240 INSECTS AND MAN 



sense of smell by which their food is discovered is situated 

 in the last segment of their antennae. The yellow dung 

 fly, Scatophaga stercoraria, spends most of its time in the 

 vicinity of cow dung ; nevertheless, at times it finds its way 

 into country houses. The female is yellowish brown with 

 a hairless body and the male is bright yellow and hairy. 



The green-bottle fly, Lucilia ccesar, is not very common in 

 houses, though decaying animal matter, especially fish, will 

 often tempt it indoors. In appearance it resembles a small 

 blow fly, except that it is of a metallic green colour. Many 

 other flies, among them the cheese fly, mentioned else- 

 where, are known to enter houses, and the list of these 

 occasional intruders is a lengthy one. Though it cannot be 

 said that all, or even the majority, of the flies we have 

 mentioned carry diseases, all, with the exception of the 

 window fly, are closely associated with excrement and 

 decaying animal or vegetable matter, so that their bodies 

 are, perforce, soiled with unpleasant, if not injurious, 

 substances, and accordingly they should be looked upon as 

 enemies of mankind. We may aptly conclude our brief 

 review of the house flies in the words of Dr Hewitt: 

 " Many inquirers have asked whether house flies do not 

 perform some good service, in accordance with the doctrine 

 that there is some good purpose bound up in the existence 

 of every creature. To such persons my reply is in the 

 affirmative. House flies certainly perform a valuable 

 service; they indicate the presence of filth, and are the 

 sanitarian's danger signals, his red lamps, in fact. House 

 flies are indications of the fact that insanitary conditions 

 are present, that the machinery requisite for an epidemic 

 of typhoid fever is in excellent working order, and that 

 more children are dying each year from intestinal disease 

 than should be the case. When these facts are realised, 

 the house fly will stand out in its true light as a potential 

 destroyer of human life." 



What can be done to abate this evil ? Much has been 



