Wasps like to eat other insects. One morning I watched a moth get eaten by a wasp. The moth had been attracted to the lights near our back door, it must have settled there and this then exposed it to predators at dawn, because once thier muscles have cooled at rest, they are unable to fly away immediately; they must first warm their muscles by vibrating their wings. However, if they are threatened they have the ability to hop 30cm or so.
This particular morning a moth was hoping around trying to escape the attention of a wasp. The wasp being bigger, overcame the moth and disected its catch into chunks and flew away with them. Wasps are predators, they sting their prey and feed it live to larvae in the nest. The larvae then in turn produce sweet secretions that the adult wasp then consumes. The same goes for hoverflys, once subdued they are carried to the nest and popped into one of the egg chambers for the young to feed on.
The wings have no nutritional value, so they are bitten off early in the contest, also because they may catch the wind and destabilise its flight, and because they are an encumberance in the nest.
Our wasps are good as they help to control our insect populations, without the wasps there would be a lot more insects.