June, 1908. J THE VICTORIAN NATURALIST. 29 



During flight the flashes will recur at intervals of a second or two, 

 with very little light, or even none, in between. Occasionally no 

 light at all will be emitted for a few seconds. Such, in general, 

 is the normal occurrence of the light when the insect is not inter- 

 fered with in any way. 



When a firefly is touched by a stick or one's finger the flashes 

 become more brilliant, and recur more rapidly than usual, while 

 the interval between flashes is filled by a stronger light than is 

 generally to be seen. As the beetle flies through the air after 

 being touched in this way it gives out a continuous stream of light, 

 punctuated by quickly recurring brilliant flashes. On attempting 

 to capture a firefly which is not flashing rapidly or brilliantly, 

 failure is often turned into success by the fact that the emission 

 of light increases by interference with the freedom of the insect, 

 thus enabling one to follow easily the course of the fugitive. 

 When one imprisons a firefly in a glass tube, flasli will follow flash 

 in quick succession for some ten or fifteen minutes after, the 

 firefly meanwhile being busily engaged in trying to escape from 

 the tube. Without difficulty, ordinary handwriting in a letter can 

 be read by the light from three or four of such captives. After 

 some time, when the beetle becomes less excitable, and apparently 

 realizes the futility of its endeavours to escape, it will emit very 

 little light, only occasionally giving a feeble flash. On the firefly 

 being released from captivity, the light will again increase in 

 brightness, only to decrease again on the re-imprisonment of the 

 agent. 



A close examination of the Firefly Beetle shows that the light is 

 emitted from the ventral surface of the two posterior segments of 

 the abdomen. When the flash begins a small circular patch on 

 the last segment glows more and more brightly. Immediately 

 after the beginning of this flash, and while it is becoming more 

 intense, a circular patch on the middle of the second last segment 

 glows, followed by a lighting up of two lateral circular patches. 

 These three areas of light increase in size until they fuse into one 

 another. Then from the whole of the ventral surface of the two 

 posterior segments of the abdomen an emission of extremely 

 bright and beautiful glowing light occurs. The light dies away 

 from both segments simultaneously. When a firefly dies slowly, 

 the light becomes less and less distinct, failing utterly at death. 

 The sudden death of the insect will cause an abrupt cessation of 

 the light. 



The foregoing observations seem to me to lead distinctly to 

 the conclusion that the glowing of the firefly larva, and the 

 brilliant flashes alternating with dull light emitted by the imago, 

 are not due to the presence of phosphorescent material in or on 

 the body of the beetle, but rather to a nervous e.xcitation or 

 impulse, caused, to some extent, by influences from outside 



