If you put a dragonfly next to one of its biggest predators, it's way less likely to live a long, healthy life... but not for the reason you think. Fish can quite literally scare dragonflies to death.
Researchers at the University of Toronto placed some dragonfly larvae in the same tank as some fish. However, the dragonflies were not in any actual danger — they were in cages that kept them isolated from their would-be predators, and there were even little hiding areas inside the cages in case the dragonflies couldn't stand the presence of the fish any longer.
The results were a pretty stark indicator of how stress affects all species, not just humans. The dragonflies were 2.5 times more likely to die when they were in the presence of the fish than those who were kept well away. And it gets worse from there — four times as many dragonfly larvae failed to reach adulthood when surrounded by predators, and they were 10% more likely to die while metamorphosizing when a fish was watching them.
About the only good news was that this stress didn't affect the body size of the dragonflies, which was somewhat unexpected — high stress levels have been shown to hamper development in other species. The researchers don't know for sure what specifically caused the dragonflies to die when surrounded by predators, but the stress might reduce the dragonfly immune response, cause them to use energy less effectively, or provoke a bunch of different minor negative responses that add up to a potentially lethal combination.