186 NATURAL HISTORY. [CH. X. 



After having eaten its fill, in its appointed time it 

 seeks the hollow of a leaf, glues itself to it, and con- 

 tracting its body into an oval, undergoes that species 

 of metamorphosis in which the insect retracts itself 

 within its own skin, which, becoming hard, forms a 

 cocoon, and ultimately appears in its perfect form 

 of a fly. 



Another enemy of the aphis is an insect, called by 

 Reaumur the lion of the aphides (hemerobius). 

 " We sow grain," says he, " in our land, for the pur- 

 pose of providing ourselves with food. It appears 

 that nature rears aphides on plants for the purpose 

 of feeding other species of insects, which, without 

 them, would perish of hunger." 



The following figure is a larva of the lion of the 



aphides; a title which it well deserves from its vo- 

 racity. The largest plant-louse is sucked by it in a 

 few moments ; and, like its prototype, it is not inac- 

 tive, but hunts for its prey. They do not spare even 

 each other ; for, if by chance one of its own species 

 should be found between its suckers, it makes not 



