32 HOW TO OBSERVE INSECTS. 



As its body increases in size, its skin, unable to stretch much, 

 becomes too small and the larva is obliged to shed it. As the 

 time to molt approaches, the larva spins a carpet of silk on the 

 leaf to give it a firai foot-hold and then becomes quiet. Its in- 

 action is occasionlly interrupted by struggles intended to loosen 

 from its body the skin it is about to cast. Finally the skin bursts 

 open on the back and the inse'ct struggles free from it. After 

 making a meal off the cast skin it remains quiet for a time to give 

 the new skin a chance to harden. It then begins to eat and grow 

 until it is time for it to molt again. When it has grown to its full 

 size, of about one and one half inches in length, it usually leaves 

 the cabbage and seeks the underside of a board, fence rail, or 

 other convenient object. 



If observations are being carried on in the school-room, the 

 plant on which the larvae are feeding should be placed in a box 

 with its front closed by mosquito netting before they have reached 

 taeir full size; otherwise they are liable to wand.er so far as to be 

 lost. 



Having found an object from the underside of which it can sus- 

 pend itself, it spins a band of silken threads crosswise under its 

 back, attaching the band at each end to the object it is resting be- 

 neath. Figure 34. A 

 silken pad is also spun 

 at its tail end. It then 

 sheds its skin in some- 

 what the same manner 

 that has been described 



for its ordinary molts, 



, e , Figure 34.. 



but instead of simply a 



,, Pupa of cabbage butterfly, afier Scuddar. 



large larva coming forth, 



there appears a smooth, shiny object, without any external appen- 

 dages, known as a pupa. During the process of shedding its 

 larval skin, the tail end of the pupa is firmly attached to the silken 

 pad already mentioned, and the silken loop extending crosswise 

 under its back like a hammock suspends it with sufficient security. 



The pupa is incapable of any movement beyond a slight twitch- 

 ing when disturbed. The general color of the pupa is usually 

 light gray but it varies often to yellowish green; numerous brown- 

 ish dots are scattared over its surface. 



The pupa state lasts, in summer, for from ten to twelve days. 

 Its transparency is then seen to change somewhat, and soon after 

 the skin bursts open on the back, and the adult butterfly, known 



