There are a few venomous spiders in this country but in Virginia the venomous spider you are most likely to encounter is the Black Widow. The female black widow is capable of inflicting a bite with enough venom to cause dicomfort but in most cases the bite is not fatal. The black widow spider is usually found in a dark and secluded area and they are not aggresive unless they are disturbed, most often by accident.
The black widow spider is shiny black with red markings on the underside of the abdomen. Sometimes the markings resemble an hourglass and sometimes they are just spots. In any event it is worthwile to be wary of spiders that resemble this description. To avoid an encounter with one of these spiders avoid reaching into areas where these spiders might build their nest such as dark corners in a basement or garage, boots or shoes that have been sitting on the porch or in the garage undisturbed etc. If you are bitten by one of these spiders you should seek medical attention.