I'm not an expert, but i vaguely recall that spiders can go weeks between meals, as long as they have access to drinking water. No doubt someone with more knowledge than I on this subject (not difficult!) will be along in a minute, and Quizzy will give you a website.
A friend of my wife is scared of spiders and she believed that they slid down a thread at night to sip moisture from the corner of her mouth. So she Cellotaped her mouth up,priceless!
OK so not exactly an answer to the question but...
Aparently a spider crawls across your face an average of eight times per night whilst you're sleeping.
:-o