THE FALL WEBWORM — SNODGRASS. 



409 



it into the rear end of the cocoon, where henceforth this last evi- 

 dence of its caterpillar origin remains as a shrunken, hairy wad. 

 The pupa sheds the larval skin in one piece, but in all the molts of 

 the caterpillar the hard shell of the head is detached at the neck 

 and cast off separately. 



The pupa is a seedlike object about half an inch in length, having 

 the form and structure shown in figure 10. The head end is rounded, 

 the opposite end tapering; the partly developed legs, wings, and 

 antennae are plainly visible but are stuck down close to the sides and 

 under surface of the body, and are covered all over by a thin coating 

 of varnishlike glaze. At first the pupa is pale and soft and is capable 

 of considerable wriggling movement. The head, thorax and wings 

 are greenish, the abdomen dull yellowish. After about 12 hours, how- 

 ever, the skin hardens to a brittle shell, the colors* change to a uniform 

 dark reddish brown (pi. 2, E), and the power of motion is almost 



Fig. 10. — A, Pupa of webworrn (natural size I inch long) ; 

 B, spines at end of body (more enlarged). 



lost. A hard-shelled pupa like this is called a chrysalis. The three 

 intersegmental lines between the fourth, fifth, sixth, and seventh 

 segments of the abdomen (fig. 9) form deep grooves around the body 

 which retain a flexibility that allows the creature to twist the rear end 

 of the body a little, the only form of exercise it can now take. The 

 fore parts are sculptured all over with small irregular rugosities, but 

 the metathorax and the abdomen are closely punctured with shallow 

 pits, except the sides of the three intersegmental grooves which are 

 smooth and polished. The last segment ends in a flat tongue which 

 bears a fringe of slender spines, each ending in a flat, cupped disk. 



The cocoon-making period of the webworms extends from the 

 middle of July to the second week of August, depending on how early 

 the eggs were laid and hatched in the spring, on the latitude, and on 

 the climate of any particular season. Exact dates for the events of 

 an insect's life are of interest or value only in connection with local 

 conditions and must be determined separately for each locality where 

 the species is studied. After a week or more of confinement in its 

 cell, straight-jacketed in the pupal skin, the creature that was form- 

 erly a web-worm is set free again by nature's invisible warden. The 

 shell-like skin of the pupa opens along two lines, one on the mid line 

 of the back of the first two body segments, the other around the back 

 of the head and down the rear edges of the antennae. The second 



