October, '17] HOWARD: hibernation of house-fly 465 



well-known fact, first brought to notice probably by Jepson in 1909 

 when he bred them in a greenhouse. Since the winter of 1914-15 flies 

 have bred each winter in the animal room connected with the Minnesota 

 University Insectary, the construction being such that the accumula- 

 tion of material suitable for fly breeding can be scarcely avoided. 

 Up to the winter of 1914-15 the same conditions held in the bac- 

 teriological animal house of the University. The droppings of rabbits 

 and guinea pigs collected in corners and not being cleaned out for 

 long periods, furnished breeding places for both M. domestica and a 

 few Stomoxys calcitrans. Breeding places were also found under 

 water dishes where the spilled water soaked the bedding thus setting 

 up fermentation. Regular and more thorough cleaning quickly 

 remedied this condition. 



Several observations have been recorded to prove that adult house- 

 flies are rarely taken in winter in buildings or other protected places. 

 In 1913 Copeman reported on three collections of hibernating flies 

 taken in England during March and April. Not a single specimen 

 of the house-fly was found in these collections. In 1914 Copeman and 

 Austen reported on fifty-eight consignments of hibernating flies sent to 

 them from widely distant parts of England. Out of a total of ninety- 

 four flies, twelve proved to be M. domestica. These were taken during 

 January, February and March, each time in an active state in living 

 rooms or heated rooms. Ashworth, 1916, states that no adult house- 

 flies can be found in Scotland during the winter. 



Since most of the observations on this subject have been made under 

 climatic conditions somewhat milder than those found in Minnesota, 

 with the exception of those by Hewitt at Ottawa (1915), data collected 

 here during the past three years may be of interest. 



Temperatures in Minnesota often reach — 25° to — 30° F. and remain 

 below zero over considerable periods in mid-winter. Flies continue 

 to breed in Minnesota until late in October or early November, the 

 adults lasting until the first heavy frost in November when those die 

 which have not been previously killed by Empusa muscce. Individual 

 adults of both sexes have been taken during the months of December, 

 January, February, March and April, always in houses, or restaurants 

 where temperature and food conditions would be favorable. In 

 stables flies of several species begin to appear by mid-April as a rule, 

 but the house-fly has never been taken among these early forms. A 

 total of nineteen flies have been taken in this way, eleven females and 

 eight males. These flies always looked fairly fresh with wings un- 

 broken. The number seems almost negligible, but when we consider 

 the limited field of observation of one or two people, there must be a 

 fairly large number of flies thus surviving each winter. Flies do not 



