314 INSECT ARCHITECTURE. 



on the twenty-second and twenty-third days. The 

 fifth age, in such cases, lasts ten days, at the end of 

 which, or thirty-two days after hatching, the cater- 

 pillars attain their full growth, and ought to be three 

 inches in length ; but if they have not been properly 

 fed, they will not be so long. 



With the age of the caterpillar, its appetite in- 

 creases, and is at its maximum after the fourth moult- 

 ing, when it also attains its greatest size. The silk 

 gum is then elaborated in the reservoirs, while the 

 caterpillar ceases to eat, and soon diminishes again 

 in size and weight. This usually requires a period 

 of nine or ten days, commencing from the fourth 

 moulting, after which it begins to spin its shroud of 

 silk. In this operation it proceeds with the greatest 

 caution, looking carefully for a spot in which it may 

 be most secure from interruption. 



" We usually," says the Abbe de la Pluche, " give 

 it some little stalks of broom, heath, or a piece of 

 paper rolled up, into which it retires, and begins to 

 move its head to different places, in order to fasten 

 its thread on every side. All this work, though it 

 looks to a bystander like confusion, is not without 

 design. The caterpillar neither arranges its threads 

 nor disposes one over another, but contents itself 

 with distending a sort of cotton or floss to keep off 

 the rain ; for Nature having ordained silk-worms to 

 work under trees, they never change their method, 

 even when they are reared in our houses. 



" When my curiosity led me to know how they 

 spun and placed their beautiful silk, I took one of 

 them, and frequently removed the floss with which it 

 first attempted to make itself a covering ; and as by 

 this means I weakened it exceedingly, when it at last 

 became tired of beginning anew, it fastened its threads 

 on the first thing it encountered, and began to spin 

 very regularly in my presence, bending its head up 



