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← Insects are scared to death of fish

Alan4discussion's Avatar Jump to comment 28 by Alan4discussion

@OP - 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. "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," says Rowe.

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Comment 27 by DavidMcC

... One final point: there is no mention in the article of the flies even trying to fly away from the predator. This suggests to me that they were not distressed. This only leaves eustress as the cause of the shorter lifespan, unless there's something we're not being told about the insects' behaviour.

The point being missed, is that - The young nymphs develop under water, and the adults fly above it. - http://www.naturegrid.org.uk/biodiversity/invert/dragnfly.html, so the issue of nymphs flying away does not arise. They are aquatic and cannot fly. They only emerge in metamorphosis to the flying adult form ( with some dying in the process).

I think the points made @23 by Jessiperite are valid. In their immature aquatic stage the nymphs would be hard wired to flee and hide from large predators, so if kept in view of, or near predatory fish without the chance to flee and hide (under rocks), they would be stressed or distracted from feeding and growing normally.

They eat: other animals. Both dragonfly adults and nymphs are carnivorous.

The nymphs eat lesser water boatmen, pond snail eggs, water fleas, bloodworms and even newt larvae and small fish. Dragonfly nymphs, have a special hooked "mask" which can be shot forward to catch their prey.

As active predators themselves they would be evolved to identify prey and avoid predators which would threaten them. Size would be a major issue with fish! The nymphs have to hunt or ambush prey to feed.

Sat, 12 Nov 2011 23:23:28 UTC | #889725