500 ANNUAL REPORT OF THE Off. Doc. 



are liatched. They begin feeding at once and tliiive and grow for from 

 five to seven days. At the end of this time, they crawl into the 

 loose ground or under dry boards or into dry places and enter the 

 pupa or resting state. This period occupies from five to seven days 

 and in some cases a little longer. Then the fly comes forth fully de- 

 veloped, the total life round requiring, therefore, from ten to four- 

 teen days. This time is Influenced somewliat by climatic conditions, 

 requiring a shorter or longer time, according to the cold or warmer 

 temperatures. Durng the Avinter the adult fly hibernates in some 

 warm or favorable place and becomes active again in the spring. 

 The size of the fly is also influenced to some extent during the larval 

 or growing period. If the larva are well fed, the flies will be full 

 grown. 



Prof. Wm. B. Herms, of the University of California, reports that 

 he has estimated the number of larva which had hatched in four 

 samples of manure, weighing in all fifte<?n pounds, and that 10,282 

 were found present. This would average about 085 larva per pound. 

 By estimating the weight of such a pile of manure, astonishing 

 figures can be obtained. Many other similar experiments have been 

 made, and it is easy to understand the reason why such great num- 

 bers of flies exist in the neighborhood of stables or places where de- 

 caying vegetable or animal matter is exposed. The Avay in which the 

 diseases mentioned are spread, is by the flies migrating from one 

 place to another, alighting upon all sorts of refuse material to ob- 

 tain their food and then, of course, going into the house, crawling 

 over our food, eating utensils, getting into milk and water, and also 

 by crawling over our bodies and sometimes getting into the mouth. 

 They are especially dangerous to infants where bottles and milk are 

 not kept covered or away from them. The legs and bodies of the 

 flies are covered with small hairs to which germs easily cling. 



Prof. Herms also reports that the number of bacteria which a 

 single fly may carry will reach all the way from a few hundred to 

 several millions and these germs, under favorable circumstances, 

 will live as long as twenty-three days. Early in the fly season the 

 numbers of bacteria are comparatively small, while later, this num- 

 ber increases greatly. The mouth parts of the common house fly 

 are not adapted to biting or stinging as is commonly believed. Other 

 species of the fly, one of which is the stable fly, has a mouth part so 

 constructed as to be able to pierce the skin. This form of insect can 

 inject disease into the blood directly. The danger in the flies which 

 infest our dwelling places lies in their power to carry germs on their 

 bodies to food as above stated. Typhoid fever is one of the most 

 serious diseases of man, and because the fly has been so energetic 

 in transmitting this ailment, Dr. Howard has called this insect 

 the "typhoid fly." Typhoid fever has been prevalent in many of our 

 army camps, and it is now known that it was caused by the large 

 number of flies, which, in turn were caused by the unsanitary man- 

 ner in which the camps were cared for. During the Spanish American 

 War, the Army Surgeons were especially energetic in their campaign 

 against sickness, and by eliminating all sources of breeding places, 

 typhoid fever was reduced to a minimum. From all the information 

 we can gain on the subject, it is clearly evident t\mt if we are to 



