This story is also attributed to Robert the Bruce, hiding out in Scotland, back in the day. Just goes to show that spiders can be nice guys, if they're on your side.
Reminds of me about some of my soldiers, sharing a 20 man block. Should someone regularly annoy them (coming in late and drunk, snoring, farting etc), they would put the block tarantula on his face then shake his leg to wake him up. Didn't stop much of the behaviour, but everyone, almost everyone, had a good laugh and felt better about it. Gotta love a squaddie sense of humour.