A poisonous snake of the Southern United States. The
   water moccasin (Ancistrodon piscivorus) is usually found in or near
   water. Above, it is olive brown, barred with black; beneath, it is
   brownish yellow, mottled with darker. The upland moccasin is
   Ancistrodon atrofuscus. They resemble rattlesnakes, but are without
   rattles.