164 THIRD ANNUAL REPORT OF 



If this Ursula butterfly were placed side by side with the Archip- 

 pus butterfly, everybody would say at once that no two species could 

 possibly be more unlike in the general style of their coloration. 

 Clearly, therefore, it cannot be considered as in any wise mimicking 

 the latter. Now, the Ursula butterfly is found everywhere through, 

 out the Northern States wherever the Disippus butterfly is met with 

 and yet, while the latter is a common and abundant species, the 

 former is quite rare. This is certainly the case in the Mississippi Val- 

 ley, and will, according to my own experience, and that of others* 

 very generally hold true all over the country. 



To what are we to attribute this fact? It can scarcely be owing 

 to structural differences in the external organization of the two spe- 

 cies; for the two belong to one and the same genus. It surely cannot 

 be because the larvae of the former are more exposed to the attacks 

 of predaceous animals than those of the latter; for they inhabit the 

 same, or very nearly the same trees, and in size, shape and general 

 coloration the two are almost exactly alike. Certainly it can not be 

 because the pupre of one species are more subject to be devoured by 

 birds, insects, etc., than those of the other species ; for it is impossible 

 to tell one pupa from another when placed side by side. The only 

 cause to which we can reasonably attribute the great abundance of 

 the Disippus butterfly and the comparative rarity of the Ursula but- 

 terfly is, that the former mimicks the Archippus butterfly, as has been 

 shown above, and is consequently often mistaken by birds, tree-frogs,. 

 Dragon-flies, Asilus-fiies and other beasts of prey for its unsavory 

 prototype and allowed to escape with impunity, while the latter, hav- 

 ing no such disguise, is ruthlessly devoured by every insect-eating 

 animal that can get hold of it. 



All the facts lead to snch a conclusion. The mimicked species 

 enjoys an almost perfect immunity from the attacks of enemies in all 

 its stages, while the mimicker is persecuted by several. The mim- 

 icker is often found in company with the mimicked, as I have myself, 

 and as others have witnessed. f But what is still more conclusive is 

 the fact observed by Mr. S. H. Scudder* that in the extreme Southern 

 States where the Disippus butterfly occurs, and Archippus is replaced 



* According to Mr. J. A. Lintner, Uisula is "rare" and Disippus is found abundantly in New 

 York. (Proc. Eat. Soc. Phil., III., pp. f>:!-4.) According to Mr. J. Kirkpatrick Ursula is "rather 

 rare" and Disippus "common in the fall" in Ohio. (Ibid., p. 329.) According to Mr. Sain H. 

 Scudder, Ursula is "rather rare" and Disippus is "common" in New England. (Proc. Essex Inst., 

 III., p. 165.) According to Mr. Billings, who does not seem to have met with any Ursula at all, 

 Disippus is ''very common from July to October" in Canada West. (Lanad. En torn., I., p. 45.) 

 There appear to be some exceptions to this rule, however, for Mr. Thos. VV Higginson, of Mew- 

 port, R. I., declares (Am. Entomologist, II., p. 177.) that Ursula is one of the commonest of the 

 large butterflies there and decidedly more so than Disippus. I was also informed while at Troy 

 last fall, that the former outnumbered the latter in the vicinity of New York City in the year 1863, 

 though the previous years it had been quite rare. These exceptions to the rule may be owing to- 

 one cause or another, but I shall attempt to explain them when I come to consider the objections 

 to the theory which I espouse. 



t .Mrs. Mary Treat, of Vineland, N. J., writes that Archippus was unusually abundant there last 

 fall, and that she found Disippus in company with it. 



t Nature, Vol. Ill, p. 147. 



