﻿THE MIGRATORY HABIT OF HOUSEFLY LARV^l. 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 

 larvae 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 



