FEEDING OF FLIES OX FAECES 311 



The feeding habits of th<' li<>use-fly ha\i" .ilready been described 

 in an earlier chapter, but on account of its particular interest in 

 connection with the possibility of the dissemination of parasitic 

 worms by flics fi-('((nfiiting excrement, I have reserved a (piDtation 

 of Nicoll's own observations on this point for the present section ; 

 these observations have been repeatedly confirincrl by myself and 

 doubtlessly by other investigators. He says : " It is a matter of 

 common observation that fresh and moist faeces attract flies much 

 more readily than old dried faeces. Flies feed on warm fresh 

 faeces with considerable avidity, and they will do so even although 

 they have been previously feeding on other material. To flies 

 which have not fed for some time the presence of fresh human 

 faeces acts as an immediate source of attraction, and in some of 

 my experiments the eagerness with which they attacked it was 

 most striking. When the portion of faeces was so small that the 

 flies could not find standing room upon it or around it, thev 

 struggled together and pushed each other aside, and more than 

 once I have seen them so closely packed together that each fly 

 could find room only for the tip of its proboscis, the flies on the 

 top practically standing on their heads, supported by the bodies of 

 those around. Their behaviour towards older faeces, however, is 

 very different. When the material has become cold it does not 

 attract flies nearly so readily. So long as it remains moist it con- 

 tinues to attract and does so quite as much as moist bread, 

 although very much less so than moist sugar. When it has become 

 dry it possesses little or no attraction, but this is increased when 

 it is moistened again. It is evident, therefore, that the presence 

 of moisture plays an important part in a fly's attitude towards 

 faeces as an article of food. 



" When the alternatives of fresh faeces, sugar and bread were 

 offered, the flies did not confine their attention to any one of these 

 articles but made repeated excursions from one to the other." 



He proceeds to describe some interesting observations in regard 

 to flies feeding on segments of tape-worms. Such tape-worm seg- 

 ments may be deposited together with the faeces or independently 

 and in the case of some species of parasitic worms the eggs are 

 conveyed to the exterior in the detached segments instead of 

 being shed singly into the gut. It was found that such detached 



