THE ICHNEUMON FLIES. 
295 
When they are full grown, they crawl away from the plant to 
t 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 group 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 little 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, 
