74 THE HABITS AND BIONOMICS OF THE HOUSE-FLY 



extremity of Porter's Island was used as a garbage dump (C) until 

 June 1911, this being about 170 yards from the isolation tents and 

 hospital. Between the end of Water Street and Rideau River gar- 

 bage was being dumped (A), a large proportion of which consisted 

 of stable refuse (horse manure). At this place, which is about 530 

 yards from the hospital, flies were found breeding in considerable 

 numbers. At the foot of St Andrews Street, adjoining the river and 

 about 270 yards from the hospital, about 100 tons of horse manure 

 and compost had been dumped (B). There were in addition 

 numerous breeding places apart from an unusually large number 

 of unprotected heaps of horse manure in stable yards. Conse- 

 quently flies were extremely abundant on the island and through- 

 out the district. The presence of countless numbers of flies in the 

 district which were bred in these natural breeding places made the 

 recovery of 172 marked flies out of a total of 13,500 which were 

 liberated all the more remarkable. 



The results of these experiments indicate in a significant 

 manner the distances which, under city conditions, flies are able to 

 travel from their breeding places or from a source of infection \ 



Feeding Habits and the Influence of Food. 



The fact that the fly ingests micro-organisms on account of its 

 indiscriminate feeding habits and that bacteria remain in a viable 

 condition in the alimentary canal for a gi'eater length of time and 

 in larger numbers than externally renders a consideration of the 



' Since the above was written the results of further experiments on the range of 

 flight of house-flies have been published. 



Nuttall, Merriman and Hindle (1913) carried out a series of experiments in 

 Cambridge. They liberated upwards of 2.5,000 flies marked with coloured chalk 

 dust. The maximum flight in thickly-housed localities of the flies recovered was 

 about a quarter of a mile ; in one case a single fly was recovered at a distance of 

 770 yards, part of which distance was across fen-land. It is considered by the 

 authors that the chief factors favouring the dispersal are fine weather and warm 

 temperature. The nature of the locality is a considerable factor. 



Zetek (in a paper presented at the meeting of the Ent. Soc. of America, Atlanta, 

 Ga., Dec. 31st, 1918) describes experiments carried out in the Panama Canal Zone. 

 He showed that marked flies had flown from the breeding place (cow manure) to 

 dwelling places situated 2500 feet away and at a lower level of 150 feet. 



Hodge (1913) in explanation of the discovery of flies 1^, 5 and 6 miles respec- 

 tively out from the shore of Lake Erie (U.S.A.) suggests that they were carried by 

 the wind. 



