MEJMOIKS OF THE jS^ATIO^^AL ACADEMY OF SCIE^ICES. 
11 
II.— HINTS ON THE EVOLUTION OF THE BRISTLES, SPINES, AND TUBERCLES OF NOTODONTIAN 
AND OTHER CATERPILLARS.' 
It is not improbable that, as a rule, all caterpillarvS at first lived on grasses, herbaceous and 
low-growing plants 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 aj^peared in such numbers as to form genuine foi'ests before the Cretaceous 
period, 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 !N'octnid:e, 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 Nlamestra will ascend currant bushes in the night and cut off the young, fresh shoots. 
In the group of forms represented by Catocala, Homoptera, and Pheocyina we have true 
tree inhabiting caterpillars, and, like the Notodontiaus and dendricolous Geometrids, their bodies 
differ 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 assimilate 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-bombyces, represented hy species 
of Apatela, Platycerura, Raphia, Charadra, and their allies, which closely ‘‘mimic” the hairy, 
lieuciled, or spiny arboreal Bombyces.^ It should, however, be observed that this is scarcely a 
case of mimicry, but rather of adaptation; the iiresence of hairs, pencils, spines, and bristles being 
apparently 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 caterpillars of certain groups of butterflies the body is usually 
smooth and adorned with lines and spots, while the general feeders and many arboreal forms are 
often variously spiued and tuberculated, yet many S])ined caterpillars of butterflies feed on low 
herbs.-* The Sphingidm 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, xxir, 1890, pp. 482-515, 556-559. 
2 Of 34 species of North America Noctiio-homhyces, whose transformations are known, all except 1 feed uimn 
trees. (See Edwards's catalogue.) 
®It is hardly necessary for ns to express onr entire disagreement with the view of Mr. A. G. Butler, that these 
Noctuidic are really Notodontians, or in any way allied to tliem. It seems to ns that the characters w’hich lie uses.to 
remove them from the Noctnidm are superficial and adaptive. Nearly twenty-five years ago 1 satisfied myself, after 
an examination of the denuded head and wings, that the Noctuo-bombycos were true Noctuidie, and did not depart 
essentially from the tyincal genera. 
■‘While many, tliougU not all, butterfly larvfp, as shown by Scudder and W. H. Edwards, have spine-like gland- 
ular hairs in the flrst stage, which may in some cases persist into one or two later stages, the body in many species, 
especially in those which are not general feeders, but select low-growing, herbaceous plants, becomes smooth and 
ornamented with stripes or spots. However, as a rule, butterfly larva* can not be divided, as the Bombyces, etc., 
into high and low feeders; yet from Scudder’s “Classiliedlist of food plants of American butterflies'' (Psycho, 1889) the 
following facts and conclusions may be stated: 
I/esperida'. — Out of 45 species enumerated, all but 6 feed on lierba and especially on grasses, and those which 
feed on tall shrubs or trees, such as J^pargyreus lityrus and 5 species of Thanaos, stand at the head of the group, which, 
as everybody knows, is the lowest family of butterflies and nearest related to the moths. 
rajnUonida’. — Of the 6 species enuiueratod, 3 feed ou trees as well as shrnbs and herbs; 1 of these, however 
(P. cresjihontefi), feeds ou trees alone. None of this family are hairy or spined when mature, except P. philenor, wdth 
its peculiar flexible, spike- like growths. 
Pierina:. — Of 10 species, all feed on herbs, rarely ou low shrubs, and none arc armed with hairs, bristles, or 
• spines. The other two groups {LycwnUlw and Xyinphalidw) are general feeders, occurring indifferently on herbs, vines, 
and trees, except the striking case of the 8 Satyrinie, which feed exclusively on grasses and herbs (E. ^yortlandia, 
however, sometimes freipieuting the Celtis). The very spiny Argyunis larvcc feed ou Viola. It should also be noted 
