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LETTER XXV. 



ON LUMINOUS INSECTS. 



Wo boast of our candles, our wax -lights, and our Argand lamps, and pity 

 our fellow-men who, ignorant of our methods of producing artificial light, 

 are condemned to pass their nights in darkness. We regard these inven- 

 tions as the results of a great exertion of human intellect, and never con- 

 ceive it possible that other animals are able to avail themselves of modes 

 of illumination equally efficient, and are furnished with the means of guiding 

 their nocturnal evolutions by actual lights, similar in their effect to those 

 which we make use of. Yet many insects are thus provided. Some are 

 forced to content themselves with a single candle, not more vivid than the 

 rushlight which glimmers in the peasant's cottage ; others exhibit two or 

 three, which cast a stronger radiance ; and a few can display a lamp little 

 inferior in brilliancy to some of ours. Not that these insects are actually 

 possessed of candles and lamps. You are aware that I am speaking figura- 

 tively. But Providence has supplied them with an effectual substitute 

 a luminous preparation or secretion, which has all the advantages of our 

 lamps and candles without their inconveniences; which gives light sufficient 

 to direct their motions, while it is incapable of burning; and whose lustre 

 is maintained without needing fresh supplies of oil or the application of the 

 snuffers. 



Of the insects thus singularly provided, the common glow-worm (Lam- 

 pyris noctiluca) is the most familiar instance. Who that has ever enjoyed 

 the luxury of a summer evening's walk in the country, in the southern parts 

 of our island, but has viewed with admiration these " stars of the earth 

 and diamonds of the night ?" And if, living like me in a district where it 

 is rarely met with, the first time you saw this insect chanced to be, as it 

 was in my case, one of those delightful evenings which an English summer 

 seldom yields, when not a breeze disturbs the balmy air, and "every sense 

 is joy," and hundreds of these radiant worms, studding their mossy couch 

 with mild effulgence, were presented to your wondering eye in the course 

 of a quarter of a mile, you could not help associating with the name of 

 glow-worm the most pleasing recollections. No wonder that an insect, 

 which chiefly exhibits itself on occasions so interesting, and whose economy 

 is so remarkable, should have afforded exquisite images and illustrations to 

 those poets who have cultivated Natural History. 



If you take one of these glow-worms home with you for examination, 

 you will find that in shape it somewhat resembles a caterpillar, only that it 

 is much more depressed ; and you will observe that the light proceeds from, 

 a pale-coloured patch that terminates the under side of the abdomen. It 

 is not, however, the larva of an insect, but the perfect fem..'e, 



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