Only two spiders that are native to the U.S. can do real harm when they bite a person: Black widows and brown recluses. Black widows tend to live in woodpiles, along fences or in outhouses in the South and West. Brown recluses tend to live in garages, attics or piles of rocks or firewood in the Midwest or South.
Both of these spiders tend to keep to themselves. They don’t bite unless they’re cornered. People sometimes invade their spaces without knowing it. That’s when they get bitten.