Necrosis (tissue death) from animal venoms, such as the tentacles of jellyfish is usually self-limiting in area and duration and not gangrenous. The body can replace the damage. In certain rare cases of necrosis from spider bites the tissue death is extensive and irreversible. It may start with surface blistering, or with darkening below, but proceed into deeper layers. It can be rapid and agonising, accompanied by drastic attacks of vomiting and diarrhoea. Or, it may be gradual with very little pain. One case had a fast onset and a slow, relentless continuation. The damage can only be repaired by involves skin grafts; where gangrene sets in amputations are necessary. The two spider suspects are the White Tail spider and the Wolf spider. A bacterium Myobacterium ulcerans is beleived to be carried in their venom. This microscopic organism does the damage, causing a spreading, infected ulcerous sore.