BIOLOGY OF SOME COMMON LAMPYRID/E. 43 



and on both occasions the entire valley, for a moment, was a 

 blaze of flashing lights, and then for a moment it was in darkness, 

 except for an occasional flash, which seemed to come from fire- 

 flies of different species than those that were flashing in unison. 

 The fireflies in this particular locality were almost entirely of the 

 species Photinus consanguineus , and at each period of flashing 

 both males and females were observed to emit light. On both 

 nights this phenomenon occurred shortly after it became dark, 

 at approximately 9:00 P.M. On the first night the phenomenon 

 was observed for approximately fifteen minutes. How much 

 longer it continued after that was not determined. By very 

 careful observation it was discovered that each period of flashing 

 started on the crest of the hill at the south side of the valley, 

 by one, or only a very few flashes, and that the impulse stimu- 

 lated by these few insects instantly appeared to sweep over the 

 valley, resulting in the great mass of flashing lights. On the 

 second night an experiment was performed in which it was 

 discovered that, by standing on the side of the valley and causing 

 short flashes with a pocket flash-light, the fireflies of the entire 

 valley responded. At first, after estimating the length of the 

 latent period, the flash-light was flashed just before the normal 

 time for the fireflies to flash, with the result that the entire mass 

 of fireflies responded. Then two flashes were emitted from the 

 pocket flash-light with the interval between flashes reduced to 

 about three fourths that of the normal flashing period, and the 

 fireflies responded with apparent equal results. Finally, the 

 period was reduced to approximately one half the normal time. 

 The fireflies as a mass appeared to respond to the first short 

 flash. The second time a large per cent of them responded, 







but after this second short period, the flashing in unison was so 

 disturbed that each insect flashed independently of the flashing 

 period of the others. Blair (1915), in commenting on the 

 reason for the synchronous flashing of fireflies, states: 'The 

 flashing in unison is too regular to be caused by chance puffs of 

 wind. A more probable explanation of the phenomenon is 

 that each flash exhausts the battery, as it were, and a period of 

 recuperation is required before another flash can be emitted. 

 It is then conceivable that the flash of a leader might act as a 



