If they love spiders enough to keep them as pets.
I hate spiders (more than I hate Kennedy and Clara from Doctor Who which tells you just how much I hate them), and I think it would be unfair to make a bloke choose between me and his beloved pets. However, I would be paranoid that a spider has escaped without him realising and stowed away in his coat pocket or something and then it'll be near me or escape into my home and lay eggs somewhere that hatch into little spiders. Basically if a guy has a pet spider, he is a no go.
What I want is a guy who doesn't mind spiders so he can get rid of any that come into my home (especially the really fast ones that are the Usain Bolts of the spider world and are bloody huge), but doesn't love them so he won't want to keep them as pets. Woe betide any bloke that throws a spider at me, I'd kick him to the kerb so hard, his feet won't even touch the ground.