A little while back I was talking about the extraordinary number of insect species just within the UK, and I said:
What I find staggering about these numbers is that it implies there are so many different evolutionary niches available for such apparently similar creatures. Even the 51 species of mayfly are slightly mind-boggling, but how can there possibly be 6900 different ways of successfully being a fly?
Well, there are 6900 separate answers to that question, but here’s just one (typical?) example. They’re found a new species of fly in Scotland. “The tiny black Christii fly measures just 2mm long and lives under the bark of dead aspen trees.” But not, presumably, living aspen trees. Or dead willow trees.
Although I guess that just begs the question “what is so specialised about their behaviour that they can only live in such a narrowly-defined habitat?”