Flies

Everyone loves to hate them, but did you know that if it weren't for flies (or, more accurately, their larvae) we would be swimming in a sea of rotten vegetation and dead bodies six metres deep within a year?

Fly larvae eat enormous quantities of, well, how do I put this? crap. Without them, quite apart from all the hungry spiders and bored cats, life as we know it would be impossible because there would just be crap EVERYWHERE.