( cxix ) 



species not limited to some particular kind of tree, how few 

 are the insects that we can beat out, in comparison with the 

 abundant leaves that fulfil their functions, reach maturity, 

 and then fall off in such numbers as to form a dense carpet in 

 the autumn ! 



Consimiption by particular species. 

 Take a specific case, for example that of the common 

 Gonepteryx rhamni, feeding exclusively in this country on the 

 Rhamnus catharticus, scattered through our upland shaws, or 

 the Rhamnus frangula, frequent in our lowland woods. How 

 slight are its ravages, aided as they are by several other 

 species ! How rarely, indeed, do we find any tree or any 

 hedge or wood so eaten down that either the plant itself has 

 been killed or its summer outburst of leaves so consumed as 

 to cause the starvation of nearly all the larvae, or even of a 

 very large proportion of them ! 



Let me, before passing on, refer to some species famous for 

 their destructive ravages. We have all seen oak trees with 

 their spring crop of leaves cleared off by the larvaj of the 

 little green Tortrix viridana, or a field of cabbages reduced to 

 skeletons by hordes of the gregarious larvje of Pieris brassicse ; 

 but enormous numbers of each species still reach the pupal 

 stage. "We have often seen a hawthorn hedge or several 

 neighbouring hedges nearly cleared of leaves by the gregari- 

 ous web-spinning larvse of Yponomeuta padella, to such an 

 extent that probably many were starved, but a vast number 

 must have eaten their fill. Nor is the productive capacity of 

 the hedge, limited as hedges always are in extent of area, 

 materially affected in the future, for next year the hedge 

 presents an abundant repast. 



There are countries in which doubtless the destruction is 



greater than in our own. We in England have no experience 



of the ravages of Ocneria disjxcr, of Psilura monacha, or of the 



dreaded " army worm," such as they have in Germany or the 



United States, but, however great the destruction may be in 



particular years, the food supply left is so great on the whole 



as to leave enough to perpetuate these as veritable plagues.* 



* Such outbreaks where they occur seem to be sometimes "countered" 

 as regards further destruction in the same area by the habit of emigration, 



