Apr. IS, i9i8 Overwintering of the House Fly 155 



had continued and flies were present all winter in the animal house 

 (see pp. 156-157) and that they escaped from the house on mild days 

 during March and early April. 



It will be noted that these observations on wild flies under outdoor con- 

 ditions agree very closely with the experimental results with caged flies. 

 Uncaged flies disappeared at about the same time that the caged flies were 

 killed by the cold in early December. 



UNHEATED BUT PROTECTED SITUATIONS 



A very favorable unheated but protected location was found in one of 

 the stables of the Arlington farm. This stable was at the west end of a 

 long building and vms protected on the north and east by a stone wall 

 and high ground. The entrance was at the west and the ceihng was low 

 and tightly boarded. Flies were collected at frequent interv^als as late as 

 January 19, 191 5. Many of these were found with the ptilinum still 

 exserted, showing that they were freshly emerged. Puparia were found 

 in an accumulation of material under one of the feed troughs, and from 

 them flies were emerging. All flies completely disappeared, however, 

 after January 19 and none were again taken here until April 30, 191 5. 



At Bethesda, Md., no house flies were taken in unheated stables from 

 December 7, 1915, till April 27, 1916. During the winter of 1914-15 

 collections were made in the attic of a dwelling house on the Arhngton 

 farm, and during the next two winters a careful watch was kept in the 

 attics of one or two dwelling houses and of the apicultural laboratory at 

 Drummond, Md. No house flies were found in such locations, although 

 Pollenia rtidis was present throughout the entire winter each season. 



The experimental results showed that attics and slightly heated stables 

 and similar places off'er the most favorable temperature conditions 

 conducive to longevity. Yet observations indicate that house flies never 

 select such places for spending the winter. The records given by Copeman 

 and Austen (4) of flies sent in to them from various places in England 

 include no specimens of house flies taken in dormant or inactive condition 

 in attics or other unheated places. It is shown that they "were all taken 

 in an active condition" and from heated locations, such as dining rooms, 

 kitchens, or bake shops. 



IN HEATED BUILDINGS 



Copeman and Austen (4) pointed out that — 



under the exceptionally favorable conditions afforded by confectioners' shops and 

 restaurants, house flies of both sexes may survive in some numbers, at any rate until 

 February. 



But there is — 



nothing in the shape of proof that female house flies found alive at the end of the 

 winter actually survive until oviposition takes place. * * * The ultimate fate 

 of these insects is however at present tinknown. 



