THE CANADIAN ENTOMOLOGIST. 357 



A NOTE ON THE LIGHT-EMISSION OF SOME AMERICAN 



LAMPYRID/E. 



BY F. ALEX. MC DERMOTT, WASHINGTON, D. C. 



In connection with the collection of specimens for some work on 

 physiologic light, I have had occasion to observe the modes of light- 

 emission of some species of American Lampyridfe common in this neigh- 

 bourhood (Washington, D. C.), and thought that some of these might be 

 of interest. The species most common here, at least within the city limits, 

 is Photiiius pyralis Linn.; Photinus consajigiimeus Lee, Photitms scintil- 

 lans Say, Photuris penntylvatiica Geer, and Lecontea ( Pyractomena) 

 angulata Say, were also observed. Each of these species appears to emit 

 its light in a different and characteristic way — sometimes in several ways. 



The insect whose light-emission is best known here is the Photinus 

 pyralis. This is the insect which abounds in our parks during the sum- 

 mer, and with whose peculiar "dipping" flight as it flashes most of us 

 Washingtonians are familiar. This dipping flight is indulged in by the 

 male, apparently while seeking its mate, and consists usually of a short 

 downward flight, followed by a longer upward flight, during the whole of 

 which the insect emits a continuous light, the whole phenomenon occupy- 

 ing from half a second to a second. The light appears to be at its 

 maximum brilliancy during the turn at the lowest point of the flight, 

 increasing rapidly on the descending flight, and decreasing on the ascend- 

 ing. At the completion of the flash the insect remains dark for some 

 seconds, or perhaps minutes, and then repeats the operation, either near 

 the same locality, or after a flight to some point usually not far from its 

 starting point. Sometimes the light does not entirely die out immediately 

 after the flash, but a phosphorescent glow is left shining for some seconds, 

 sometimes till the next flash — and by this residual glow the insect may be 

 trailed with ease at night. Later in the evening the insects fly higher, 

 and then flash when flying straight, or, indeed, in any direction ; the 

 dipping flight appears to be indulged in only when near the earth. Occa- 

 sionally they flash near the earth when flying in a curve the reverse of 

 that described, that is, a rising flight followed by a descending one ; rarely, 

 also, they may be observed to twinkle, as will be described for the Photuris. 



This description applies only to the male pyralis. The luminous 

 organ of the male of this species occupies the entire ventral surface of the 

 two abdominal segments next to the last, as well as a good portion, almost 

 half, of the preceding segment. The luminous organ of the female 

 occupies only a small spot, about a third of the ventral area, of the third 



November, 1910 



