VI 

 HOUSEHOLD INSECTS 



THE HOUSE FLY 



THERE is no insect better known to the world at large 

 than the common house fly, Musca domestica, though, 

 truth to tell, this omnipresent insect is often confused with 

 other house-frequenting flies and with the lesser house 

 fly, Fannia canicularis, in particular. The house fly 

 belongs to the Diptera family, that is to say, to the two- 

 winged flies, its hind wings being reduced to a pair of 

 stalked knob-like structures, known as balancers or 

 halteres. A few anatomical details will render the be- 

 haviour and habits of the fly more easy to understand. 

 On either side of the head are the compound eyes, wider 

 apart in the female than in the male, and each composed 

 of about four thousand small eyes ; on the top of the head 

 are three simple eyes, arranged in a triangle. The most 

 important organ, from the housewife's point of view, is 

 the proboscis, in reality a modified mouth, terminated by 

 a pair of soft lips, forming a heart-shaped structure, in the 

 middle of which is the aperture through which food is 

 sucked ; this fly is absolutely devoid of any structure 

 capable of piercing the skin, though it is often accused of 

 biting, owing to the fact that it closely resembles the 

 stable fly, which has a piercing mouth. From the nature 

 of its mouth organs, all food normally taken up by the fly 

 must perforce be in liquid form. When sugar is the diet, 

 the insect first of all pours upon it a quantity of saliva 

 from its salivary glands, thereby bringing its food into 



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