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LETTER XXV. 



ON LUMINOUS INSECTS. 



We boast of our candles, our wax-ligbts, 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 

 inventions as the results of a great exertion of human intellect, and never 

 conceive 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 rush-light which glimmers in the peasant's cottage ; others 

 exhibit two or three, which cast a stronger radiance ; and a few can dis- 

 play 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 figuratively. 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 burn- 

 ing ; 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 sum- 

 mer 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 illus- 

 trations 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 

 frorn a pale-colored patch that terminates the under side of the abdomen. 

 It is not, however, the larva of an insect, but the perfect female of a 

 winged beetle, from which it is altogether so different that nothing but 

 actual observation could have inferred the fact of their bcins the sexes of 



