THE PHOTIC REACTIONS OF SARCOPHAGID FLIES 



211 



By inspection of table 7 it may be seen that Lucilia caesar 

 is much more strongly phototactic than Calliphora vomitoria, 

 for under all conditions the former turned more frequently toward 

 the single light or the larger area than the latter. It should also 

 be added that Lucilia caesar is far more reponsive to light, as is 

 evident from the following data. The average time that expired 

 between the moment when the head of the fly was protruded from 

 the mouth of the vial and the time of arrival at the side of the 

 cylinder, based on 25 reactions of ten individuals to the larger area 

 alone, was 8.1 seconds for L. caesar and 21.8 seconds for C. vomi- 

 toria. 



TABLE 7 



Summary of reactions of adult sarcophagids to opposing lights of the sa7ne intensity , 

 but form sources whose areas were as 1 to 7500. 



In view of these facts an answer may be given to the second 

 question proposed at the beginning of this section. The more 

 frequent presence of C. vomitoria in houses and like situations 

 is due chiefly to its relatively low degree of responsiveness to 

 light, so that odors from darker places may attract it more readily. 

 On the other hand L. caesar is very strongly phototactic and con- 

 sequently would seek the open, and if by chance it should find 

 its way into darker places its responsiveness to large luminous 

 areas would soon lead it to escape. It may be assumed that the 

 two species are equally chemotactic, which assumption is justified 

 at least by observation. Since C. vomitoria is less strongly photO; 

 tactic, individuals least so might easily be attracted into fairly 

 dark places, and would not soon be compelled to leave because of 

 their phototropism. 



