214 OHIO EXPERIMENT STATION: BULLETIN 332 



"The caterpillars just born are pale j^ellow with two rows of 

 black marks along the body, a black head, and with quite sparse 

 hairs. When full-grown they generally appear pale yellowish or 

 greenish, with a broad dusky stripe along the back and a yellow 

 stripe along the sides; they are covered with whitish hairs, which 

 spring from black and orange yellow warts. The caterpillar is, 

 however, very variable both as to depth of coloring and as to mark- 

 ings. Close observations have failed to show that different food 

 produces changes in the coloration; in fact nearly all the various 

 color varieties may be found upon the same tree. The fall genera- 

 tion is, however, on the whole, darker, with browner hairs than the 

 spring generation." 



The cocoon is thin and is spun on or near the surface of the 

 ground. The pupa within is brown. 



Life history. — The winter is passed in the pupal stage and in 

 early June the adults begin to appear. From that time on they 

 appear in straggling numbers, not all at a given time as a well- 

 defined brood as do many insects. There is a time, however, in 

 June and later in the summer when they are more plentiful than at 

 other times. Shortly after emerging the eggs are laid; the cater- 

 pillars soon appear and begin feeding. At the very outset, the 

 silken web, so characteristic of the species, is commenced and soon 

 incloses the leaves upon which the insect is feeding. The web is 

 increased in size as the caterpillars extend their feeding area; and 

 since they are gregarious in their habits, by the time they are full- 

 grown, 2 to 3 feet of the branch may be encompassed by the dirty 

 white web in which is intermingled the castings of the insects as 

 well as the browned remainders of the leaves which have proved too 

 resistant to be used as food. 



Upon the completion of larval growth, the caterpillars leave the 

 web and wander about in search of a place on or just beneath the 

 surface of the soil in which to pupate. The duration of the summer 

 pupal period cannot be more than a few days, whereupon the second 

 brood of adults appears and gives rise to the second generation of 

 larvae. The winter is passed in the pupal stage. 



Nature of work. — The real injury consists, of course, in the 

 destruction of the leaf tissues of the host; and in cases of severe 

 outbreaks, this is no inconsiderable item, as is indicated by a glance 

 at Plate XX, Fig. 3. Occasionally, as the illustration indicates, the 

 host may be almost defoliated, but more frequently just a branch 

 here and there is attacked. In the latter case the actual injury is 

 not so great as is the offense to the eye, particularly when the 



