COLEOPTERA. 291 



Mutilla Europsea makes a stridulating noise; and according to 

 Goureau"^ both sexes have this power. He attributes the sound 

 to the friction of the third and preceding abdominal segments, 

 and I find that these surfaces are marked with very fine con- 

 centric ridges; but so is the projecting thoracic collar, into which 

 the head articulates, and this collar, when scratched with the 

 point of a needle, emits the proper sound. It is rather surprising 

 that both sexes should have the power of stridulating, as the 

 male is winged and the female wingless. It is notorious that 

 Bees express certain emotions, as of anger, by the tone of their 

 humming; and according to H. Miiller (p. 80), the males of some 

 species makes a peculiar singing noise whilst pursuing the females. 



Order, Coleoptera (Beetles). — Many beetles are colored so as 

 to resemble the surfaces which they habitually frequent, and 

 they thus escape detection by their enemies. Other species, for 

 instance diamond-beetles, are ornamented with splendid colors, 

 which are often arranged in stripes, spots, crosses, and other 

 elegant patterns. Such colors can hardly serve directly as a 

 protection, except in the case of certain flower-feeding species; 

 but they may serve as a warning or means of recognition, on the 

 same principle as the phosphorescence of the glow-worm. As 

 with beetles the colors of the two sexes are generally alike, we 

 have no evidence that they have been gained through sexual 

 selection; but this is at least posible, for they may have been 

 developed in one sex and then transferred to the other; and 

 this view is even in some degree probable in those groups which 

 possess other well-marked secondary sexual characters. Blind 

 beetles, which cannot of course behold each other's beauty, never, 

 as I hear from Mr. Waterhouse, jun., exhibit bright colors, 

 though they often have polished coats; but the explanation of 

 their obscurity may be that they generally inhabit caves and 

 other obscure stations. 



Some Longicorns, especially certain Prionidse, offer an excep- 

 tion to the rule that the sexes of beetles do not differ in color. 

 Most of these insects are large and splendidly colored. The 

 males in the genus Pyrodes,"" which I saw in Mr. Bates's collec- 



endeavored to show in my 'Origin of Species,' how these sterile be- 

 ings are subjected to the power of natural selection. 



"2 Quoted by Westwood, 'Modern Class, of Insects,' vol. ii. p. 214. 



"^ Pyrodes pulcherrimus, in which the sexes differ conspicuously, 

 has been described by Mr. Bates in 'Transact. Bnt. Soc' 1869, p. 50. I 

 will specify the few other cases in which I have heard of a differ- 

 ence in color between the sexes of beetles. Kirby and Spence ('In- 

 troduct. to Entomology,' vol. iii. p. 301) mention a Cantharis, Meloe, 

 Rhagium, and the Leptura testacea; the male of the latter being tes- 

 taceous, with a black thorax, and the female of u, dull red all over. 

 These two latter beetles belong to the family of Longicorns. Messrs. 



