When Darkness has fallen. 113 



Fireflies glow with greatest brilliancy at mid- 

 night. Their luminosity is first seen soon after 

 dark : 



" The glow-worm shows the matin to be near, 

 And 'gins to pale his ineffectual fire." 



As the insects rest on the grass and moss, the 

 difference in the amount of light emitted is quite 

 marked. While the luminous spot indicated 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 bright- 

 ness. The seat of the light of the glow-worm is 

 in the tail, and proceeds from three luminous 

 sacs in the last segment of the abdomen. The 

 male has only two of these, and the light pro- 

 ceeding from them is comparatively small. 

 During favourable weather the light glows 

 steadily, but at other times it is not constant. 

 The fireflies of the tropics those comprising 

 the genus Lampyridce vary to the extent that 

 while certain species control their light, others 

 are without this power. The light of our 

 English glow-worm is undoubtedly under its 

 control, as upon handling the insect it is imme- 

 diately put out. It would seem to take some 

 little muscular effort to produce the luminosity, 

 as one was observed to move continually the 

 last segment of the body so long as it continued 



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