Pesky Fly

For the last couple of hours I have been sitting on my bed marking some essays (rather boring and tedious). And I have been bothered by a pesky fly that has been constantly been landing on me, trying to bite me. I think it must be quite an intelligent creature because it seemed to figure out that if it landed on my jumper or socks it could bite through - I know this because I felt its bites. However, when it was on my jeans I couldn't feel it.

A further thing that annoyed me is that it was seemingly indestructible. Whenever I tried to whack it with my hefty mark scheme, it seemed to know and flew away just in time. Spraying Impulse on it didn't seem to have any effect (I didn't have any fly spray handy - thought Impulse might choke it, but no...), and when I stood in the middle of the room, mark scheme poised, it went and hid until I had sat down again, at which point it tried to bite the back of my arm, presumably where I couldn't see it.

Why is it here anyway? Surely flies don't like cold weather - don't they all die, or migrate to warmer places? Or maybe it just doesn't like the cold weather outside and though it would come in and annoy me instead. I wonder how it got in - the window hasn't been open... it has probably got some crafty fly entrance and will be bringing all its friends once it tells them how it managed to outwit me. Grr!