Spiders are beneficial predators that help control insect populations, and produce silk and medically useful venom. Because most spiders are beneficial and not harmful, most do not need to be controlled. Some people, however, have allergic responses and severe reactions to venomous spider bites.
Many species of spiders are common household pests in the United States. Certain common household spiders spin webs over lamps, in corners and in basements. This creates an unsightly situation but causes no real harm. Remember that every "cobweb" was made by a spider. Although all spiders use venom when they bite and kill their prey, the black widow and the brown recluse spiders are the only North American species consistently dangerous to humans. Even though there is generally little danger of complications from spider bites, you should advise all spider bite victims to take the spider specimen with them (if possible) when consulting their physician.
Under most conditions outdoors, spiders are considered beneficial because they feed on insects. However, they are undesirable to most homeowners when indoors, and the unsightly webbing spiders use to catch insect prey usually outweigh this beneficial behavior.
Many spiders are associated with moisture and, therefore, are found in basements, crawl spaces, and other damp parts of buildings. Others live in warm, dry places so are found in sub floor air-vents, in upper corners of rooms or in attics. Most species hide in cracks, darkened areas, or other retreats which they construct of silk.