CH. VII.] LUMINOUS WINGED INSECTS. 117 



spider-bags only bears the weight of thirty-six 

 grains, while that of the common silkworm is ca- 

 pable of bearing two drachms and a half, although 

 the former is about eighteen times thicker ; and that 

 they furnish much less silk than the silkworms, as 

 the weight of the spider-bag is about a grain, and 

 when clean for use it loses two thirds, while that 

 of the silkworm weighs four grains. Therefore it 

 requires 2,304 of the latter to produce a pound of 

 silk, while it takes at least 27,648 spiders to pro- 

 duce the same weight ; the work of twelve spiders 

 only equals that of one silkworm; nor can the 

 thread be wound off as easily as that of the silk- 

 worm, but must, of necessity, be carded ; by which 

 means, being torn in pieces, its evenness, which 

 contributes much to its lustre, is destroyed. 



CHAPTER VII. 



ON LUMINOUS WINGED INSECTS. 



History of the Glow-worm Description of the Egg The Larva 

 Its Cleanliness The Pupa The perfect Insect Difference be- 

 tween the Sexes The Light Whether extinguished at pleasure 

 The luminous Matter Darwin's Opinion The Effects when 

 placed in Gases In Acid C arm's Opinion Whether it con 

 tain Heat Murray's Opinion History of the Lantern of Paus 

 sus sphoerocerusOf the Firefly Of the Lantemfly Of the 

 Candlefly Object of the Light. 



WE propose in this chapter to give an account of 

 those insects which are remarkable for their lumi- 

 nous property. Most of our readers may have ob- 

 served a phenomenon, which is thus described by 

 the poet Thomson, 



" Among the choked lanes, on every hedge 

 The glow-worm lights his gems ; and through the dark 

 A moving radiance twinkles." 



