﻿THE MIGEATOEY HABIT OF HOUSEFLY LAEViE. 3 



pan are of two layers of screen wire 2 inches apart. Now it was 

 found in the very first experiments that larvae were escaping from 

 the cages, and it was seen that they found their way put through 

 the holes in the floor of the cages and also through the screens at 

 the sides. The numbers so escaping were surprising. It often 

 happened that several hundred crawled out of the cage during 24 

 hours. They were found in the vessels placed beneath the cages to 

 catch any drippings. By day the light was sufficient stimulus to 

 prevent them from crawling out at the sides, but at night they were 

 actually seen, with the aid of a flash light, making their way through 

 both thicknesses of screen wire and dropping into the vessel below. 



Moreover, in examining manure heaps on the open ground I have 

 many records showing this "tendency to congregate" at the edges 

 of the piles near the ground. About two cartloads of horse manure 

 had been piled out on the open ground for five or six days during 

 August, and at the end of this time it was hauled away. I examined 

 the ground where the heap had been and found many pupae, not 

 in the center of the area formerly covered by the heap, but around 

 the margin. Some were found on the surface, doubtless shaken out 

 of the manure at the time of removal; others were found buried a 

 half inch or more in the soil, where the larvae had burrowed just 

 previous to pupation. 



In another case some 50 cubic feet of manure had been heaped 

 up in a pile the base of which covered an area about 4 feet square. 

 After the pile had stood three days larvae were found swarming 

 in the warm, moist parts of the heap near the top and some distance 

 in from the sides. After eight days the entire pile was torn apart 

 and gone over carefully in search of pupae. None was to be found 

 in the upper parts of the heap where I had previously seen great 

 numbers of larvae. In fact none was found until the very lowest 

 layers were exposed. Here about 9,000 were collected. Not 

 more than 100 were found below the soil. The mass of pupae were 

 scattered in little heaps about the margin. They were just outside 

 the moist area of the manure, yet sufficiently protected from drying 

 and sunlight by the overhanging straw. The explanation of their 

 presence in such a position is, of course, that the larvae, just before 

 pupating, had migrated from the moist feeding grounds to a drier 

 region more favorable to the resting stage. The examination of 

 many other piles of manure showed the very same conditions existing, 

 the only difference being in the number of pupae collected. 



Altogether some 50 or more heaps of manure on open ground 

 have been examined. Each one contained from 40 to 50 cubic 

 feet of manure. Some contained much long straw, others very 

 little straw or bedding of any kind. The puparia are not hard to 

 find nor hard to collect because of their occurrence in masses at the 



