GROWTH AND TRANSFORMATIONS OF INSECTS 65 



they eat more of the leaf sub- 

 stance, devouring all but the 

 midrib and veins when half 

 grown, and, when larger, leave 

 only the midrib. The carpet- 

 like web which they spin also 

 becomes more evident as they 

 grow older, often binding to- 

 gether the ends of near-by twigs, 

 especially where the caterpillars 

 rest after feeding. The full- 

 grown caterpillar is about two 

 inches long, with numerous 

 branched black spines. It is 

 blackish in color, with a row 

 of red spots down the back, 

 and with transverse rows of 



FIG. 84. Twigs denuded by spiny elm cater- minute white Spots. 



pillars, bearing their cast skins. (Reduced) 



chrysalis. The 



caterpillars are full grown in 



(Photograph by Weed) 



about four weeks. Dr. Weed, in his interesting account of this spe- 

 cies, describes its transformation as follows : 



They then leave the tree or shrub on which 

 they have been feeding, and scatter about, seeking 

 some sheltered situation. Having found this, 

 perhaps beneath a stump or along the underside 

 of a fence, each caterpillar spins a web of silk 

 along the surface. It then entangles the hooked 

 claws of its hind legs (anal prolegs) in this silken 

 web and lets its body hang vertically with the head 

 end curved upward. It remains in this position 

 for some hours before the skin along the back just 

 behind the head splits apart, and is gradually 

 wriggled upward until it is finally all removed, 

 and there hangs in place of the caterpillar a 

 peculiar object having no definite form that of 

 the chrysalis}- 



In this quiet chrysalis the insect is apparently f IG ' 8 5* Mourning cloak 



butterfly emerging from 

 chrysalis 



(Photograph by Weed) 



almost as inert as a mummy. If you touch it, it 

 i See Fig. 83. 



