39 
virtually empty, or that they contain a mass of soft yellow eggs. 
(Fig. 41, e.) 
The insect known as the bag-worm, to which these constructions 
are due, is in several respects one of the most curious in Illinois. 
Altho the parent form is a moth, the female is wingless and naked 
(Fig. 41, c), looking more like a grub than a moth, and the wings 
of the male, instead of being covered with scales, are smooth and 
transparent, somewhat like those of a wasp. (Fig. 41, d.) The 
caterpillar infests a considerable variety of both fruit and shade 
trees, including among the latter evergreens (especially red cedar 
and arbor-vitre, Fig. 42) and several kinds of deciduous trees. 
Fig. 42. Bag-worm, Thyridopteryx ephemerceformis, cases hanging- on arbor-vitae twig. 
(Ohio Experiment Station.) 
It does its injury by eating the leaves of trees, and its numbers are 
often such that they may take virtually every leaf off a tree of 
considerable size. 
The eggs, contained during the winter in the bag-like cases on 
the trees, hatch the following May or June, and the young caterpil- 
lars begin at once to spin for themselves small conical cases (Fig. 
41, g) to which they fasten pieces of leaves from the tree upon 
which they are feeding. As they grow these cases are enlarged 
until they take the form and dimensions already described. The 
caterpillars (Fig. 41, a) travel but slowly, and seldom leave the 
tree upon which they were hatched until they are about full grown, 
