Spiders and rain

I sit here by the window and I'm watching the rain come down in sheets. And there's a spider outside my window. He/She is sheltering in a little nook, which can't be much shelter. I'm a monster though. I look at his/her eight legs and they are very long and black and frightening to an arachnophobic like me. But what harm will he/she do me? Why don't I have the courage to open the window and let him/her in?
I don't and I'm almost helpless between my irrational and strong fear and my outrage that I would let anything stay out on a night like this.