June, '16] EVANS: BREEDING HABITS OF COMMON HOUSE-FLY 359 



feeding in old rags which had been fouled with excreta. The excreta 

 in this case probably furnished enough food for the development of the 

 larvae. It seems quite probable that flies might lay directly in rags 

 under such conditions but the writer does not believe that flies will 

 lay eggs in rags which do not contain a food supply. Without a food 

 supply the larvae would have to migrate or perish. It is very unlikely 

 that flies would lay eggs where food would not be plentiful for the 

 larvae, especially with food so abundant as it is during the summer. 

 Migration from a breeding place without food to a food supply would 

 undoubtedly result in the death of many larvae unless the food supply 

 was very close; in which case the eggs would very likely be deposited in 

 the food supply when laid. 



During the course of the various experiments it was noticed that the 

 larvae W£re especially sensitive to an excess of moisture. If too much 

 of the solutions was added to the media the larvae invariably would 

 leave the media and go into a drier portion of the vessel. This was 

 also noticed in the examination of the wetter portions of manure piles 

 and especially the deeper, wet portions of bins. Although most of the 

 bins examined were found to be faulty in construction so that many 

 flies could gain access, yet the number of larvae present were few. They 

 were found to be prevented from breeding in the upper layers due to a 

 layer of mold which developed over the top of the manure after it had 

 stood for a short time in the bin. Its excellent development here is 

 probably due to the constant temperature furnished by the fermenting 

 of the manure below. Cow dung as dropped in the pasture was 

 examined, as it was known to be saturated. No larvae were found in 

 the manure but they were sometimes present in the layer of earth just 

 beneath the manure. The eggs were found to be deposited at the 

 base of the pile near the ground into which the larvae were able to enter 

 soon after hatching. In this position beneath the pile the larvae are 

 kept supplied with food which seeps down from the pile above. The 

 very few larvae in cow manure indicate that it is not one of the favor- 

 able places for fly breeding. This probably is due largely to the 

 amount of moisture that it contains as well as the compact form in 

 which it is found. 



Very little of the work which has been done on the fly deals with its 

 relationship to garbage. During the summer months this is one of the 

 problems of every city. Hundreds of flies swarm about exposed gar- 

 bage. Their mission seems to be one of feeding rather than breeding. 

 If one examines the manure heaps during the summer even more 

 flies are found to be present. This is their real breeding place. Only 

 one garbage pail was found during this work which contained larvae. 

 This contained a quantity of sardines and was teeming with maggots. 



