136 OUR INSECT FRIENDS AND FOES 



fore-legs, and climbing up anything that comes in 

 its way. The spot chosen, the insect proceeds 

 to attach a few loose threads to any twig or leaf 

 that may be within its reach, and produces the 

 rough, tangled fibre that is called " refuse silk." 

 When this is accomplished it begins to unwind 

 a long, continuous thread of silk, moving its 

 head from side to side and bending it backwards 

 over its body so that the silk is disposed all 

 round it, forming an oval-shaped cocoon, which, 

 when completed, is about the size of a pigeon's 



egg- 



The silk, when unwound, is 400 feet or more 

 in length, and the remarkable energy displayed 

 by the insect in unwinding this wonderfully 

 long thread is interestingly described by M. 

 Robinet as follows : " The silkworm makes 

 every second a movement extending over about 

 five millimetres. The length of the thread being 

 known it follows that the worm moves its head 

 three hundred thousand times in making its 

 cocoon. If it employs seventy-two hours at its 

 work, it is a hundred thousand movements 

 every twenty-four hours, four thousand one 

 hundred and sixty-six an hour, and sixty-nine a 

 minute, that is to say, a little more than one 

 a second." 



In about four days the cocoon is finished and 

 the silkworm changes to a pupa, remaining in 

 this state from two to three weeks. At the end 

 of this time the skin is ruptured, and the perfect 

 moth is ready to effect its escape from its silken 

 prison. This it does by moistening the cocoon 

 with a liquid contained in a little bladder in its 



