The Most Dangerous Spiders in the U.S.

To their prey, all species of spider are deadly, since they all have some form of venom. In the U.S., though, most spider species pose little threat to humans unless a person has an allergy. A few of the country's species, however, can cause severe pain, illness and even death, especially if bites aren't treated.

  1. Brown Recluse

    • Found mainly in the central Midwestern states, the brown recluse is a relatively small brown spider with few distinctive features, meaning other brown spiders can be mistaken for it. A true brown recluse has a dark, violin-shaped marking on its back. It bites only in defense, and the severity of such a bite depends on how much venom is injected--some bites have little effect, but others can cause tissue death to the area around the bite. Untreated bad reactions can lead to severe scarring.

    Black Widow

    • The black widow is a much-feared spider, with a venom several times stronger than a rattlesnake's. The U.S. is home to several species of black widow, including the northern, southern and eastern varieties. Black widows are small spiders with large, round, black abdomens on which a red hourglass shape is evident. The spiders tend to try to avoid humans and will bite only in self-defense. Only a small amount of venom is injected, so bites are rarely fatal, but the venom is neurotoxic and can cause breathing problems, muscle pain and paralysis.

    Hobo Spider

    • The hobo spider, also known as the aggressive house spider, originated in Europe. In the U.S. it's found mainly in Washington, Idaho and Oregon in and around human dwellings. The spider's plain-brown coloring means it can be mistaken for the brown recluse or other, harmless species. It's considered an aggressive species that commonly bites in self-defense. It has a necrotic venom that can cause flesh to die, and some resulting wounds can take a long time to heal, leaving bad scarring.

    Black House Spider

    • The black house spider, often called the window spider, is a common U.S. species. It has thick legs and a large, hairy abdomen, and forms webs that have a tunnellike shape, often in window sills. It's not considered a deadly species, but bites from this spider can cause some serious adverse effects in some individuals, including muscular pain, nausea, vomiting and trouble breathing. This species bites only if threatened.