The Black Widow Spider is one of the spider from the United States that is considered dangerous. There are only two other species, the Brown Recluse and the Hobo spider that are also considered dangerous. The Black widow spider is identified by the female being solid black in color with a red hour glass on the belly. She can have a red marking or hour glass on her back as well. Black Widow Spiders are not aggressive and rarley bite unless in self defense.
For my information click -> Black Widow Spider
Video of a Black Widow Spider
Black Widow Spiders are one of the easiest spiders to identify. They have a unique shape and the red hour glass is a positive identifier. If bitten by a Black Widow you should immediately go to the hospital. Quick care can really save a lot of pain and possibly prevent death.