290 NATURE AND WOODCRAFT. 



somewhat curious confirmation of this is the fact 

 that in the insect genus to which our British 

 fire-flies belong — the Lampyrida3 — the degree 

 of luminosity is in inverse proportion to the 

 development of the vision. 



Fire-flies glow with greatest brilliancy at 

 midnight. Their luminosity is first seen soon 

 after dark. " The glow-worm shows the matin 

 to be near, and 'gins to pale his effectual fire." 



As the insects rest on the grass and moss, 

 the difference in the amount of light emitted is 

 most marked. While the luminous spot in- 

 dicated by a female is quite bright, the males 

 show only as the palest fire. When on the 

 wing the light of the latter is not seen at all. 

 Heavy rain, so long as it is warm, serves only 

 to increase the brightness. The seat of light in 

 the glow-worm is in the tail, and proceeds from 

 three luminous sacs in the last segments of the 

 abdomen. The male has only two of these sacs, 

 and the light proceeding from them is compara- 

 tively small. During favourable weather the 

 light glows steadily, but at other times it is not 

 constant. The fire-flies of the tropics — even 

 those comprising the genus Lampyridse — vary 

 to the extent that while certain species control 



