192 INSECTS 



larvas either, for in two or three days they have become 

 full-grown, change to a pupa and then to the adult 

 condition. And so we find that in this, the most highly 

 organized series of insects, scavengers are numerous and 

 effective. So effective, indeed, that their usefulness is 

 not recognized by the average man, because he has no 

 chance of knowing what conditions would otherwise be. 



Among the insects of direct use to man none are of 

 greater importance than the silk-worms. Silk is in 

 such general, almost universal, use, that there is scarcely 

 a moderately well-dressed individual of either sex 

 that does not have some of it as part of a garment 

 or other article of wear. Of the millions who wear or 

 use silk how many ever know, or knowing, realize, that 

 every particle of that silk is the product of a cater- 

 pillar; nothing more than a dried viscid salivary secre- 

 tion, originally intended by nature as a covering to 

 protect the pupal stage of the insect? This covering 

 or case is called a cocoon, and cocoons are spun by 

 many caterpillars, some of them much larger than the 

 Chinese silk- worm. 



Why, then, if there are many silk spinners do we 

 use one only, and what particular advantage has the silk 

 of this species over all others? As to the latter, it has 

 few advantages over other caterpillar silks: it is not 

 nearly so strong as some produced by other varieties, 

 it is not more lustrous, and it is not nearly so great in 

 quantity. Its one great advantage for our use is that 

 it can be more easily reeled than any other known 

 variety. The silk- worm, when ready to make its cocoon, 

 spins a small quantity of loose, supporting threads or 

 floss and then starts inside this framework, spinning 

 with a continuous thread, unless interrupted, until 

 the entire cocoon is completed a thread almost a mile 

 long which, under favorable conditions, can be unwound 



