Packard.] 
494 
[Feb. 19, 
HINTS ON THE EVOLUTION OF THE BRISTLES, SPINES AND 
TUBERCLES OF CERTAIN CATERPILLARS, APPARENTLY 
RESULTING FROM A CHANGE FROM LOW-FEEDING TO 
ARBOREAL HABITS ; ILLUSTRATED BY THE LIFE- 
HISTORIES OF SOME NOTODONTIANS. 
BY ALPHEUS S. PACKARD. 
It is not improbable that, as a rule, all caterpillars 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 appeared 
in such numbers as to form genuine forests 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 ISToctuidae, 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 off 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 differ re- 
markably 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 as- 
similate 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 by species of Apatela, Platycerura, Raphia, Charadra, 
and their allies, which closely “mimic” the hairy, pencilled, or 
spiny arboreal Bombyces . 1 It should, however, be observed that 
this is scarcely a case of mimicry, but rather of adaptation ; the 
presence of hairs, pencils, spines and bristles being apparently due 
J Of thirty-four species of North American Noctuo-bombyces, whose transformations 
are known, all except one feed upon trees. (See Edwards’ catalogue.) 
