BUTTERFLIES 



The Change to the Chrysalis 



{See plate, pages S2-33.) 



A week or ten days after the last moult of its caterpillar 

 growth the larva commonly becomes full fed and ready to 

 change to the chrysalis state. The details of the way in 

 which this is accomplished vary greatly with different 

 butterflies, as will be noted in the stories of many species 

 later in this book. In general, however, the caterpillar 

 provides a web of silk which it spins against some surface 

 where the chrysalis will be secure and in this web it en- 

 tangles its hind legs. 

 Sometimes there is the 

 additional protection 

 of a loop of silk over 

 the front end of the 

 body. After the legs 

 have become entangled 

 the caterpillar hangs 

 downward until the 

 skin splits open along 

 the median line of the back and gradually shrinks upward 

 until it is almost free, showing as it comes off a curious 

 creature which has some of the characteristic features of a 

 chrysalis. It is seldom at this stage of the same shape 

 as the chrysalis. When the caterpillar's skin is nearly 

 off this chrysalis-like object usually wriggles its body 

 quickly in a manner to entangle a curious set of hooks 

 attached to the upper end in the web of silken thread. 

 This hook-like projection is called the cremaster, and it 

 serves a very important purpose in holding the chrysalis 

 in position. 



Swallowtail Chrysalis, showing (b) the 

 loop of silk over thorax. (After Riley) 



