A leecher was a type of organism that fed by draining the minerals, pheromones, and stimulants including adrenaline from their prey's kidneys and adrenal gland. Higher quantities of these substances were produced if their prey was scared and a body devoid of these substances had an unusual lack of smell. Both the Ju'wes and Re'nar were types of leechers which could drain by touch.
After the war, Mac'atyde hunted and killed for sport, committing what were considered atrocities by the standards of other leechers. As Jack the Ripper, he brutally sliced and cut women to induce an intense fear response before they died. (COMIC: Ripper's Curse)