1890.] ENTOMOLOGICAL NEWS. 3 



Scientific papers, news-notes, reports of societies, etc., are 

 needed from all sources to make this journal just what its name 

 implies, a compend of entomological news. 



Eugene M. Aaron. 



The Evolution of Metallic Colors in Insects. 



BY T. D. A. COCKERELL. 



Metallic coloring in insects cannot be a very recent develop- 

 ment, for we have good evidence that it existed in later Eocene 

 or Miocene times, a Chrysis having been discovered in the Flo- 

 rissant fossil-beds in Colorado. Nevertheless, probably no one 

 would propose that the earliest insects, even of the orders now 

 presenting metallic species in abundance were metallic. There 

 seems to be a graduated series of colors, following in nearly direct 

 sequence, and of these the metallic ones are by no means the 

 first, nor do they occur predominatingly on those parts of the 

 insect which we might suppose least specialized as regards colors. 



For the present we may consider the Coleoptera and Hymen- 

 optera alone, because in color these orders are specially related, 

 and form a section apart from all other insects. The primitive 

 color is probably testaceous, with variations to rufous, orange and 

 yellow. The legs and under parts are often so colored where the 

 upper parts are darker or metallic. Pale legs not unfrequently 

 have dark joints, and this may be related to stimuli due to the 

 motion of the parts. Pimpla conq^iisitor well illustrates the dark- 

 ening about the joints, as well as the difference between the color 

 of legs and ■ body. Sometimes, however, these conditions are 

 reversed, as in Vipio coloradensis, which is a reddish orange species 

 with the legs mainly black. 



From testaceous there is variation to dark brown of various 

 shades — rufous-brown and black. It has been noticed how often 

 phytophagous, and especially wood-eating beetles are brown, and 

 there is good reason to suppose that tannin has influenced their 

 color. Mr. Slater (Ent. Mo. Mag. 1887, p. 72) remarks on the 

 presence of tannin in the tissues of phytophagous beetles, and M. 

 Villon (Atheneum, 1887, p. 787) found tannin in corn-weevils. 

 The non-metallic series of colors, then is something like this : 



