A MAGGOT TRAP IN PRACTICAL USE. 
11 
not as thoroughly as on the former occasion, but there were found at 
the fresher end of the pile at least four nests of several hundred puparia 
each. It is not possible to estimate the percentage destroyed, but it 
was quite plain that the trap was not as effective during the autumn 
as in the summer. This may have been due partly to carelessness in 
the matter of watering the heap, but more probably to the lower air 
temperatures of this period. When the outside temperature is low, 
the difference between the air and the temperature of the manure 
heap is so great that the larvae will not leave the heap; and if the low 
temperatures prevail for a long period the larvae will eventually 
pupate in the manure. The following experiment shows the effect 
of low air temperature. This experiment was conducted at New 
Orleans, La., in December, 1913. A small wire basket was filled 
with fresh horse manure on December 1 and was continually exposed 
to flies. The number of larvae caught and the temperature during 
the period are tabulated below. 
Experiment to show effect of low air temperature in preventing migration of house-fly 
larvse, New Orleans, La., December, 1913. 
Number 
of larvse 
caught. 
Mini- 
mum 
tempera- 
ture. 
Maxi- 
mum 
tempera- 
ture. 
Mean 
tempera- 
ture. 
Dec. 2 
12 
15 
47 
199 
745 
F. 
56 
57 
56 
57 
48 
40 
32.5 
34.5 
38 
41 
An 
58.5 
49 
50 
52 
55.5 
51 
° F. 
74 
67 
68 
73 
70 
61 
61 
50 
56 
59 
65 
68 
73 
66 
62.5 
69 
60 
58 
° F. 
65.5 
3 
61.5 
4 
62.5 
64.5 
6 
63.5 
7 
55 
X 
14,000 

1 
43 
405 
1900 
55 
C) 
41 7 
10 
45.3 
11 
48.5 
12 
53 
13 
53 
14 
65.8 
15 
i 700 
115 
L85 
160 
32 
57.5 
16 
56.2 
]7 
60.5 
is 
57.8 
19. . 
i Approximate. Counts of Dec. 8 and 15 include catch of preceding day. 
Probably most of those that were caught on December 8 had 
migrated during the night of December 6. Not much migration from 
the manure takes place during the day, because of the maggots' nega- 
tive reaction to light; therefore the minimum temperature is probably 
more significant than the daily mean temperature. It will be seen 
from the table that minimum temperatures of 40° F. or less will stop 
all migration from the heap. 
It may be said, then, that the maggot trap has another defect in 
that it is not effective when temperatures are low, and that it is not 
at all effective when the air temperature is below 40° F. 
