334 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



In discussing previous experiments reference was made to a method 

 utilized by the writer by which flies were allowed to mark themselves 

 by feeding on colored sugar syrup. Such flies were afterwards iden- 

 tified by the colored contents of the alimentary tract which showed 

 through the thin ventral membrane. When flies were sprayed at the 

 Laboratory the stain was applied with the bait pan attached. The 

 bait became highly colored with the fuchsin and flies fed on it both 

 while it was in the pan and after it was dumped. During the sum- 

 mer it was noted that the majority of flies on the Laboratory windows 

 showed that they had visited this colored bait. Such flies were also 

 frequently recovered in traps. Several times the abdominal contents 

 of flies from some of the traps placed in the Laboratory series were 

 squeezed out and ten to twenty flies would be found which had ap- 

 parently fed on the colored bait, though many times not enough had 

 been eaten so that the color showed through. This color usually 

 responded to the test for fuchsin given above. This was incidental 

 to the actual experimental work and no records of such flies appear. 

 Their number, however, always exceeded that of flies which had been 

 stained externally. This method of marking flies has obvious dis- 

 advantages and was first used as a makeshift for lack of other means, 

 but it does suggest a practical means of demonstrating the filth-to- 

 food habit of flies. By placing colored bait at a privy or garbage 

 accumulation any person can readily satisfy himself in this respect 

 as the stained abdomens show up quite brilliantly when flies are seen 

 on the windows. 



The advisability of spraying stained flies with some solvent or in- 

 tensifier of the stain used is a point worth emphasizing. At first 

 flies were examined before spraying, but this was not only tedious, but 

 a useless expenditure of time. Stained specimens could onlj' occa- 

 sionally be detected whereas catches which yielded no results by this 

 method were sometimes found to contain ten, twenty or even forty 

 marked flies. 



Summary of Data 



Laboratory Series 

 First lot of flies released, July 12. 

 Last lot of flies released, August IL 

 Number of lots released, 26. 

 TQtal number of flies released, 40,237. 

 Total Musca domestica released, 35,270. 

 Number of laboratory flies recaptured, 242.* 

 Number of stations at which recaptured, 45. 



* Musca domestica, 234; Phormia regina, 2; Muscina stabiilans, 6. 



