BEHAVIOR OF FIRE FLIES 257 



Odontosyllis enopla, just before mating, which probably occurs- 

 periodically about every 26 days during several summer months, 

 the females are found at dusk swimming about near the surface 

 of the water. At first they are only very slightly luminous, but 

 later they quite suddenly become acutely phosphorescent, par- 

 ticularly in the posterior three-fourths of the body. At this 

 phase they swim rapidly through the water in small, luminous 

 circles two inches or more in diameter. "The male first appears 

 as a delicate glint of light, possibly as much as 10 or 15 feet from 

 the luminous female. They do not swim at the surface, as do 

 the females, but come obliquely up from the deeper water. They 

 dart directly for the center of the luminous circle and 

 seize the female with remarkable precision, when she is in the 

 acute stage of phosphorescence." No more light is produced by 

 either individual after mating. Galloway leans toward the opin- 

 ion that the luminosity in the male is useless and that phosphor- 

 escence is a by product of a form of metabolism. I assume he 

 would maintain that the origin of this phenomenon was acci- 

 dental and had no connection with its present function in mating. 



In all other instances the conclusions as to the function of 

 luminescence are either purely speculative or are based mainly 

 upon structural evidence such as the more highly developed 

 and larger eyes in the active male fire-flies as compared with 

 the relatively small ones in the comparatively inactive females. 

 Mangold says (1910, p. 328), "Leider sind wir in der Frage nach. 

 der okologischen Bedeutung des Leuchtens fast ausschliesslich 

 auf Hypothesen angewiesen." 



It is not my purpose to review the very extensive literature 

 on the subject, of luminescence in organisms in its different 

 phases. This has recently been very well done by Mangold 

 (19 10) who has brought together in his bibliography 649 titles, 

 an enormous number, testifying to the general interest in the 

 subject. 



MATERIAL 



I took up the study of the behavior of fire-flies 2 in the neigh- 

 borhood of Smithsburg, Western Maryland, early in June, 191 1. 



2 Dr. F. H. Chittenden of the Bureau of Entomology, Washington, D. O, kindly 

 identified a number of specimens of fire-flies captured at Smithsburg and pro- 

 nounced them to be Photinus pyralis. Among these specimens there were some 

 which were much smaller than others of the same sex, and I was of the opinion 

 that they represented a different species. Dr. Chittenden, however, concluded 



