The answer to 'what causes spider' is that spiders are found in most homes due to their natural habitat and need for shelter. Spiders are attracted to homes because they provide a warm, dry environment with plenty of insects and other small prey for them to feed on. Common causes of spiders in homes include cracks and crevices in the walls, gaps around windows and doors, and cluttered or undisturbed areas like attics, basements, and garages.
Spiders are generally not aggressive towards humans and only bite if they feel threatened. While some spider bites can be painful or cause mild reactions, the vast majority of spiders found in homes are not venomous and pose little risk to people or pets. Keeping homes clean, sealing up entry points, and removing clutter can help discourage spiders from taking up residence.