The idea that spiders crawl into people's mouths when they sleep is a common urban myth. However, the biology of spiders and of sleeping humans makes this scenario very unlikely. Human are not prey for spiders, and beds do not provide an attractive environment for spiders. In fact, spiders are very sensitive to vibrations in their environments, and sleeping humans give off a number of vibrations from breathing, heartbeat, and random movements. These alone would be enough to scare off most spiders. For their part, humans are very sensitive to crawling sensations on the skin, especially so on the face. Therefore, the sensation of an 8-legged spider crawling on the face would instantly wake even a deep sleeper.