THE FALL WEBWORM SNODGRASS. 



399 



pillars always lag behind, but these will eventually follow the others 



through the series of deserted tents. 

 At the end of a 



week of feeding and 



working the cater- 

 pillars a 1 1 a in a 



length of about one- 

 twelfth of an inch ; 



the largest ma}' be 



a trifle longer than 



this. The color of 



the body is pale 



greenish yellow, the 



head is black in 



strong contrast, on 



the back of the first 



segment there is a 



prominent dark 



Brown, shield-like, 



plate, and on the last 



segment a smaller, 



paler one (fig. 5). 



The body is sparsely 



covered with long 



hairs placed singly 



on small brown 



knobs that give the skin a speckled appearance. The arrangement of 



these knobs, called tubercles, is sufficiently shown by the figure. The 

 I , / / / hairs on the back are 



specially long and the 

 two median rows are 

 very black. Caterpil- 

 lars with these char- 

 acters are still in the 

 first period of their 

 lives, which we will 

 call Stage I. Ento- 

 mologists use the word instar to designate the insect inself in any 



stage. 

 After the first week some of the caterpillars will be observed to 



have changed in appearance and to have become abruptly larger. 



A search through the tents will reveal many little hairy wads which 



are dry, empty caterpillar skins. This means that the first molt 



has begun and that the caterpillars are entering Stage II. Those 



that have molted are about one-sixth of an inch long, twice the 



Fie. 4. — First extension of the web to neighboring twigs 



and leaves. 



Kig. 



-Youns 



webworm in Stage, I (natural length 

 A Inch.) 



