THE MIGRATORY HABIT OF HOUSEFLY LARV^. 5 
It is well known that they avoid light, and the rapidity with which 
they disappear from view when exposed to light through the disturb- 
ing of their feeding grounds is a familiar sight. The observation 
mentioned in which larvae were seen crawling out through the screened 
sides of cages at night, but never during the day, is a case in point. 
They avoid the extremely hot portions of manure heaps. Ther- 
mometers inserted from 6 to 12 inches toward the center of a heap 
will register anywhere from 110° F. to 170° F., which, of course, 
would be fatal. The hotter the pile the nearer the surface are the 
larvaB to be found. They also avoid the moldy parts of the heap. 
They seek, as it were, the safety of the middle region between the 
heat and mold of the center and the exposure to sunlight and dryness 
of the exterior. Doubtless other conditions also have an influence 
in determining their actions. 
The habit of seeking the comparatively dry regions near the edge 
of manure heaps at the time of pupation is an adaptation of great 
advantage in that the adult fly at the time of emergence is thus 
afforded an easy path to freedom. It prevents the drowning of the 
imagines and insures the quickest possible expansion and drying of 
the wings. At least this is the teleological explanation. Yet it can 
not be claimed that these are intelligent acts, nor that the future is 
consciously provided for. We have here indeed a "battalion of 
somnambulists" acting in blind response to various internal and 
external stimuli. 
THE BEARING OF THE MIGRATORY HABIT ON THE PROBLEM 
OF CONTROL. 
So far as I have been able to determine, Levy and Tuck were the 
first to take advantage of the migratory habit in an attempt to destroy 
the maggots. In their paper published in July, 1913, they report 
two experiments. In the first they placed manure in a barrel in the 
bottom of which several holes had been bored, with the result that 
on the following day thousands of maggots were found in the tub 
placed beneath, and the number seemed to increase for three days. 
In a second experiment the bottom of the barrel was replaced by- 
stout wire gauze. The results of this trial are not given. 
It was not until the beginning of November that I learned of their 
work, and it was near the end of the month before I had an oppor- 
tunity of reading the article. I had already carried out two experi- 
ments during the summer at Arlington, Va., and others during the 
fall at Audubon Park, New Orleans, La. The possibility of taking 
advantage of the migrating habit was suggested to me by experience 
with larvae escaping from cages used in other experiments. The 
results of the experiments were beyond my best expectations, and 
