INSECTS 



401 



Fig. 920. Silver-Y Moth (Plusia gamma] 

 i, Eggs; 2, caterpillar; 3, chrysalis in cocoon; 4, adult female. 



of the Silver-Y Moth (Plusia gamma, fig. 920), for instance, 

 are to be found on the under sides of leaves, enclosed in a 

 loose web of silk. The much denser cocoons of the Silkworm 

 Moth (Bombyx mori) and other species are familiar as the source 

 of commercial silk. Many caterpillars descend to the ground 

 before they become chrysa- 

 lides, an obviously protective 

 habit. We may take as an 

 example of this the Heart- 

 and-Dart Moth (A gratis ex- 

 clamationis, fig. 921), a com- 

 mon agricultural pest in this 

 country, in which the protec- 

 tive investment is supple- 

 mented by an earthen case. 

 The caterpillar of another 



British species (Brephos notha] belonging to the same family of 

 Owlet- Moths (NoctuicUe) adopts quite a different method. During 

 its larval life it lives upon the aspen, the leaves of which it sticks 

 together to form a shelter. When fully grown it bites out a 

 snug receptacle in bark or wood wherein to become a chrysalis, 

 previously spinning one or more partitions of silk across the 

 entrance to its hiding-place. 

 In this way prying enemies 

 are to some extent kept off, 

 while ventilation is at the 

 same time not interfered 

 with unduly. 



The caterpillars of cer- 

 tain South American Moths 

 (species of Palustra] inhabit 



fresh Water, Swimming" about 

 



by alternately coiling and 

 straightening their bodies. In most, but not all, species they 

 construct their cocoons under water, and a number of these are 

 found associated together. The larva of the Puss- Moth (Ceritra 

 vinuld] makes a particularly firm cocoon, leaving, however, a thin 

 place in front of its head, through which the imago later on 

 forces its way. The exit is assisted by the ejection of a fluid 

 containing caustic potash, which softens the barrier between the 



Fig. 921. Heart-and-Dart Moth (Agrotis exclamationis). 

 i, Adult female; 2, caterpillar; 3, earthen case (cut open) en- 

 closing chrysalis in cocoon (4). 



