While looking for animal classification cards I stumbled across a site which had ideas for detering spiders, including a spray which you can make yourself.
Being terrified of spiders I've placed the link in my favourites but thought I'd share the recipe here for anyone else who may not feel comfortable around incy wincys.
Mix 2 pints of water, 5 dops of any plant based essential oil, one ounce of neem oil and five tablespoons of soap. Spray in areas where spider appear to congregate - euuuurgh! It's not clear whether the soap is to be liquid soap or soap flake but I'm not certain it would matter as the flakes would dissolve anyway.
I'm not sure if it will work but I will certainly give it a try if I come across many this summer. If this fails apparently they hate the taste of Lemon Pledge!