People tend to assume that a variety of bumps and blemishes are the work of unidentified spiders who roam their homes when the lights go out and feast on their skin until the morning comes. That's a product of at least two separate myths: One about spiders being naturally aggressive and the other about them being nearby all the time.
Spider bites are actually far less common than many people think. Like most creatures, a spider's natural instinct when trouble arises is to run and hide. That includes hobo spiders, those eight-legged critters often found in homes. These poor guys suffer from limited vision and their movements can be misinterpreted as aggression. Even the brown recluse and black widows — two types of spiders whose bites actually can do some damage to humans — are unlikely to sink their teeth into you unless provoked [sources: DeNoon, Scott and Bundle].
The pros say that unless you catch a spider in the act of digging in, the marks on your skin were probably caused by something else [source: DeNoon].