﻿THE MIGRATORY HABIT OF HOUSEFLY LARVJS. 



9 



breeds preferably in horse manure, but it has never been determined 

 just how long a given lot of manure continues to be an attractive place 

 for egg laying, nor for how long a period fly larvae will continue to 

 appear in it. It is obvious that the maggot trap would not be prac- 

 tical if the infestation of the manure were daily renewed for a long 

 time. Under ordinary conditions the dryingof the surface of a heap 

 of manure probably limits the period of egg laying to the first day or 

 two of exposure. But in a maggot trap the manure must be kept wet 

 in order to insure the greatest amount of migration. Would not such a 

 moist surface be daily reinfested and maggots continue to appear in 

 the manure as long as any fermentation were in progress? As a 

 matter of fact, the period of infestation appears to be rather short, 

 and even under the most favorable conditions maggots will rarely be 

 found in a- given lot of manure after 10 or 12 days' exposure. In 

 support of this claim some experimental data may be given here. 



A fourth experiment was carried out in the same manner as exper- 

 iment No. 3, except that no cage was used to cover the trap at any 

 time. The manure in the basket was thus continuously exposed to 

 flies and the surface was kept moist by daily sprinkling. The larvae 

 were removed from the pan each day and counted and the pan was 

 again partly filled with water. The manure used was taken from 

 stables on November 12 and the experiment started on the same date. 

 Larvae began to appear in the pan on November 13 and continued 

 daily to the 24th, as shown in Table IV. 



Table IV. — Migratory habit of housefly larvse; Experiment No. 4. 



Date. 



Larvse 

 caught. 



Date. 



Larvse 

 caught. 



Nov. 13 

 14 

 15 

 17 

 18 

 19 



14 



2,230 



16,000 



15,000 



2,530 



2,070 



Nov. 20 

 21 

 22 

 23 

 24 



1,040 



560 



465 



140 



36 



i Approximate. 



The manure contained little straw or other bedding and was very 

 attractive to the flies as evidenced by the heavy infestation (about 

 20,000 from a little more than a bushel of manure). Yet no larvae 

 were to be found in the manure after 12 days. 



Examination of heaps of manure on open ground has shown in 

 many cases that at the end of eight days only pupae were to be found 

 in the manure. Even in cases where the manure was especially 

 attractive to the flies, by reason of active fermentation and the 

 absence of straw, all were found to have reached the pupal stage by 

 the tenth day. Any device for applying the principle of the maggot 

 trap on a large scale must take this time factor into consideration. 



