Wasps are champion predators of garden pests of all kinds, are they feeding on anything? They are carnivorous and not plant pests - until they get drunk on over-ripe autumnal fruit and go round looking for fights.
Good grief, don't kill 'em. They're scoffing greenfly or cabbage white larvae etc. Send them over here once they're done and they can have a go at the greenfly in my garden.