Cellar spiders are not dangerous to humans, and their bites are usually not harmful. Although they may bite if they feel threatened, their mouths are too weak to break through human skin and inject venom. If a bite does occur, you may experience some mild pain, redness, and swelling at the site of the bite, but these symptoms should go away on their own within a few hours. Severe reactions are extremely rare and are not typically associated with cellar spider bites.