8 NEW YORK STATE MUSEUM 



Description. The tgg of the house fly is a slender, whitish object, 

 grooved on one side somewhat like a grain of wheat, and only one- 

 twentieth of an inch long. 



The maggot or, more properly, larva, is whitish, at first very 

 small, and when full grown about one-third of an inch long. The 

 body tapers from the large, nearly truncated posterior extremity to 

 the slender head. 



The resting or transforming stage, known as the puparium, is 

 oval, brownish, ringed and scarcely one-quarter of an inch long. 



Habits. The house fly breeds by preference in horse manure, 

 though it occurs to a limited extent in cow manure, human excre- 

 ment and miscellaneous collections of organic matter. 



It winters in the latitude of New York probably mostly as a 

 larva, possibly sometimes in the puparium. The work of Dove * in 

 Texas shows that even in that southern latitude the house fly does 

 not winter as an adult, though when breeding media have a tem- 

 perature of from 46° F. to 65° F. adults may emerge from puparia, 

 a process Avhich may continue through most of the winter during 

 mild weather. Repeated observations in New York State convince 

 the writer that the house fly appears relatively late in the spring, 

 from early May to June. There is, following issuance, an interval 

 known as the preoviposition period, during which no eggs are de- 

 posited. This may range in Texas from 4 to 20 days, the usual 

 time during the summer being from about 4 to 9 days.^ The eggs 

 are deposited upon manure and other suitable material. The flies 

 penetrate to only a very slight extent into dimly lighted or dark 

 places in order to deposit eggs.^ 



The maggots hatch in less than 24 hours, and complete their 

 growth under favorable conditions in from 5 to 7 days. The white, 

 conical maggots, then about one-third of an inch long, transform to 

 oval, brown puparia and remain in this condition from 5 to 7 days. 

 The life cycle is therefore completed in from 10 to 14 days, the 

 shorter period being true of the warmer part of the year, especially 

 in the vicinity of Washington, D. C, and farther south. One fly 

 may deposit 120 eggs, and there may be 10 or 12 generations. 



Recent observations^ show that the maggots or larvae thrive only 

 in substances which are more or less alkaline, and that they are 

 unable to develop to maturity in the presence of comparatively 

 small amounts of organic or other acids. They are also sensitive to 



*Jour. Econ. Ent., 9:528-38. 1916. 



5 Bishopp, Dove & Parman. Jour. Econ. Ent, 8:54-71. IQIS- 



s Felt. Jour. Econ. Ent., 3 :24-26. 1910. 



7 Evans. Jour. Econ. Ent., 9:354-62. 1916. 



