This sturdy-looking hoverfly lays its eggs near the a wasps nest, where its larvae enter the nest ultimately eating a wasp larva before re-emerging as an adult. It looks a bit hornet like. This one was on a wall where we have a few mason bees and wasps, but it is a male (eyes join on the forehead) so probably was getting some sun rather than being on the look-out for somewhere to lay its eggs.