March, ig 1 7.] WiLLIAMS : NoRTH AMERICAN LaMPYRID^. 23 



the voracious appetite of Photuris, it does not flourish alongside its 

 larger neighbor. Only a few Photuris were found in the Photinus 

 consanguineiis locality. As in other Lampyridse, Photuris has more 

 or less well-defined centers of distribution, areas fairly scintillating 

 with their lights, which elsewhere are more scattered or absent. 

 These places, where on favorable evenings the larvae can be found 

 in abundance, are evidently the ones in which they pass their early 

 stages. 



Both sexes of Photuris fly readily and rather high, but the males 

 are more often seen on the wing than the somewhat terrestrial 

 females. In July, the flight begins from a little before to a little 

 after 8:00 P. M., and most of the males have settled by 9:00 P. M. 

 While there is considerable uniformity as regards the number of 

 flashes emitted by these insects, exceptions are common. As a rule, 

 the males flash three or four times to a period, and the last flash is 

 usually the least intense. Each flash is of about a second's duration, 

 and separated from the next by considerably less. Some flash twice, 

 another will give six very rapid flashes, but the number seems con- 

 stant for each specimen. It was estimated that when in flight, the 

 males flash for every fifteen feet traversed. They may scintillate 

 in this manner when resting on trees or weeds. The flight of the 

 female is more rapid and direct than that of the male, and her flashes 

 are less intense and somewhat more variable. While on the wing she 

 was observed emitting a dim though steady light. When alighted 

 she flashes once or several times. In the latter case the intervals 

 are longer than in the male. 



While there seems to be little doubt that the light emissions play an 

 important part in bringing the two sexes together, it seems equally 

 clear that by itself, this function is less necessary in Photuris penn- 

 sylvanica than in the various species of Photinus studied by different 

 observers. No exchange of light flashes was made out with certainty 

 in the case of Photuris, and none occurred during copula. The female 

 while shining does not necessarily assume a vertical position, as do 

 Photinus and some of the European species, nor does she curve up 

 the tip of the abdomen as in the latter. In the evening the females 

 were usually resting in a more or less horizontal position, upon some 

 bush or weed, or upon the ground, and the brilliant flash shone ap- 

 preciably through the elytra. The photini were much less active than 



