DAMAGE CAUSED BY ANIMALS. 109 



and difficult ; for under favourable circumstances, their rate of 

 numerical increase is quite extraordinary, and when once they 

 have gained the upper hand, their annihilation is, in the 

 majority of cases, almost hopeless without the -assistance of 

 nature. 



In view of the great danger to which forests, and in particular 

 coniferous forests, are exposed, it is the duty of every Sylviculturist 

 to make himself acquainted with the appearance and life-history 

 of the more important forest insects, and to acquire a knowledge 

 of the best means of obviating and combating their attacks : 

 Forest Entomology, indeed, forms one of the most important 

 branches of the Protection of Woodlands. 



As a basis for the study of Forest Entomology in particular, 

 some general acquaintance with the outlines of Zoology is 

 requisite, so that at all Forest Academies, and all Universities 

 : where Forestry is taught in Germany, a course of lectures on 

 Zoology precedes the special lectures on Entomology. But in order 

 to make the following details intelligible to those who have not 

 I had the opportunity of benefiting by such a course of study, a 

 | few brief remarks may be permitted concerning the character- 

 istics and life-history of insects in general, before proceeding to 

 consider the more important species individually in greater detail. 

 In order to avoid repetitions, mention may, by way of preface, be 

 briefly made of the circumstances favouring, and also those 

 militating against, the numerical increase of forest insects, and of 

 their enemies, likewise of the methods of prevention and 

 annihilation generally employed, together with the measures to 

 be adopted after any unusually large swarms have finished 

 feeding. The general classification of insects will also be referred 

 to in a few words, previous to considering them individually. 



58. On the Life-history of Forest Insects in general. 



Most insects pass through four metamorphoses or different stages 

 of development, each of which distinctly varies from that preceding 

 it. These four different stages of the complete metamorphosis are : 

 1, Ovum, or egg; 2, Larva, the grub or caterpillar; 3, Pupa, 

 or chrysalis ; and 4, Imago, or perfect insect. But in the com- 

 paratively infrequent cases of imperfect metamorphosis, a distinct 

 pupal stage is wanting, the transformation from larva to imago 



