How Animals Work. 



moves its head backwards and forwards, a veritable 

 living shuttle weaving a golden canopy, until at last 

 the walls of the cocoon grow so thick that it is quite 

 hidden from sight. For four days does this inde- 

 fatigable weaver labour at the spinning of its cocoon, 

 and by the time it is finished it has been calculated 

 that the Silkworm has moved its head backwards and 

 forwards three thousand times, and unwound a thread 

 about one thousand metres in length. The labour 

 expended upon the construction of the cocoon, and the 

 amount of material secreted by the silk-producing 

 organs of the caterpillar, seem truly prodigious when 

 we consider the comparatively small size of the insect ; 

 indeed, it has been estimated that forty thousand cocoons 

 would suffice to surround the earth at the Equator 

 with a single silken thread. 



Though the Silkworm is the greatest weaver of 

 them all, there are many caterpillars that display con- 

 siderable ingenuity in the construction of their cocoons, 

 using various building materials in addition to their 

 silk secretion. The caterpillar of the Sycamore Moth 

 (Acronycta aceris), which is covered with tufts of yellow 

 hair, first spins an outer wall of pure silk to its cocoon, 

 and when this is thick enough, proceeds to tear out its 

 hair, according to Reaumur, in the following manner, to 

 form a lining : " Its two jaws are the pincers the 

 caterpillar uses in seizing a portion of one or other of 

 the tufts of hair ; and when it has seized it, it tears it 

 out without much difficulty. It at once places this 

 against the tissue it has already commenced, in which 

 it entangles it at first simply by pressure ; it fixes it 

 then more securely by spinning over it. It does not 



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