THE MIGRATORY HABIT OF HOUSEFLY LARVAE. 
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 laving, 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 drying «of 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 larvae; Experiment No. 4. 
Date. 
Larvae 
caught. 
Date. 
Larvae 
caught. 
Nov. 13 
14 
Nov. 20 
1,040 
14 
2,230 
21 
560 
15 
16,000 
22 
465 
17 
15,000 | 
23 
140 
18 
2,530 
24 
36 
19 
2,070 
1 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. 
