36 OUR SHADE TREES AND THEIR INSECT DEFOLIATORS. 
with their old skins, it becomes quite an unpleasant feature in our pub- 
lic thoroughfares and parks. The caterpillars always feed underneath 
these webs; but as soon as they approach maturity, which requires 
about one month, they commence to scatter about, searching for suita- 
ble places in which to spin their cocoons. If very numerous upon the 
same tree the food-supply gives out, and they are forced by hunger to 
leave their sheltering homes before the usual time. 
‘When the young caterpillars are forced to leave their webs they 
do not drop suddenly to the ground, but suspend themselves by a fine 
silken thread, by means of which they easily recover the tree. Grown 
caterpillars, which measure 1.11 inches in length, do not spin such a 
thread. Both old and young ones drop themselves to the ground with- 
out spinning when disturbed or sorely pressed by hunger. 
Pupa and Cocoon.—‘ Favorite recesses selected for pupation are the 
crevices in bark and similar shelters above ground; in some cases even 
the empty cocoons of other moths.* The angles of tree-boxes, the rub- 
bish collected around the base of trees and other like shelter are em- 
ployed for this purpose, while the second brood prefer to bury them- 
selves just under the surface of the ground, provided that the earth be 
soft enough for that purpose. The cocoon itself is thin and almost 
transparent, and is composed of a slight web of silk intermixed with a 
few hairs, or mixed with sand if made in the soil. 
“ The pupa (Fig. 18, d and e) is of a very dark-brown color, smooth 
and polished, and faintly punctate ; it is characterized by a swelling or 
bulging about the middle. It is 0.60 inch long and 0.23 inch broad in 
the middle of its body, or where it bulges a little all round, 
The Moth (Fig. 18, b).—*‘The moths vary greatly, both in size and 
coloration. ‘They have, in consequence of such variation, received 
Fic. 19.—Hyphantria cunea: a-j, wings of a series of moths, showing the variations from the pure 
white form to one profusely dotted with black and brown. 
many names, such as cunea Drury, textor Harr., punctata Fitch, puncta- 
tissima Smith (Fig. 19). But there is no doubt, as proven from frequent 
* We have known the substantial cocoon of Cerura to be used for this purpose. 
