I didn't actually know this myself until recently but spiders in the UK are actually capable of biting and drawing blood. I only ever thought it was the tropical ones that were capable of that, so I have a newfound respect for them! Anyroad, Bill Odie(?) says that it's not that spiders are getting bigger, it's just that the weather is getting warmer, there's thus more food, and so more of them are growing to maximum size. At least it's not centipedes that appear to be getting larger - that would be bad.