408 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



cocoons of other species. The cocoons of tussock moths are generally 

 sticking about in handy places on the trees and fences, and in one 

 of these still inhabited by the tussock pupa the writer once found 

 a webworm stretched out beside the proper occupant, apparently 

 waiting for its own change to take place. When the webworm's 

 eocoonis complete it is a grayish brown, fuzzy, flimsy, oval structure, 

 about five-eighths of an inch in length (pi. 2, D), and is often cov- 

 ered all over with grains of sand or bits of other surrounding mate- 

 rial. Its walls are thin, but there is no opening left for the escape 

 of the future moth, which must provide its own exit. 



The caterpillar within the cocoon is a homely object that may 

 well be glad of its concealment from the public. Shorn of its long 

 hairs and shrunken to three-fourths its earlier length it now looks 

 like nothing but a wretched worm, and bears little resemblance to 

 the proud creature so finely dressed that but lately scorned all 

 restraint as it wandered at large in joyous freedom. When the cat- 

 erpillar's work is done it falls into a state of torpor, becoming slug- 

 gish and inert, though it is still irritable and recoils from any touch, 

 even from any tickling on the ends of what hairs it has left ; but it 

 exhibits nothing of that active resentment to disturbance so charac- 

 teristic of its active life. The small size of the cocoon compels it 

 to lie in what looks like a most uncomfortable position with the 

 head and tail ends bent beneath the under surface of the body. 

 When a caterpillar in this condition is liberated from the cocoon 

 it continues in its stupor for a few minutes and then appears to 

 awake and become conscious that it is free again. It now slowly 

 unbends, stretches, squirms, rolls over and finally, extending itself 

 to nearly its normal length, Avalks off, gaining agility with exer- 

 cise. The instinct to weave even becomes active again and some 

 individuals are able to make what might pass for a second cocoon, 

 though many can spin only a few threads, the one cocoon appar- 

 ently having exhausted their supply of silk. But a caterpillar that 

 is too far gone in the prepupal sleep is capable of little action beyond 

 an occasional squirm or a sidewise roll. Such as this will soon 

 change to the pupa wherever it may be lying. 



The writer can not say just how long the webworm caterpillar 

 remains in its dormant state, but most species spend about 24 hours 

 in what is called the pre-pupal period. Then the skin splits over 

 the back of the head and thorax and a hard-shelled object appears 

 within. This is the pupa, which has already formed inside the 

 larval skin. It has no free appendages, but by a wriggling and 

 squirming of its flexible body it pushes its head and shoulders out 

 of the rent, works the loosened skin down over its body, finally push- 

 ing it off completely from its tapering terminal segments and crowds 



