98 SOCIAL HABITATIONS. 
leaf. In process of time, they burst from the egg-shell, 
and commence their business of eating, which is carried on 
without cessation throughout the whole time of the larval 
existence, with a few short intervals, while they change 
their skins, 
When they are full grown, they crawl away from the 
plant to some retired spot, and there suspend them- 
selves, 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 unwill- 
ing 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 connected; 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 resembles 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 sammer 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 
