Unwelcome Hitchhiker

I was driving home when something inside the car caught my eye.

I've absolutely no idea where this insect came from or what it is (can anyone tell me?). I really don't like it when even the tiniest of flies get trapped in the car; I find them really distracting. And this one was not tiny. I pulled over very quickly and opened the window to chase it out, but then plucked up the courage to photograph it, as I'm struggling to find something to illustrate the weekly blip challenge of 'horny' and thought that this might just fit the bill. OK, I know they are antennae, not horns, but use your imagination...