There are more than 35,000 known spider species in the world, with only about a tenth (3,500) of those appearing in the U.S. and often only one tenth (350) of those in any single region. In general, spiders are beneficial creatures, preying and feeding on flies, crickets, mites, and other household and yard pests. Most are completely harmless to humans.
Most spiders bite only in defense, when handled or disturbed. When a bite does occur, few are actually of any danger to humans, primarily because, even when venomous, the spider's small size and amount of injected venom generally have little effect on the much larger human. There are, however, some exceptions to this and general guidelines for symptoms and treatment.
Some of the more common, and commonly feared, spiders in the U.S. include:
- Black Widow – The female's body is about 1/2 long with the well-known hourglass shape, which can range in color from red to yellow. Considered to be the most venomous spider in the U.S., the bite of the black widow can cause severe pain and flu-like symptoms, but severe long-term reaction or death are very rare. Indoor webs are often very low, near the floor, in hidden areas; they can be up to a foot in diameter. Like many spiders it can be beneficial, as it feeds on live insects, other spiders and arthropods.
Read more about black widow spiders.
- Brown Recluse – Both the male and female brown recluse spiders are best identified by the violin marking on its 3/8-inch-long body. Though not usually aggressive, this spider may bite if disturbed or handled. While many people have little reaction to the bite of most of these spiders, others may experience a deep wound. A large amount of venom injected in sensitive people can result in killing and scarring of the tissue around the bite.
Read more about brown recluse spiders.
- Tarantula – The heaviest of spiders, the tarantula is easily identified by its large body size most commonly up to about 1 1/2 inch in the U.S., and hairy body and legs.
Although many fear the "deadly" bite of the tarantula, those found in the U.S. are not poisonous, nor even considered to be dangerous. While these spiders can bite, and it can hurt or even cause allergic reaction in sensitive people, the bite of a tarantula is no more to be feared than the sting of a bee.
Read more about tarantulas.
- Wolf Spider – Sometimes thought to be tarantulas, wolf spiders can be up to 1 3/8 inches in body length. Although wolf spiders are also hairy, their legs are long and spiny, unlike the hairy shorter legs of the tarantula. Though they are not aggressive, their size often scares people; but they will generally only bite if handled or disturbed. As their name indicates, wolf spiders are hunters and usually come indoors only in search of food.
Read more about wolf spiders.
- Common House Spider – At 1/3 inch long and grey to brown, the common house spider has dark stripes near the tip of its abdomen.
A member of the cobweb spider family Theridiidae, this spider and its webs are most likely to be seen in a damp basement, crawlspace or outbuilding. This spider needs plenty of prey and will abandon and reconstruct webs until finds the best capture area.
- Daddy Longlegs – Although not actually spiders, these arachnids are commonly found around the home. More correctly called harvestmen, this "bug" is harmless to humans and is, in fact, a beneficial "pest" as it feeds on live invertebrate prey such as beetles, flies, mites and even spiders. Read more about Harvestmen spiders.