284 NATURAL HISTORY. 



fifty grubs or caterpillars to their nests as food for them- 

 selves and their young. Now, if there were only one 

 million of these birds, of which each one devours 6000 

 caterpillars in the months of April, May, June, and July 

 (by no means a large computation), the number of cat- 

 erpillars and grubs thus destroyed will amount to 

 6,000,000,000 annually." 



482. Caterpillars are all spinners, the thread coming 

 from a fleshy point in the under lip. Besides the em- 

 ployment of this spinning machine in making the cocoon 

 for the pupa state, many of them also use it as a means 

 of escape from their enemies, letting themselves sudden- 

 ly down by the thread they spin to a place of safety. If 

 a bird espies one in a rolled-up leaf, he may not secure it, 

 for, as he puts in his bill at one end, the caterpillar may 

 escape at the other, dropping itself down quickly as far 

 as it pleases. 



483. Most of the caterpillars are solitary in their hab- 

 its, but some live in societies. This is the case with the 

 Tent-caterpillars. These spin large tents of silk in the 

 branches of trees, which are water-proof, although they 

 are so slight in their appearance. They increase very 

 fast, and, if let alone, colonies from the original commu- 

 nity will spread their web-like tents hi all parts of the 

 tree. 



484. Of the caterpillars called Spanworms there are 

 many species. The most conspicuous is what is common- 

 ly called the Canker-worm, so destructive to many fruit 

 and shade trees from devouring their leaves. These cat- 

 erpillars finish their work of devastation in June, when 

 they are only four weeks old, and descend by their silk- 

 en cords to the ground, which they enter to the depth of 

 several inches. Here they pass into the pupa state. In 

 the autumn they issue from the ground in the imago 

 state. The female is wingless, and therefore must climb 

 up the trunk of the tree to lay her eggs on the branches, 

 which she does in clusters of a hundred or more. There 



