150 THE INSECT WORLD. 
presents, we must consider the problem which the caterpillar has 
to solve. In this problem there are two unknown quantities to 
be discovered. For the first, the caterpillar must suspend itself 
firmly ; for the second, the pupa, having no communication with 
the object which supports it, must be suspended in the same 
manner. This problem is difficult, apparently impossible, to solve. 
It is only by watching these insects at work that one can discover 
the admirable mysteries of their lives. Swammerdam, Valisnieri, 
and other observers who have studied insects, had not, however, 
observed the manceuvres of caterpillars in this curious phase of 

Figs. 102, 103.—Caterpillars of the small Tortoise-shell Butterfly (Vanessa urtice) 
undergoing their metamorphosis. 
their existence. It is to Réaumur, again, that science is indebted. 
for the most charming and valuable observations on this point. 
He got together a great number of caterpillars of the small 
Tortoise-shell Butterfly (Vanessa urtice), black, prickly cater- 
pillars which are common on the stinging-nettle, where they live 
in companies, and suspend themselves by the tail. When the 
time approaches at which the caterpillars of this species ought to 
undergo their transformations, they usually leave the plant which 
had up to that time served them as food. After having wandered 
about a little, they select some convenient spot, where they hang 
themselves up head downwards (Figs. 102, 108). 
In order to hang itself in this way, the caterpillar begins by 
covering, with threads drawn in different directions, a pretty 
large extent of the surface of the body against which it wishes 
