All spiders are predators and feed on a wide variety of insects and other soft-bodied invertebrate animals. Spiders attack and subdue their prey by biting with their fangs to inject poison. Spiders are beneficial in that they keep other insect populations down. All spiders spin silk and most construct a silken case to protect their eggs however not all spiders make a web. Every spider is poisonous but fear of all spiders is unwarranted because most spiders poison is too weak to harm humans. Only a few have bites that are dangerous to humans however the bite of these few species can cause serious medical problems and possible death under certain circumstances. The most dangerous spiders to humans in North America are the black widow, the brown recluse and the tarantula.
Adult female black widows are much more dangerous than males or juveniles. They are black in color with red triangular markings on her underside that often resemble an hourglass in shape. They avoid light and seek prey at night.
Brown recluse spiders are two to three centimeters in diameter and have a dark violin pattern on the front portion of their body. They readily enter human dwellings and hide during the daytime in baseboards, ceiling cracks, furniture and in piles of clothes. The bite of the recluse may either go unnoticed with no after effects or may be followed by a severe localized reaction characterized by scabbing, sloughing off of affected tissue and very slow healing.
Tarantula's are very large hairy spiders up to fifteen or more centimeters in diameter. They are generally nonaggressive and rarely bite; even if they do bite it's not considered to be dangerous and causes little lasting pain. Most of their danger is psychological as they are so menacing looking.