264 LEPIDOPTERA. 



spot on the tail. These caterpillars alter in color and ap- 

 pearance with each successive moulting, and before they 

 are half grown the projecting points and the white band 

 and spots entirely disappear, the skin becomes perfectly 

 smooth, and of a delicate apple-green color, rather paler 

 at the sides of the body and whitish beneath, and on each 

 segment there is a transverse band consisting of black and 

 yellow spots alternately arranged. When touched, they 

 thrust forth, from a slit in the first segment of the body, 

 just behind the head, a pair of soft orange-colored horns, 

 growing together at the bottom, and somewhat like the letter 

 Y in form. The horns are scent-organs, and give out a 

 strong and disagreeable smell, perceptible at some distance, 

 and seem to be designed to defend the caterpillars from the 

 annoying attacks of flies and ichneumons. These caterpil- 

 lars usually come to their full size between the 10th and 

 20th of July, and then measure about one inch and a half 

 in length. After this they leave off eating, desert the plants, 

 and each one seeks some sheltered spot, such as the side of 

 a building or fence, or the trunk of a tree, where it prepares 

 for its transformation. It first spins a little web or tuft of 

 silk against the surface whereon it is resting, and entangles 

 the hooks of its hindmost feet in it, so as to fix them securely 

 to the spot ; it then proceeds to make a loop or girth of many 

 silken threads bent into the form of the letter U, the ends 

 of which are fastened to the surface on which it rests on 

 each side of the middle of its body ; and under this, when 

 finished, it passes its head, and gradually works the loop 

 over its back, so as to support the body, and prevent it from 

 falling downwards. Though it generally prefers a vertical 

 surface on which to fasten itself in an upright posture, it 

 sometimes selects the under side of a limb or of a project- 

 ing ledge, where it hangs suspended, nearly horizontally, by 

 its feet and the loop. Within twenty-four hours after it has 

 taken its station, the caterpillar casts off its caterpillar-skin 

 and becomes a chrysalis, or pupa, (Plate IV. Fig. 7,) of a 



