22 BULLETIN 1453, U. S. DEPARTMENT OF AGRICULTURE 



In a storage room containing cured meat, flies of both sexes were 

 always found upon the screen covering the only window, but there 

 were more flies on the meat, even in dark corners of the room, than 

 on the window. A few flies have been observed in the smoke cham- 

 ber of an abattoir after the smoke was dissipated. The darkness of 

 any storage room seems to be ineffective as a repellent in the pres- 

 ence of the overwhelmingly attractive food odors. 



Mated females confined in shell vials in an incubator oviposited 

 profusely on ham; the fact that the interior of the incubator was 

 absolutely dark did not hinder reproduction in the least. Murtfeldt 

 (53 ', p. 174) stated that the flies are not active at night but are able 

 to work in partially darkened places; Kellogg (37, pp. 114-115) re- 

 corded flies swarming in smoky compartments; and Sakharov (67) 

 believed that fish may be infested during the smoking. 



In discussing the behavior of adults of Piophila casei it is ap- 

 propriate to refer again to the interesting habit of combat between 

 adults. This was observed by Ruhl (66), who could find nothing 

 similar recorded. Combat does not always appear to arise from 

 the frenzied impulse of the males to mate; adults often spar and 

 maul one another, apparently purely as a means of discharging their 

 superabundant energy. 



Bachmann (9) has given an extended account of his observations 

 on the behavior of the flies in their fighting and mating. He ob- 

 served severe fighting in which combatants were injured and even 

 killed. Fights do not occur, he stated, in a group of flies contain- 

 ing only females, and the writer has made the same observation. 



It is a rather common occurrence to observe adults, confined in a 

 vial, sham death for a few seconds when the container is jarred. 



THE EGG 



The egg is opaquely white, very smooth and shiny, slightly curved and 

 roundly pointed at the ends. The length is usually about 0.6 millimeter. The 

 appearance of freshly laid eggs upon lean ham is shown at A in Figure 3. 



INCUBATION PERIOD 



A few observations have been made by other writers on the dura- 

 tion of the egg stage. Kellogg (37, pp. 114-115) found that eggs 

 hatched after 4 days; Murtfeldt (53, p. 173), after 1% days; Mote 

 (51, p. 310) recorded incubation periods of from 23 to 54 hours; 

 whereas Sakharov (67) gave the duration of the egg stage as 2 days. 

 The writer has observed periods as short as about 23 hours, and dur- 

 ing the hot months hatching may usually be expected after about 

 1 day. 



HATCHING 



When the egg hatches, the larva slowly works its way out of the i 

 eggshell through a small longitudinal slit in the anterior end of the 

 egg. The empty shells collapse and are opaque, white, and con- 

 spicuous in contrast with the red color of ham. 



THE LARVA 



The larval stage is the most destructive and most resistant stage 

 of the insect. It is the stage which has engaged the attention of a 



