94 ECONOMIC ZOOLOGY 



habits of the house-fly are studied. Nearly anyone knows that the 

 unpleasant maggots seen in decaying flesh are the larvae of flies, hatched 

 from the eggs laid in this flesh by the adult females in order that these 

 larvae may have food to eat while they are developing into the pupa or 

 chrysalis stage. These maggots may or may not be the larvae of house- 

 flies, probably they are mostly those of other species; but anyone may 

 see the whole process by watching a piece of stale meat some summer's 

 day. Usually one will not have to wait very long until a fly will light 

 upon the meat and will proceed to deposit her elongated, white eggs, 

 possibly at the rate of four or five per minute until a hundred or more 

 have been laid, Fig. 73. If the meat be kept moist and warm the next 

 day will probably see it swarming with tiny white maggots; these larvae, 

 in a few days, will grow to full size, will surround themselves with little 

 cases and become pupae. If the meat be in a covered vessel the flies 

 that emerge in a week or more, from these chrysalises, will be caught 

 and they will in turn, lay a new lot of eggs, though it may be a couple of 

 weeks after hatching before the flies become sexually mature and are 

 able to lay eggs. Since each fly may lay one hundred or more eggs in 

 each of five or six lots per year, and since the whole life cycle, from adult 

 to the next generation of adults, may take place in three or four weeks, it 

 will be seen that by the end of the summer the descendents of the first 

 few flies are to be numbered by millions; hence the importance of " swat- 

 ting" the first flies as they emerge from their hibernation quarters. 

 The life history of the house-fly is about as outlined above, except that 

 its favorite breeding place seems to be in damp horse-manure, though it 

 will breed in almost any kind of filth or decaying organic matter; for 

 this reason the name " filth" fly has been suggested. It is perfectly 

 obvious that if the eggs be laid, as they often are, in human excrement 

 from a person who is suffering or has recently suffered from typhoid 

 fever the flies, as they hatch and crawl out through the filth, may be cov- 

 ered with typhoid fever germs which may be carried to another person 

 in various ways. The disgraceful epidemics of typhoid fever that raged 

 in our army camps during the Spanish American war were probably 

 largely due to the lack of care in protecting the soldiers against this 

 kind of infection. In a similar way flies, by feeding on the sputum (as 

 they often do) of tuberculous persons, may carry the germs to other 

 persons. Knowing, now, the habits of the house-fly the methods of 

 fighting this serious pest are more or less obvious; they consist chiefly 



