132 NETTLE TORTOISE-SHELL BUTTERFLY. 
glutinous substance, by means of which they adhere 
firmly to the plants on which they are deposited. 
About the middle of May, the young caterpillars 
emerge from this envelope, and may be observed, of 
a light green colour, congregated and moving about 
on the tops of the nettles, under a web of exquisitely 
fine fibres, which covers the whole tops of the plant, 
and is taken for a spider’s web—to which it has a 
strong resemblance—by those unacquainted with the 
history of insects. It is not long before they cast 
their first skin, at which time they shift to a fresh 
part of the plant, and leave behind them their old 
covering, adhering to the web. On acquiring their 
third skin, they again change place, but still keep 
under the protection of their web. In this change 
they become black ; after which they quickly in- 
crease in bulk, and are soon so large, that the com- 
munityare forced to separate into distinct companies. 
They undergo, altogether, six changes of skin while 
in the caterpillar state, in the last of which they 
become solitary, living a retired life, quite remote 
from each other ; and, in this condition, they make 
such ravages among the nettles, that nothing re- 
mains on the plants to which they attach themselves 
but the fibres of the leaves and stalks. These cater- 
pillars are frequently so numerous, and so thickly 
studded on the plants, as to give them the appear- 
ance of being covered with black velvet. 
The larvee of the Nettle Tortoise-shell Butterfly 
