No hunting required: simply by being exposed to their prey, predators can prove lethal to them.

Shannon McCauley and her colleagues at the University of Toronto in Canada exposed caged dragonfly larvae (Leucorrhinia intacta) to predators, either fish or another dragonfly species. Survival rates of larvae not exposed to predators were 2.5–4.3 times greater than those of larvae that were exposed.

Another experiment focused on larvae attempting to metamorphose into their adult stage — 11% of those that had been exposed to fish died in the process, compared with just 2% of those in a fish-free environment. The authors suggest that increased stress made the exposed dragonflies more vulnerable to other potentially lethal factors.

Ecology 92, 2043–2048 (2011)