Animated coloured scanning electron micrograph (SEM) of House fly (Musca domestica). The house fly, Musca domestica, is a well-known cosmopolitan pest of both homes and farms This species is always found in association with humans or the activities of humans. House flies are a nuisance and also transport disease-causing organisms. The adults feed on a variety of liquid or semi-liquid substances beside solid materials which have been softened by saliva. They carry pathogens on their bodies and in their faeces and can contaminate foodstuffs and contribute to the transfer of food-borne illnesses. For these reasons they are considered pests. They have been used in the laboratory in research into ageing and sex determination.