Rural School Leaflet. 827 



tion. They lie domiant during the winter, scarcely moving, until the 

 first warm days of spring when they leave their winter home. 



The first duty of the awakened, hibernating female house-fly is to 

 find a place to deposit her eggs. For this purpose she seeks a pile of 

 horse manure, but if this is not available she will lay them on almost 

 any kind of manure. She usually places them in horse manure because 

 it is the favorite food of the larva, the form of the insect that emerges 

 from the egg. The eggs are minute, whitish objects, about one-twen- 

 tijth of an inch in length, shaped like a grain of wheat. Each female 

 lays 100 to 150 eggs. It requires eight to twenty-four hours, depending 

 on the temperature, for the insect to complete its growth in the egg. 



The small larva that issues from the egg through the broken egg- 

 shell is footless, about as long as the egg, and is known as a maggot. 

 It is during the larval period that the insect feeds and stores up fat to 

 sustain it during its later life. At the end of a period of five to seven 

 days, the larva is fully grown and has moulted its skin three times. 

 The body is now about one-third of an inch long, pointed at the head 

 end and blunt at the other end. 



When the larva is fully grown it stops feeding. The body becomes 

 much contracted or shortened and barrel-shaped. The outer larval 

 skin is dried, wrinkled, hard, and brown in color. The insect shrinks 

 away from this brown skin, becomes entirely free from it, and uses this 

 skin simply as a shell to protect it during the striking changes it must 

 now undergo. The shell is the puparium. The short-bodied insect en- 

 closed in the puparium is the quiescent pupa. The pupa does not take 

 any food. It is during this stage that the legs and the wings are formed. 

 Five to seven days are required for the transformation of the pupa 

 into a fully formed fly. When this time is reached, the pupal skin is 

 moulted, freeing the fly, which breaks off the head end of the puparium, 

 escapes from it and from the pile of manure, and begins its life as a 

 winged insect. 



If the time required for each of the life periods given above be added 

 together, it will be found that ten to fifteen days are required for the 

 com[)lete development of a house-fly. This makes it possible for the 

 production of six to eight generations of flies during the warm months 

 from June to September. The mortality among insects is always high, 

 but if only twenty-five individuals from the 100 to 150 eggs laid should 

 reach maturity in each generation, the descendants of each wintering 

 female by the close of" the sixth generation would be over one 

 hundred thousand. This explains why house-flies may be so abundant 

 during the months of August and September. That they usually are 



