In this article we will discuss about the economic importance of houseflies.
Apart from their annoying habits the houseflies are carriers of organisms which cause several diseases in man. Flies feed on garbage, manure, and faeces; they also visit them for laying eggs, they pick up disease germs and then come to feed on dining tables, kitchens, restaurants, and sweetshops.
They pick up disease germs on their bristly legs and sticky pulvilli, then they come and brush their legs into human food. They also take in disease organisms into their alimentary canal which they transfer to human food through their faeces, and through exuding saliva and fluids of alimentary canal onto human food.
Thus, houseflies are very dangerous and transmit organisms which cause human intestinal disorders, such as typhoid, paratyphoid, diarrhoea, bacillary and amoebic dysentery, and cholera.
Besides these dangerous diseases they also play a part in the transmission of tuberculosis and virus of poliomyelitis, and cause food poisoning. Houseflies also feed on discharges from eyes and wounds, thus, they have been known to cause ophthalmia in Egypt and Greece, and yaws in the tropics.
The larvae of housefly ingest eggs of a nematode Habronema, the infection is passed to the pupae and to the adult flies which transmit the parasite to horses, but often the housefly deposits the nematode larva into eyes of children and, thus, causes conjunctivitis.
Often the eggs of helminth parasites of man have been found in the alimentary canal or faeces of houseflies and they transmit two such parasites, the eggs of Hymenolepis (a tapeworm) are transferred from the faeces of one person to infect another. Secondly, the eggs of another tapeworm Echinococcus found in dogs are transferred to human beings where they develop to form huge and often fatal cysts.