Melena is a term that describes a particular appearance of blood in stools. This term describes stools that are black, tarry and often foul-smelling because of the presence of blood from the upper gastrointestinal tract.elena may be caused by hemorrhoids. Eating blueberries may cause the appearance of red stools. Eating tomatoes may cause the appearance of bloody stools. Eating beets may cause the appearance of bloody stools.