This is a family I had been keeping up my sleeve for a rainy day, or worse. In December when flies were thin on the ground and I just needed just one more family to reach Dipteran glory, when all the world was doubting me and there was not a fly to be seen, I would put on my coat and hat and scarf and gloves and walk down the lane through the puddles in my wellies and nonchalantly stop at a holly bush, and there I would be sure to find evidence of Phytomyza ilicis, a very common member of this family of leaf-miners.
So I was slightly wrong-footed by this tiny fly turning up as a result of my improved work rate and vigorous sweeping technique. There isn’t a lot to see even at high power, and even though my new microscope is turning up tomorrow (!), I don’t expect to get any further identifying this specimen down to one of the 407 British species – they are more easily identified from the host plant and shape of the mine than they are from the adult fly. There is a very good website devoted to the leaf mines produced in Britain by moths, beetles, wasps or one of eight different families of flies. They don’t even post a picture of the adult insect – it’s all about the mines.
And of course when you starting looking at leaf mines, there is a whole new world of detail to think about – which side of the leaf was the egg laid on, does the mine start near the midrib and does it cross the midrib, is it a wandering line or a blog, what pattern do the droppings make – and many more characteristics too subtle for my eye yet. Having tried quite hard to find micro-moth leaf mines last year, I can confirm that it is hard to walk at a socially-acceptable pace while examining every leaf for signs of damage – maybe I will save a more detailed study of leaf mines for when I am really old! Though planning ahead doesn’t always work out, does it.