INSECTS. 



275 



excrescences on the discs of the posterior pair." In several Brit- 

 ish butterilies, as shown by Mr. Wonfor, the males alone are in 

 parts clothed with peculiar scales. 



The use of the bright light of the female glow- 

 worm has been subject to much discussion. The 

 male is feebly luminous, as are the larvae and 

 even the eggs. It has been supposed by some 

 authors that the light serves to frighten away 

 enemies, and by others to guide the male to the 

 female. At last, Mr. Belt'= appears to have 

 solved the difficulty: he finds that all the 

 Lampyridae which he has tried are highly dis- 

 tasteful to insectivorous mammals and birds. 

 Hence it is in accordance with Mr. Bates' view, 

 hereafter to be explained, that many insects 

 mimic the Lampyridse closely, in order to be 

 mistaken for them, and thus to escape destruc- 

 tion. He further believes that the luminous 

 species profit by being at once recognized as un- 

 palatable. It is probable that the same explana- 

 tion may be extended to the Blaters, both sexes 

 of which are highly luminous. It is not known 

 why the wings of the female glow-worm have 

 not been developed; but in her present state she 

 closely resembles a larva, and as larvae are so 

 largely preyed on by many animals, we can un- 

 derstand why she has been rendered so much 

 more luminous and conspicuous than the male; 

 and why the larvae themselves are likewise 

 luminous. 



Difference in Size between the Sexes. — ^With 

 insects of all kinds the males are commonly 

 smaller than the females; and this difference 

 can often be detected even in the larval state. 

 So considerable is the difference between the 

 male and female cocoons of the silk-moth (Bom- 

 byx mori), that in Prance they are separated 

 by a particular mode of weighing."'" In the lower classes of the 

 animal kingdom, the greater size of the females seems generally 



Pig. 10. Taphro- 

 deres distortus 

 (much enlarg- 

 ed). Upper fig- 

 u r 8, male: 

 lower figure, 

 female. 



" H. W. Bates, in 'Journal of Proc. Linn. Soc' vol. vi. 1862, p. 7-1. 

 Mr. Wonfor's observations are quoted in 'Popular Science Eeview,' 

 1868, p. 343. 



12 'The Naturalist in Nicaragua,' 1874, pp. 316-320. On the phosphor- 

 escence of the eggs, see 'Annals and Mag. of Nat. Hist.' 1871, Nov., 

 p. 372. 



"Robinet, 'Vers a Sole," 1848, p. 207. 



