M.G. Waldvogel, Extension Entomology Specialist. Spiders Spiders have a largely undeserved reputation as dangerous to the health and welfare of people and their pets. In truth, spiders are extremely beneficial because they prey on many pest insects. Not all spiders build webs to snare their prey.
Some species ambush their prey from tubular tunnels built in the ground or under rocks.
Other species, including those that most frequently live in homes and other buildings, simply build a loose collection of webbing in which they live. They may remain hidden for most of the day and feed primarily at night. Encounters between people and spiders are usually accidental and bites are a defensive response by the spider when its web or nest is disturbed. Young children, the elderly and hypersensitive individuals are most likely to react strongly to a bite. Biology Spiders are arachnids, not insects.