MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. H 



II.— HINTS OX THE EVOLUTION' OF THE BRISTLES, SPINES, AND TUBERCLES OF NOTODONTIAN 



AND OTHER CATERPILLARS.' 



It is not improbable that, as a rule, all caterpillars at tirst lived on grasse.s, herbaceous and 

 low-j;ro\ving- jilauts generally, and that gradually they began to climb trees, as the latter became 

 developed, and in time became adapted to an arboreal station. As is well known, no deciduous 

 trees or flowering plants ai)peared in such numbers as to form genuine forests before the Cretaceous 

 l)eriod, and about that time in geological history began to appear the kinds of insects which visit 

 flowers and trees that blossom. 



The species of the great lepidopterous family Noctuidie, of which we have in the United States 

 alone over a thousand species, are, as a rule, low feeders. Certain species of Mamestra and of 

 Agrotis, ordinarily feeding on grasses and low herbs, will however, especially early in the spring, 

 ascend trees and shrubs of different kinds and temporarily feed upon the buds; and in summer 

 a species of Mamestra will ascend currant bushes in the night and cut oft' the young, fresh shoots. 



In the group of forms represented by Catocala, Homoptera, and Pheocyma we have true 

 tree inhabiting caterpillars, and, like the Notodontians and dendricolous Geometrids, their bodies 

 difler remarkably from those of the low feeders, being variously spotted and mottled with shades 

 of brown and ash, to assimilate them to the color of the bark of the tree they rest upon, and are, 

 besides, provided with dorsal and lateral humps and warts, to further assnnilate them, in outline 

 as well as in color, to the knots and leaf-scales on the smaller branches and on the twigs among 

 which they feed. And then there is the small group of Noctuo-bomliyees, represented by species 

 of Apatela, Platycerura, Raphia, Charadra, and their allies, which closely "mimic" the hairy, 

 pencileil, or spiny arboreal Bombyces.^ It should, however, be observed that this is scarcely a 

 case of mimicry, but rather of adaptation; the presence of hairs, jtencils, spines, and bristles being 

 ai>parently due to the caterpillars having changed their environment from herbs to trees, and being 

 subjected to the same conditions as the Bombyces themselves.^ 



In the exclusively low feeding cater))illars of certain groups of butterflies the body is usually 

 smooth and adorued with lines and spots, while the general feeders and many arboreal forms are 

 often variously spined and tuberculated, yet many spiued caterpillars of butterflies feed on low 

 herbs.^ The Sphingidic in part feed on low plants and in part on trees, and they do not, except as 

 regards the caudal horn, exemplify our thesis. 



'This section is reprinted with some .alterations from an article in the Proceedings of the Boston Society of 

 Natural History, xxiv, 1890, pp. 482-515, 556-539. 



-Of 34 spt'cies of North America Noctuo-bombyces, whose trausformations are known, all except 1 feed upon 

 trees. (See Edwards's catalojjue. ) 



'It is hardlj' necessary for us to express our entire disagreement with the view of Mr. A. G. Butler, that these 

 Noctuidie are really Xotodoutians, or in any way allied to them. It seems to us that the characters which he uses.to 

 remove them from the Noctuidte are superficial and adaptive. Nearly twenty-five years ago I satisfied myself, after 

 an examination of the denuded head and wings, that the Noctuo-bombyces were true Noctuidiu, and did not depart 

 essentially from the typical genera. 



■•While many, though not all, butterfly larra>, as shown l>y .Scudder and W. H. Edwards, have spine-like gland- 

 ular hairs in the first stage, which may in some cases persist iuto one or two later stages, the body in many species, 

 especially in those which are not general leeilers, but select low-growing, herbaceous jjlants, becomes smooth and 

 ornamented with stripes or spots. However, as a rule, butterfiy larva' can not be divided, as the Bombyces, etc., 

 into high and low feeders; yet from Scudder's "Classified list of food plants of American butterflies" (Psyche, 1889) the 

 following facts and conclusions may be stated : 



Hesperidiy. — Out of 45 species enumerated, all but (3 fee<l on herbs and especially on grasses, and those which 

 feed on tall shrubs or trees, such as Epargyreus titynis and 5 species of Thanaos, stand at the head of the group, which, 

 as everybody knows, is tlie lowest family of butterflies and nearest related to the moths. 



rapilionida: — Of the 6 species enumerated, 3 feed on trees as well as shrubs and herbs; 1 of these, however 

 (/'. ci-espl(iiiites), feeds on trees alone. None of this family are hairy or spined when mature, except P. phih'iwr, with 

 its peculiar flexible, sjiike-like growths. 



Pieriiia: — Of 10 species, all feed on herbs, rarely on low shrubs, and none are armed with hairs, bristles, or 

 spines. The other two groups (Lyc(vnida' and Symphalida.) are general feeders, occurring indifierently on herbs, vines, 

 and trees, except the striking case of the 8 Satyrina-, which feed exclusively on grasses and herbs {E. porUandia, 

 however, sometimes frequenting the Celtis). The very spiny Argyunis larvie feed on Viola. It should also be noted 



