I'm not terribly worried by the vast majority of creatures, and I'll happily be around pets of many descriptions (including lizards/snakes etc.), but spiders are the one category I loathe. It seems to be purely as a result of some mis-wired instinct; I've never had any particularly bad experiences with spiders/insects/etc. but my brain just reacts really badly, even to quite small ones.
I remember a few holidays when I was young, deep in various bits of the UK countryside, where there were houses with certain rooms I couldn't go in because I felt some great big house spider was stalking me. (Why do spiders like the countryside so much? Surely the density and choice of creepy crawlies is much better in an urban environment?) And so it goes on.
My tactic of choice is to use a large vacuum cleaner, with the carpet brush head removed, on full power mode. Normally they don't reappear after that. I had a dedicated spider vacuum cleaner once, but it wasn't powerful enough. As a result of that experience, I also like to keep the hoover at arm's length...
Funnily enough, if I'm out in the wild camping out somewhere, rather than in a building, I'm a lot calmer. The spiders tend to get interested in something else quite quickly, and disappear never to be seen again.
I have seen some truly massive stuff in the UK, though. I remember some huge spider dangling at head height from the top of a lamppost (!!!), partially absorbed in some sort of goo which it was dealing with, on a residential road near a school in my area a few years ago. I did wonder why almost everyone was crossing over the road until I got a bit closer! It must have been at least the size of a lunchbox and clearly terrified a lot of people. Then there was the wall-clock-sized "thing" I found in a barn conversion in the Scottish Borders, and something similar in an old mill in Somerset. I can promise you that despite my abject fears of these creatures, I am not exaggerating these matters. I have a fairly keen eye for dimensions; I used to study various graphic design disciplines where I spent years accurately estimate things about this size.