﻿4 BULLETIN 14, U. S. DEPARTMENT OF AGRICULTURE. 



edges of piles. Here are some of the figures obtained from a count 

 of the pupae collected from different piles: 7,000, 1,500, 10,000, over 

 12,000, 4,500, 6,000, 6,700, 30,000, etc. 



In a recent article in the American Journal of Public Health, Levy 

 and Tuck make the following statement : " We therefore announce the 

 biological fact that the house fly does not pupate in manure if the 

 full-grown larvae can find any means of reaching and entering the 

 earth." They claim that "the adult larvae regularly leave the manure 

 heap" and that they "enter the earth whenever it is possible for 

 them to do so." To be sure, larvae may and often do burrow into the 

 ground before pupating — witness Dr. Terry's observations at Jack- 

 sonville, Fla., where he found larvae and pupae in the ground of soil- 

 floor stables — but that they do so regularly is open to serious question. 

 The figures given above are for puparia collected above the surface of 

 the ground and in the manure. After the removal of the heaps, 

 examination of the ground revealed only a very small percentage 

 beneath the surface. The fact that some were found there shows 

 that it was not the compact nature of the soil which prevented the 

 majority from burrowing and that there was no reason why all could 

 not have done so if such were their regular habit. It would seem 

 that Levy and Tuck have put too much emphasis on this one point. 

 A broader view, including all the phases of the migration of these 

 creatures, is necessary and will not detract from the importance or 

 value of the "maggot trap" which they have devised. 



It is quite certain that the migrating habit is deeply ingrained and 

 highly characteristic of housefly larvae. A consideration of the known 

 facts in the case will enable one to draw some inferences as to "the 

 stimuli or particular conditions" which determine this mode of 

 action. It has been noted that a sort of "wanderlust" seizes the 

 larvae just before pupation. It must be, therefore, that the migration 

 is initiated in response to internal stimuli incident to the maturing 

 of the larval stage and the onset of the metabolic changes preparatory 

 to the transformation to the pupal stage. The course and direction 

 of their travels are determined largely by external stimuli. It is quite 

 evident that as pupation draws near they flee the very moist regions 

 of a manure heap and seek the comparatively dry regions. If no such 

 dry places are to be found in the manure, they will leave it to pupate 

 in the ground or in cracks or crevices, under boards or stones, in loose 

 material of any kind. Dr. Terry found both larvae and pupae in the 

 soil of dirt-floor stalls. The larvae were found in that part of the 

 floor kept moist by the urine, while the pupae were found in a ring 

 in the drier soil outside the moist center. Further proof that moisture 

 acts as a stimulus in determining their choice of a place for pupation 

 is given below. 



