This unidentified species belongs to the Blue-black spider wasps or Anoplius genus. Spider wasp is a common name for wasps that hunt spiders to feed their young. They are distinguished from other wasps by their extraordinarily long hind legs.
Protected deciduous forest (at Mason Neck National Wildlife Refuge).
This species carries an unidentifiable pray, probably a spider. On this picture, the legs with red strips belong to the pray.