250 THE HOUSE FLY— DISEASE CARRIER 



of which lack legs. The leap is made by bringing the 

 two ends of the body together and suddenly releasing 

 them, like a spring. In this way it will sometimes jump 

 three or four inches. The species is cosmopolitan at 

 present, and it was doubtless originally imported from 

 Europe into the United States in old cheeses. 



Careful observations have been made on the life his- 

 tory of this fly by several writers. In 1892 Miss Mary 

 E. Murtfeldt studied the life history of the summer 

 generation in a western packing establishment. She 

 found that the eggs were laid in rather close clusters 

 of from five to fifteen, and were also deposited singly. 

 About thirty seem to have been laid by a single female. 

 The egg is white, slender, oblong, slightly curved, one 

 millimeter in length, and w^ith a diameter about one- 

 fourth of its length. It hatches in about thirty-six 

 hours, and the larva completes its growth in from seven 

 to eight days, reaching a length of seven to nine milli- 

 meters. Where food is sufficient the larva does not 

 move about, and groups of them will sometimes com- 

 plete their growth in the same crevice in which the 

 mother fly deposited her eggs. When full grown, how- 

 ever, the larva moves aw^ay to some dry spot, contracts 

 in length, assumes a yellowish color, and gradually 

 forms into a golden-brown puparium four or five milli- 

 meters in length. The adult fly issues in ten days. 

 Thus three weeks may complete the entire life cycle, 

 in August, in St. Louis. 



In Europe, Kessler found that the average summer 

 duration of this insect is four to five weeks, and states 



