Outdoor Life lists the top 10 most dangerous spiders as the Brazilian wandering spider, the black widow spider, the brown widow spider, the brown recluse spider, the six-eyed sand spider, the Chilean recluse spider, the northern funnel web spider, the Sydney funnel web spider, the wolf spider and the red-legged widow spider. Other spiders considered worthy of topping a "most dangerous and poisonous" list include the sac spider and the hobo spider. Due to the venomous nature of these spiders, which can potentially cause serious injury or death, it's important to avoid contact with them if possible, and if bitten seek immediate medical attention.
The venomous brown recluse spider is found in the United States and can be identified by the violin-shaped mark on its head. A bite from this spider can cause necrosis and tissue loss. The venom from the black widow spider can be fatal. A black widow is black with a red hourglass shape on its back.
The venom from a black house spider can cause dizziness, headaches, nausea, muscular pain and sweating. This spider has a brown- or black-velvet texture. The wolf spider is not aggressive, but its venom can cause very painful bites and is dangerous to humans. This spider is gray or brown in color and can be identified by the Union Jack pattern on its back.