Wasps on the wing

I have seen wasps catch hoverflies, pin them down, bite their wings off and then fly away with them. Why are they doing this and what are they doing with the bodies? ■  I first saw wasps doing this early one morning. I had been inspecting moths that were attracted to the light on my balcony. When a bright light confuses them, some moths settle down, thinking it is daytime.  This exposes them to predators at dawn because once their muscles have cooled at rest, they are unable to fly away immediately – they must first warm their muscles by vibrating their wings. However, if moths are threatened, they can make short hops of 30 centimetres or so. That morning, I watched a moth try to escape a wasp by hopping around the balcony until, alas, it was caught. The moth was larger than the wasp, so the wasp dissected its catch into chunks and made off with them, piece by piece. Since then, I have learned that it is not safe to open a mothcollecting box outdoors. Any  wasp in the vicinity will fly straight into the box and you are faced with trying to swat it away without damaging the specimens or being stung. We usually see wasps during late summer and autumn when they head for anything sugary.  By then the colonies have broken up and the insects are searching for food before the first frosts kill them. This behaviour gives the impression that wasps, like bees, feed entirely on sweet things. But wasps are predators. They sting their prey and feed it live to larvae in the nest. The larvae in turn provide sweet secretions that the adult wasp then consumes. A hoverfly makes an ideal meal. Once subdued it will be carried to the nest and popped into one of the egg chambers for the young  to feed on. Its wings have no food value – the wasp bites them off so they don’t catch the wind and destabilise its flight, and because they are an encumbrance in the nest. Wasps effectively control insect populations. Eradicating them would almost certainly have dire consequences of the kind China experienced around 1960 after Chairman Mao Zedong urged people to eradicate birds guilty  of eating grain. Insects took over where the birds left off. Terence Hollingworth Blagnac, France Readers should be aware that it is illegal to collect endangered species of moths in some countries – Ed