84 THE HABITS AND BIOXOMICS OF THE HOUSE-FLY 



While these results arc interesting further experiments would 

 be required before any general conclusions could be drawn'. 



Hibernation. 



The disappearance of Hies towards the end of October and 

 during November is a well known fact and the question is fre- 

 quently asked, what becomes of them ? Observations on this 

 question were made from the beginning of my study of this insect. 



Three causes contribute to the disappearance of the flies, 

 namely, retreat into hibernating quarters or into permanently 

 heated places, natural death and death from the parasitic fungus 

 Empusa miiscae. The last cause of disappearance is fully con- 

 sidered later and it accounts for a large proportion of the summer- 

 bred flies. The natural death of flies may be compared, I think, 

 to the like phenomenon that occurs in the case of the hive-bee. 

 Apis meUifica, where many of the workers die at the end of the 

 season by reason of the fact that they are simply worn out, their 

 function having been fulfilled. The flies which die naturally have 

 probably lived for many weeks or months during the summer and 

 autumn, and in the case of the females have deposited many 

 batches of eggs ; their life work, therefore, is complete. Those 

 flies which hibernate are, I believe, the most recently emerged, and 

 therefore the youngest and most vigorous. On dissection it is 

 found that the abdomens of these hibernating indixiihials are 

 packed with fat cells, the fat-body having developed enormously. 

 The alimentary canal shrinks correspondingly and occupies a very- 

 small space ; this is rendered possible by the fact that the flv does 



1 Kindle (191B) has more recently carried out a series of experiments in which 

 strips of coloured cardboard \yere exposed to catch flies which settled on them. 

 The experiments appear to demonstrate that the flies did not display any marked 

 colour preference. 



