The brown recluse is easily identified by the "fiddle" on its back. Their bite could require medical attention due to the necrotic venom.
The black widow is not aggressive toward humans but is still considered the most venomous spider in North America. They are easily identified by the red hour glass mark on the underside of their abdomen.
The wolf spiders bite could cause uncomfortable symptoms but they're not poisonous to humans. They are easily identified with a distinct Union Jack impression on their back.