Blowfly strike (myiasis) is an important cause of sheep loss in the United Kingdom . Surveys of organic farming have highlight this as a health problem . Blowfly strike is caused by the invasion of living tissue by the larvae of dipteran flies. Several species of fly commonly parasitise sheep in the United Kingdom . These can be divided into primary and secondary flies.On average, 70-95% of blowfly larvae die overwinter although the action of biotic mortality factors, such as entomopathogenic nematodes and fungi are likely to be the primary cause mortality.