THE TYPHOID FLY, OR HOUSE FLY. 31 



Strange as it may seem, an exhaustive study of the conditions 

 which produce house flies in numbers has never been made. The 

 life history of the insect in general was, down to 1873, mentioned in 

 onl}' three European works and few exact facts were given. In 1873 

 Dr. A. S. Packard, then of Salem, Mass., studied the transformations 

 of the insect and gave descriptions of all stages, showing that the 

 growth of a generation from the egg; state to the adult occupies from 

 10 to 11 days. 



In 1895 the writer traced the life history in question, indicating 

 that 120 eggs are laid by a single female, and that in Washington, 

 in midsummer, a generation is produced every 10 days. Although 

 numerous substances were experimented with, he was able to breed 

 the fly only in horse manure. Later investigations indicated that the 

 fly will breed in human excrement and in other fermenting vegetable 

 and animal material, but that the vast majority of the flies that 

 infest dwelling houses, both in cities and on farms, come from horse 

 manure. 



In 1907 careful investigations carried on in the city of Liverpool 

 by Robert Newstead, lecturer in economic entomology and para- 

 sitology in the School of Tropical Medicine of the University of 

 Liverpool, indicated that the chief breeding places of the house fly 

 in that city should be classified under the following heads : 



(1) Middensteads (places where dung is stored) containing horse 

 manure only. 



(2) Middensteads containing spent hops. 



(3) Ash pits containing fermenting materials. 



He found that the dung heaps of stables containing horse manure 

 only were the chief breeding places. Where horse and cow manures 

 were mixed the flies bred less numerously, and in barnyards where 

 fowls were kept and allowed freedom relatively few of the house 

 flies were found. Only one midden containing warm spent hops was 

 inspected, and this was found to be as badly infested as any of the 

 stable middens. A great deal of time was given to the inspection of 

 ash i^its, and it was found that wherever fermentation had taken 

 place and artificial heat had been thus produced, such places were 

 infested with house-fly larvae and pupae, often to the same alarming 

 extent as in stable manure. Such ash pits as these almost invariably 

 contained large quantities of old bedding or straw and paper, paper 

 mixed with human excreta, or old rags, manure from rabbit hutches, 

 etc., or a mixture of all these. About 25 per cent of the ash pits 

 examined were thus infested, and house flies were found breeding 

 in smaller numbers in ash pits in which no heat had been engendered 

 by fermentation. The house fly was also found breeding by Mr. 

 Newstead in certain temporary breeding j^laces, such as collections 



