46 



PRINCIPAL HOUSEHOLD INSECTS. 



top of which was covered with gauze, and twenty flies introduced. 

 This was at noon; by 4 o'clock in the afternoon no eggs could be found, 

 but at 9 o'clock the next morning two clusters of eggsliells, one cluster 

 containing 26 and the other 45 eggs, were found. The eggs had been 

 deposited in small cavities between the sides of the vessel and the 

 manure, at a depth of about a quarter of an inch below the surface, 

 but were not arranged in any regular order. Afterwards several black- 

 berries, cherries, and partly decayed apples were placed in this vessel, 

 and more flies were introduced. A single ei^g was found the next day 

 on the upper side of one of the blackberries. At a later date experi- 

 ments were tried in the same jar Avith fresh cow manure. Apparently 

 no eggs were deposited until the third day, when two small clusters 

 were observed. These hatched in due time, but all the larva' died 



before attaining full growth. 



These exj>eriments were 

 hardly extensive enough to al- 

 low us to generalize, but so far 

 as tliey go they seem to show 

 that horse manure is the favorite 

 breeding i^lace of the house fly. 

 Continuous observations made 

 upon the offspring of flies which 

 bred most freely in this last- 

 named substance indicated that 

 the larva? molt twice and that 

 there are thus three distinct 

 larval stages. The periods of 

 development were found to be 

 about as follows : Egg from de- 

 I)osition to hatching, one-third 

 of a day; hatching of larva to first molt, one day; first to second molt, 

 one day; second molt to pupation, three days; pupation to issuing of 

 the adult, five days; total life round, approximately ten days. There 

 is thus abundance of time for the development of twelve or thirteen 

 generations in the climate of Washington every summer. 



The number of eggs laid by an individual fly is undoubtedly very 

 large, averaging about 120, and the enormous numbers in which the 

 insects occur is thus plainly accounted for, especially when we consider 

 the abundance and universal occurrence of appropriate larval food. 

 The different stages of the insect are well illustrated in the accompany- 

 ing figures and need no description. 



Taschenberg in his Praktische Insektenkunde, iv, 1880, 102-107, gives 

 a good popular account of the house fly, but leaves the impression that 

 the duration of a generation is much longer than we have indicated. 

 He also states that the female lays its eggs on a great variety of sub- 

 stances, particularly on spoiled and moist food stuffs, decaying meat, 



Fig. Ib.—Musca domestica: a, pupa removed from 

 pupariura ; b, hiud end of body of larva in second 

 stage; c, anal spiracles of larva iu first stage— all 

 enlarged (original). 



