Maggots of flies which eat the live flesh of sheep damage the fleeces, making shearing difficult and reducing their value, and can cause the death of the sheep themselves. The most amenable region for eggs to be laid and survive is the area under the tail of sheep, which is wet by urine and often has "dags" of congealed wool, faeces and blood. Muelsing is the term for the removal of skin and fat from the area around the anus and vagina of sheep. The cut is taken to the muscle and the scar that forms on healing is smooth and tough and resistant to being "fly-blown". The surgery is almost always done by shearers and farm workers without use of anaesthetic. Muelsing of lambs is usually accompanied by de-tailing and castration for males, either with a knife or the application of a ring so tight that it cuts off the blood supply and amputates the organ within some days.