Blowflies are large flies of the family Calliphoridae. Although the larvae of blowflies usually feed on decaying meat, they sometimes infest open wounds, eating healthy tissue. They may live within the flesh of man and his domestic animals, forming tumours.
The most dangerous species are the screw worms, which attack both man and livestock, especially sheep and goats. They occur in tropical regions and the southern USA. Several species of blowfly attack, and will kill, livestock in Australia, where these is a $150 million-a-year blowfly strike problem in sheep. The Old World screw worm is widely distributed in the Pacific regions, Australia and Asia, occurring in enormous numbers, breeding in decaying vegetation, manure, human excrement and carcasses. It is a most important vector of dysentery, jaundice and anthrax.