HOUSEHOLD INSECTS 235 



solution ; having done so, the liquid is sucked up by a 

 powerful pump-like structure, situated just behind the 

 mouth, into the crop, which is really a food reservoir on 

 which the fly may draw when at rest, much as a ruminating 

 animal does when chewing the cud. Frequently the fly 

 regurgitates some of this food and deposits it on the 

 surface where it is resting, in the form of a light-coloured 

 vomit spot (fig. 59), easily distinguishable from the brown 

 excrement spot. Sometimes the regurgitated food is re- 

 absorbed instead of being deposited as a vomit spot. 



Known practically wherever mankind exists, the house 

 fly may be said to be truly cosmopolitan, its range ex- 

 tending even to the Arctic and Antarctic circles, though 

 its abundance and activity increases with a rise of temper- 

 ature. Apart from temperature, the most potent factor in 

 the abundance of these insects is the presence of garbage, 

 for " filth and flies are practically synonymous terms." 

 " As illustrating the abundance of flies in relation to the 

 breeding places, Major Faichne, in India, reared about four 

 thousand flies from one-sixth of a cubic foot of ground 

 from a latrine and as many as five hundred from a single 

 dropping of human excreta. Herms in California obtained 

 ten thousand two hundred and eighty-two larvae of the 

 house fly from fifteen pounds of samples taken from five 

 different parts of a manure pile after four days' exposure. 

 The whole manure pile weighed about a thousand pounds, 

 and on a conservative estimate it would contain over four 

 hundred and fifty-five thousand maggots. From one and 

 three-quarter pounds of manure collected at random two 

 thousand five hundred and sixty-one pupae of the house 

 fly were obtained." These data show that the house fly 

 is remarkably prolific, mainly on account of its rapid 

 development and the prevalence of suitable media in which 

 to oviposit. 



Heaps of stable manure form the most favoured breeding 

 places for these insects ; but if this medium be not available, 



