628 Journal of Agriculture, Victoria. [10 Oct., 1917. 



THE HOUSE FLY. 



By J. W. McKenzie, Dairy Supervisor. 



It is to be feared and regretted that tlie common house fly (Mv^ca 

 doniestica) is not generally recognised as being a most active dissemi- 

 nator of filth and disease. A study of its life history and habits leaves 

 one amazed at the toleration and indiifcrence displayed towards a pest 

 as repulsive as it is dangerous. It is incumbent upon dairy supervisors 

 and Board of Health inspectors to give effect to provisions of law, com- 

 pelling manufacturers of and traders in foodstuffs to protect their wares 

 from contamination by flies, and their efforts have had a salutary effect 

 upon tradesmen found lax in their methods. Much good Vork by super- 

 visors and inspectors is, however, nullified through apathy, carelessness, 

 and ignorance on the part of housekeepers given to methods favorable 

 to pollution of food by flies in the home. 



Towards the beginning of summer, the remnants of the preceding 

 year's countless army of flies will crawl drowsily from the chinks and 

 crevices which have afforded them shelter during the winter. Their 

 ranks are reinforced by the generation whose members about the same 

 time emerge from their pupa cases, and with all the energy of youth 

 are ready to sally forth upon their disease-spreading career. After 

 having gorged themselves upon any food left accessible to their greed, 

 the production of a further generation is proceeded with. The female 

 lays about 120 dull, chalky-white, elongated eggs, about l-25th to l-20th 

 of an inch in length at a time. This performance is repeated three or 

 four times in a season. Upon pieces of meat, house refuse, or in accumu- 

 lations of manure, the eggs are deposited, and within a few hours white 

 footless maggots (larvae) are hatched, and these at once voraciously 

 attack the organic matter close at hand. Although the larvse finds 

 other bacteria thriving and multiplying in the same repulsive surround- 

 ings, there is no pitched battle between them. On the contrary, the 

 larvEe finds a useful ally in the bacteria, as it liquifies that portion too 

 solid for the tender jaws of the young maggots; they, in return for this 

 service, expose fresh surfaces of food for the bacteria. In favorable 

 circumstances the maggot attains its full size (from ^ to 2-5th of an 

 inch) in five days, and, having reached maturity, ceases to eat, and 

 changes into a chrysalis or pupa, a dark-red object, about ^ inch long, 

 enclosed in a hard tough case. The pupa lies in the food substance or 

 on the ground for a period of from five to fourteen days, and during this 

 time changes into a fly. At first, flabby and soft, though fully grown, 

 when it leaves the pupa case, its wings are only partially developed; 

 but in a short space of tijue its skin hardens and the wings expand. 

 The fly is provided with a proboscis or trunk-like attachment to the 

 head. This truuk terminates in a tip, which, when the insect is feeding, 

 expands into an oval disc. This disc is connected with numerous 

 channels converging towards the gullet. These channels pass into the- 

 thorax. A pumping organ near the proboscis enables the fly to suck 

 up liquid sustenance. The gullet is divided in the thorax, and both 

 branches pass into the hinder part of the abdomen. A large sac — the 

 crop — is connected with one branch, while the other passes into the 



