30 Guide lo Insects and Ticks 



of the insect shows tliat it has a straight piercing prohoscis 

 projecting forwards from the head. 



The common house-fly is incapable of biting ; its proboscis is 

 large and soft, and is situated on the under side of the head, and 

 contains numerous minute tubes through which fluid nutriment is 

 sucked. A fly cannot take in solid food ; if the food is dry, as for 

 instance a piece of sugar, the fly moistens it by ejecting salivary 

 fluid or by regurgitating the fluid contents of its storage-stomach 

 or crop. It is in this way, among others, that the fly infects food 

 with disease organisms, for flies are indiscriminate in their habits, 

 and the previous meal of the fly in question may have been made 

 upon the excrement of a person sufl'ering from typhoid, or of an 

 infant ill with summer diarrhoea. The mere walking of a fly upon 

 food may infect it with microbes, for the feet are hairy, and readily 

 carry minute droplets of substance that the fly has recently been 

 visiting. 



At one end of the case is shown a representation of a tray of 

 food such as might serve for a light lunch — a plate of ham, a roll, 

 a few plums and a jug of milk — looking repellent by reason of the 

 house-flies that swarm upon it. At the other end of the case is a 

 representation of a heap of kitchen refuse which, by being allowed 

 to accumulate for some time in the dustbin, forms a suitable 

 breeding-ground for house-flies ; for flies, although an indoor 

 pest, do not breed indoors. In this exhibit are shown the 

 four chief phases in the life-history — eggs, larvae or maggots, 

 resting pupae in their brown coats, and adult flies. In the heap 

 of rubbish can be recognised cinders, feathers, egg-shells, fish- 

 bones, mouldy bread, vegetable refuse and tea leaves, the last two 

 being particularly harmful because, by keeping the whole mass 

 damp and in a state of fermentation, flies are attracted to lay their 

 eggs in it, their instinct prompting them to deposit the eggs where 

 the maggots, on hatching out, will find themselves in surroundings 

 most suitable for their development. Flies breed also largely in 

 heaps of stable manure, and any decaying and fermenting vege- 

 table refuse in the fields. 



Just as the mosquitoes that carry malaria and yellow fever can 

 be kept in check liy attacking their breeding haunts, by preventing 

 accumulations of rain-water, by draining marshes and by spraying 

 with paraffin oil tracts of stagnant water, so as to prevent the 

 development of eggs and larvae that would grow into mosquitoes, 



