October, '17] HOWARD: HIBERNATION OF HOUSE-FLY . 467 



exposure for one week at 30° F. and one female survived a week's 

 exposure to 40° F.; all others died even with these short exposures. 

 Of the larvse, none survived a week's exposure to 12° or 30° F., but 

 three larvse survived one week's exposure to 40° F. and two adults 

 emerged, the third dying. Longer exposures at 40° F. were fatal. 

 Pupse were killed in one week at 12° F.; at 30°, 23 survived and pro- 

 duced adult flies, but all died at longer exposure than one week; at 

 40°, 21 survived and produced adults, but none were able to endure 

 more than one week of such cold. 



The objection may be raised to this that the change from the out- 

 door temperature of July to that of the refrigerator was too sudden. 

 The double packing of the cases would tend, however, to reduce this 

 danger and make the change more gradual. It would seem from 

 these observations that the house-fly in all its stages is very sensitive 

 to low temperatures, a temperature of even 40° F. causing death if 

 long continued. 



To further test the ability of larvse or pupae to survive our winters, 

 several thousand half-grown to full-grown larvae were secured on 

 October 15, 1915. An outdoor breeding cage 4x4x5 feet was trans- 

 formed into a manure heap. Four twelve-inch flower pots were sunk 

 in the soil and filled with fresh manure. Into these were placed the 

 fly maggots, after which a covering of about twelve inches of fresh 

 manure was placed over the entire floor of the cage. The larger 

 maggots pupated very soon and large numbers of flies emerged before 

 frost came. On May 15, 1916, after several Lucilia and Saixophaga 

 had emerged, the manure was removed and the contents examined. 

 About 25 per cent of the puparia had not produced adults in the 

 autumn previous, but in every case these had died and the contents 

 begun to decompose. 



In the springs of 1914 and 1915 careful searches were made about 

 manure piles and compost heaps on the University Farm and else- 

 where, but not a single live puparium was found in the manure or 

 surrounding soil. In the spring of 1917 a third attempt was made to 

 find puparia. The manure from the University Farm stables is placed 

 in a compost heap which by autumn reaches a size of about two 

 hundred feet long by three to ten feet high and fifteen feet wide. 

 On April 17 a few puparia were found in the dry manure on the east 

 edge of the pile, but more in the soil under the center, near the north 

 end, where the manure was about three feet deep. They all looked 

 quite fresh, some still possessing a ruddy or yellowish color. A total 

 of 1,646 of these apparently live pupae were collected and taken to the 

 laboratory. By May 15 not an adult M. domestica had emerged, 

 although one Scatophaga stercoraria and one Sarcophaga sp. had 



