THE ICHjSEUMON FLIES. 295 



When they are full grown, they crawl away from the plant to 

 some retired spot, and there suspend themselves, preparatory to 

 changing into the pupal condition. A few of them succeed in 

 this task, but the greater number never achieve the feat, having 

 been the unwilling nourishers of the ichneumon flies. Just 

 before the larva is about to pass into the pupal state, a number 

 of whitish grubs burst from its sides, and each immediately sets 

 to work at spinning a little yellow, oval cocoon. The walls of « 

 the cocoon are hard and smooth, especially in the interior; but 

 the outside is covered with loose floss-silk, which serves to bind 

 all the cocoons together. Generally, they are very loosely con- 

 nected , but a grcjup of these little objects is now before me, 

 where the cocoons are formed into a flattish oval mass, about the 

 size and shape of a scarlet-runner bean, split longitudinally, and 

 are bound so tightly together, that their shape can barely be 

 distinguished through the enveloping threads. 



As is the case with the cells of the Burnet ichneumon, each 

 cell is furnished with a httle circular door which exactly re- 

 sembles in shape and dimensions the circular pieces of paper 

 that are punched out of the edges of postage-stamps. On the 

 average, about sixty or seventy ichneumon flies are produced 

 from a single cabbage caterpillar. 



The groups of yellow cells are very plentiful towards the 

 middle of summer and the beginning of autumn, and may be 

 found on walls, palings, the trunks of trees, in outhouses, and, 

 in fact, in every place which affords shelter to the caterpillar. 

 Nothing is easier than to procure the insects from the cocoons, 

 as the yellow mass needs only to be put into a box, with a piece 

 of gauze tied over it by way of a cover. Nearly every cocoon 

 will produce its ichneumon, and as the little creatures are not 

 strong-jawed enough to bite through the gauze, they can all be 



secured. 



There are many species of Microgaster; but those which have 

 been mentioned are the most important, and make the most 

 interesting habitations. 



The large oval cocoon was brought from New South Wales, 



