These large (30 cm long) nematodes of mammals, including humans, can cause pathology due to their size alone. A large infection can physically obstruct the bowel, causing death. Ascaris eggs, with their thick external layers, are famed for their longevity and resistance to harsh environmental conditions. Reports of eggs remaining viable for many years after such treatments as being painted under abattoir floors, are common. One problem this longevity poses is to sewage treatment facilities, and much research has been done to develop treatment protocols that minimize numbers of viable eggs left in sludge.