PEACOCK AND SMALL TORTOISE-SHELL BUTTERFLIES. 467 



ing to the scissors so that a straight cut is almost impossible. 

 Delicate walls divide the interior into several compartments, in 

 all of which are evidences that the caterpillars must have resided 

 for some time. The reason why the creatures make this nest is 

 that they are hatched toward the end of summer, and, in conse- 

 quence, are forced to pass the winter in the larval condition, so 

 that some warm residence is needful for them. It is well-known 

 that air is a very bad conductor of heat, and, in consequence, the 

 successive sheets of silk which cover the nest, and which inclose 

 layers of air between them, form a protection which is far warm- 

 er than would be obtained by a solid mass of silk measuring 

 twice the thickness of the three walls, together with their inter- 

 vening spaces. 



There is an allied insect, popularly called the Brown-tailed 

 Moth (Porthesia auriflua), which spins a social nest that in many 

 respects resembles that of the Gold-tailed Moth. The nest, how- 

 ever, is scarcely so elegant, nor is the silken web so beautifully 

 delicate. Much, however, depends upon surrounding conditions, 

 such as the disposition of the twig on which the nest is placed, 

 and the presence or absence of leaves, whether those of the tree 

 or of other plants that happen to grow in close proximity. 



These nests are very firmly constructed, and the walls are sol- 

 id, as is needful for insects which are obliged to pass the winter 

 within them. There are, however, many caterpillars which live 

 socially, and which spin a common habitation, but which leave it 

 before the cold weather comes on, and, in consequence, do not 

 need such thick walls. Any hedgerows where nettles are found 

 will supply numerous examples of such nests, made b}^ the curi- 

 ous caterpillars which afterward assume the lovely and familiar 

 forms of the Peacock and Small Tortoise-shell Butterflies 

 (Vanessa To and Vanessa urticce). Great black masses of these cat- 

 erpillars may be seen upon the nettles, and, on examining them 

 closely, they will be seen to reside within a common home, made 

 of tough silken threads, very loosefy spun, and forming a kind of 

 net, with Ions; and irregular meshes. 



