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 lustrei, is destroyed. 



CHAPTER VII. 



ON LUMINOUS WINGED INSECTS. 



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

 Its Cleanliness — The Pu-pa — The perfect Insect — Difference be- 

 tween the Sexes — The Light — Whether extinguished at pleasure 

 — The luminous Matter — Dartvi?i^!! Opinion — The Effects when 

 placed in Gases — In Acid — Carus^s Opinion — Whether if. con 

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

 ' sus sphcBrocerus — Of the Firefly — Of the Lantemfly — Of tht 

 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." 



