348 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
loosened epidermis, forming tentiform mines, or they make a shelter 
by folding over a part of the leaf. Those in the genera Cameraria and 
Pha yllonore ycter feed continuously in the mines and pupate there. 
The families Gelechiidae, Heliozelidae, Olethreutidae, Yponomeuti- 
dae, and Tortricidae each include species with leaf-mining habits, and 
some of these species are important pests of evergreens. 
There are some 18 families of Lepidoptera represented among the 
leaf miners, but the 10 noted above include most of the species of 
economic importance. Their identification is often difficult, and the 
name of the host plant, the form and color of the mine, the frass, the 
sulk, the larva, the pupa, and the molt skins, particularly the head 
capsules, are used in the specific determination of these insects. 
The skeletonizers, as the name implies, eat the parenchyma of the 
leaves, usually leaving only the tougher veins and midribs. This com- 
mon name applies to species of Bucculatriz, and is also used for such 
species as Anthophila pariana Clerck, and others. 
The bagworms and casebearers include species the larvae of which 
construct and inhabit portable baglike structures, or cases, such as 
members of the families Psy chidae, Coleophoridae, and Lacosomidae. 
The leaf rollers or leaf tiers conceal themselves in leaves folded, 
or rolled, or fastened by silk. Species having these habits are found 
in the famihes Tortricidae, Gelechidae, Pyraustidae, Pyralididae, 
Oecophoridae, Hesperiidae, and others. In general, the species are 
solitary in habit. 
The webworms or tentmakers for the most part are gregarious, and 
either spin silk over several leaves to form a web, or spin a silken tent 
in a crotch of a tree or shrub. Some species feed within the web, 
enlarging it so as to enclose more foliage when necessary, and other 
species leave the tent to feed but return for their resting periods. 
These habits are found among species of the families Tortricidae, 
Epipaschiidae, Lasiocampidae, Arctiidae, and others. 
The larvae that live mostly in the open without larval cases or webs 
for protection are called free feeders. Certain structural characters 
and the vestiture, as well as the habits, permit the division of these 
larvae into many groups that will aid in identifying them. 
The sluglike larvae include the “puss” caterpillars, or “possum- 
bugs,” of the family Megalopygidae and the slug and saddle-back 
larvae of the family Limacodidae. 
The hairy caterpillars of the free feeders include the “woolly-bears” 
of the Arctiidae, which are densely clothed with clusters of hairs 
arising from tubercles. The “tussocks” of the family Lymantridae 
have conspicuous tufts of hairs on the backs of some of the segments, 
and long pencils of hairs at each end of the body; the “Datanas” of 
the family Notodontidae are gregarious and have a peculiar habit of 
clinging to the twigs or foliage with their middle prolegs and holding 
the head and anal end of the body i in a more or less perpendicular posi- 
tion. Some species of the genus Acronicta, family Phalaenidae, are 
densely clothed with hairs. 
The spiny caterpillars include species of the family Nymphalidae 
and some of the Saturniidae, Citheroniidae, and others. These are 
heavily armed with coarse branched or barbed spines. 
The giant silkworms of the family Saturniidae are more or less 
armed with tubercles and spines and are conspicuous because of their 
large size. The larvae of Citheroniidae are also armed with spines or 
