The two spiders in United States that are poisonous: Black widow (southern and western) prefer staying hidden in sheds, garages or piles of debris. The female's bite is most dangerous. The venom of these spiders is very potent.
Brown recluse (southern and mid western states) range in color from cream to very dark brown; have six eyes; are known to occasionally bite humans, injecting their poisonous venom into the blood stream.