Spiders can live in dirty hair.
I worked in a hospital (legal office) and there was a very elderly patient who had put her hair up in a bun years ago and had never washed it. (As the hair would grow, she'd just fasten it down with more bobby pins.) In the ER, a nurse was bitten by a spider that had crawled out of it. The hospital had to shave the patient's head for health & safety reasons and, because of legal reasons, save the hair mass in a sealed hazardous waste bag. I had to type up the report and saw the evidence with my own eyes. It was, hands down, the most disgusting thing I had seen there and did give me nightmares. In fact, our whole office was itching our heads for days. LOL (Sympathetic response of course...)
updated by @kerry-loco: 07/23/15 03:04:39AM