How do you get rid of spiders in a screen porch?

I'm cleaning for a lady, and she has a small screened porch. The problem is that it is infested with spiders!!!!!!!!!! Can you tell I hate them? lol Anyways I'm looking for a good solution or product I can have her buy to get rid of them and keep them out. Also she has a cat that enjoys being out there, so something that won't harm the cat would be great! Please help me!!!!!!!!!!!!!!!!!!!!!!!