There seem to be literally hundreds of these hoverfly thingies in my garden. They're like little flattened wasps and hover as if motionless, darting sporadically into the flowers. They do the same job as bees and wasps, i.e. scoff all the pollen, but I don't think I've ever heard of a 'hoverfly-nest'. Maybe they're nomadic and live in tiny little tents up in the trees? I'll have to investigate further...