78 



THE FOREST TENT CATERPILLAR 



Wherever they go these little larvie spin a silken thread which 

 marks their pathway, although the thread is so slender that it 

 is generally to be seen only through a lens. 



The tiny caterpillars feed upon the tender leaves of the twig 

 near where the egg mass was placed. In about two weeks 

 each larva increases in size to such an extent that the skin in 

 which it came from the egg is too small for it. This skin then 

 splits open along the back, and the caterpillar crawls out clad 

 in a new skin that had gradually been forming beneath the old 

 one. This skin-shedding process is called moulting ; it is the 

 general way in which insects provide for increase in size. All 

 sorts of caterpillars as well as other insects moult as they grow. 

 After the first moult the Forest Caterpillars begin feeding 

 again, eating of course more and more of the foliage as they 

 become larger. A week or so later they again moult, a pro- 

 cess which is twice repeated thereafter at similar intervals. 

 At tlie period of moulting the caterpillars are in the habit of 

 congregating upon the trunks or larger limbs of the tree, often 

 not far from the ground. Beneath the mass of larvae there is 

 an inconspicuous web in which the feet are more or less en- 

 tangled. The appearance of the caterpillars at such times is 

 well shown in the photograph reproduced in Fig. 24, for the 

 use of which I am indebted to Dr. F. W. Russell, Winchen- 

 don. Massachusetts. 



When the caterpillars become full grown in this, their larval 



state, each seeks a place 

 in which to spin its co- 

 coon. Many remain in 

 the trees and tie up the 

 leaves by silken threads, 

 thus forming a partial 

 or complete covering for 

 the cocoon (Fig. 29). 

 Others seek crevices in 

 the rough bark, while 

 many others — probably 

 one-half or more of all 

 the caterpillars — forsake 

 the tree and wander oft 



a 



Fig. 22. Forest Tent C aterpillar ; a, markings 

 on one ring of the back ; /', markings on 

 one ring of the side. 



