J. E. M. Mellor 59 



adults do remain dormant in cold and sheltered situations. He considers 

 that insufficient attention has been paid to the accurate identification 

 of species found. That this may often be the case is shown by the obser- 

 vations of Copeman (1913) already quoted. 



In 1914 Copeman and Austen, as a result of examination of 58 

 consignments of flies, sent from all parts of England, only found 

 M. domestica to appear 12 times, of which 9 were observations of 

 single specimens, one of the remains of 11 dead flies (Appendix, Serial 

 No. 4), one of several specimens reported in a baker's shop (App. Ser. 

 No. 17), and one of a single specimoi reported to have emerged from a 

 stable manure heaj) near the house, from which it was thought possible 

 to obtain several flies on any mild day throughout the winter^. 



From the results of this investigation the writers consider that the 

 customary explanation of the perpetuation of the house-fly by over- 

 wintered adults had been fairly tested and found to fail. They therefore 

 suggested looking for pupae during the winter in places where adults 

 were known to have been abundant during the previous summer and 

 autumn. 



In an earlier part of the paper they suggest that the relative lateness 

 of the season, in which the house-fly becomes abundant, may be due to 

 the fact that only small numbers of adults overwinter, and that there- 

 fore it requires time for the numbers to increase to any importance. 

 They remark, however, that "there is as yet nothing in the shape of 

 proof that the female house-flies, found alive at the end of winter, actually 

 survive until oviposition takes place." As regards this, Graham-Smith 

 (1914) has shown that the increase in numbers of flies in autumn is 

 closel}^ connected with the temperature recorded by the 2 foot ground 

 thermometer, and (1916) that the sudden disappearance towards winter 

 is due to the non-emergence of flies from pupae, owing to the temperature 

 falling below the critical point necessary for the emergence of M. 

 domestica. 



Graham-Smith (1914), though he has not actually found the pupae 

 of M. domestica during the winter, records observing numerous blow- 

 flies {CaUi'phora erythrocephcda), which seemed to have freshly emerged, 

 on sunny days at the end of February 1914, in sheltered gravel pits 

 far from houses. In April and May 1913 he bred Sarcoj>haga melamira 

 and Anthomyia radicum from samples of dog's faeces, collected in the 

 autumn of the previous year. And, moreover, on March 28th, 1914, 



^ Possibly the heap and its environs contained many pupae from which those flies 

 emerged at intervals during winter, and the remainder in summer. 



