THE BBOWN-TAILED MOTH. 445 



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

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

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

 the thickness of the three walls, together with their intervening 

 spaces. 



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

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

 many respects resembles that of the Gold-tailed MotL The 

 nest, however, 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 

 solid, 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 conse- 

 quence, do not need such thick walls. Any hedgerows where 

 nettles are found will supply numerous examples of such nests, 

 made by the curious caterpillars which afterwards assume the 

 lovely and familiar forms of the Peacock and Smat.Ti Tortoise- 

 shell Butterflies {yanessa lo and Vanessa urticce). Great black 

 masses of these caterpillars 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 loosely spun, 

 and forming a kind of net, with long and irregular meshes. 



