Chapter XVII. 



Structures of Silk spun by Caterpillars, including the Silk-Worms- 



" Millions of spinning worms, 

 That in their green shops weave the smooth-hair'd silk." 



Milton's Comus. 



All the caterpillars of butterflies, moths, and, in 

 general, of insects with four wings, are capable of 

 spinning silk, of various degrees of fineness and 

 strength, and differing in colour, but usually white, 

 yellow, brown, black, or grey. This is not only of 

 advantage in constructing nests for themselves, and 

 particularly for their pupa?, as we have so frequently 

 exemplified in the preceding pages, but it enables 

 them, the instant they are excluded from the egg, to 

 protect themselves from innumerable accidents, as 

 well as from enemies. If a caterpillar, for instance, 

 be exposed to a gust of wind, and blown off* from its 

 native tree, it lets itself gently down, and breaks its 

 fall, by immediately spinning a cable of silk, along 

 which, also, it can reascend to its former station 

 when the danger is over. In the same way, it fre- 

 quently disappoints a bird that has marked it out for 

 prey, by dropping hurriedly down from a branch, 

 suspended to its never-failing delicate cord. The leaf- 

 rollers, formerly described, have the advantage of 

 other caterpillars in such cases, by being able to 

 move as quickly backwards as forwards; so that 

 when a bird put in its bill at one end of the roll, the 

 insect makes a ready exit at the other^ and drops 

 along its thread as low as it judges convenient. We 



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