92 NATURE SKETCHES IN TEMPERATE AMERICA 



five-eighths of an inch in length. They were warningly colored 

 yellow and striped with reddish brown. The head and legs, 

 together with the last joint, which has two hairy appendages, 

 were intense black. Their bodies were sparingly covered with 

 quite long whitish hairs. When touched, these caterpillars 

 disgorged a yellowish fluid from their mouths, which rnight 

 make them distasteful to birds. 



While I have shown the protection afforded the imago and 

 larva, the eggs of Datana do not share this immunity. They 

 are open to the attacks of parasitic Hymenoptera. The species 

 known as D. interrigima and D. ministra-, we are informed by 

 Girault ^ are destroyed in the egg by the parasites, Telenomus 

 and Eupelmus, respectively. The egg seems to be a vulnerable 

 point of attack which nature has not perfectly protected. It 

 may be, however, that these parasitic Hymenoptera by increas- 

 ing in numbers in one season may limit their own larval food 

 supply. In the next season this would cause a reactive 

 extermination of their own species out of mere lack of the 

 Datana larvae food supply, thus creating a condition of isolation. 



Considering all these facts of the life history of Datana, 

 what a remarkable display of illusive and protective devices 

 seems necessary for its existence ! Romanes ^ says, when there 

 is supplied to us the suggestion of natural selection as a cause 

 presumably adequate to account for this continuous growth 

 in the number, the intricacy, and the perfection of such mechan- 

 isms, that it is only the most unphilosophical mind that can 

 refuse to pause as between the older hypothesis of design and 

 the newer hypothesis of descent. 



'"Psyche," Vol. XIV, 1907, p. 33 

 ^ "Darwin and After Darwin," p. 282. 



