166 NATURAL HISTORY. [CH. IX. 



the latter sucks the gall-nut. When the ichneumon, 

 for the small worm generally turns into that species 

 of fly, comes out, it is often found to be much bigger 

 than the creature it lived on, and here a difficulty 

 presents itself which requires to be explained. How 

 does it happen that the ichneumon worm should be 

 so much bigger than the gall-insect, which is the only 

 substance on which it feeds ? Where does it obtain 

 the additional food required to produce this addi- 

 tional bulk ] Not from the gall-nut, for the ichneu- 

 mon worm does not feed on a vegetable ; and as 

 there is no living thing, save the larva of the gall-fly, 

 enclosed with it in the cell, it must in some way or 

 other obtain it from that. The truth is, that Nature 

 has taught the young of the ichneumon not to kill 

 the larva of the gall-fly outright; it wounds only 

 certain parts which are not vital, and from these it 

 extracts its nourishment. The gall-worm, therefore, 

 goes on sucking the vegetable juice, and elaborating 

 it into animal matter, and as fast as that process is 

 completed, the ichneumon worm abstracts and ap- 

 propriates it ; and so well-timed are the operations 

 of nature, that the moment the ichneumon worm 

 has reached its perfect state, and requires no farther 

 supply of food, the gall-insect, which previously 

 furnished it with this supply, becomes exhausted, 

 and perishes. 



W T hile some persons have supposed that a plant 

 could be converted into a gall-fly, others, and those, 

 too, accustomed to entomological investigation, have 

 mistaken an insect for a gall-nut. Some of our trees 

 appear as if covered with scabs of an oval shape : 

 these remain fixed, show no sign of motion, nor any 

 external mark by which an animal form may be re- 

 cognised ; nevertheless, they are true insects, and the 

 nearer they are to maturity, the less they exhibit 

 the character of animal life, and at the time they are 

 occupied in laying thousands of eggs, they present 

 the aspect of a gall-nut. 



