The following answer has been selected and edited by New Scientist staff
I was once idly observing a wasp crawling round the edge of a water lily leaf in my pond when it paused to drink. There was a sudden flurry of activity when a frog leapt from its hiding place and swallowed the wasp.
The frog did not appear to suffer any ill effects, so I captured another wasp, tossed the hapless creature into the pond and waited. The frog was slow on the uptake, but there was another disturbance in the water and this time a goldfish snapped up the wasp. The fish, too, seemed undisturbed.
My curiosity now thoroughly aroused, I wondered whether the fish could be induced to consume further wasps. For the next hour or so I continued to hunt down luckless wasps and throw them into the pond. Some got away, some were eaten by the fish, and a few were swallowed by the frogs.
John Crofts, Nottingham, UK