986 Distribution of the Large Larch Saw-fly. [march, 



insect has shown unexpected powers of spreading, and the 

 difficulty of fixing an outer boundary for the area attacked 

 is considerable. In general, it has been found that when one 

 wood in a neighbourhood is infested, all the others are so to a 

 greater or less degree, and that even when the attack becomes 

 very attenuated, it is at the same time general. 



Lake District. — The presence of the saw-fly was first noted 

 in 1906. It is probable that the attack had already been in 

 progress two to three years before it was noticed, since 

 experience shows that it is only at the end of two to three 

 years that the insect increases in numbers sufficiently to 

 attract attention. 



The Dodd Wood, from which the pest was first reported, 

 has suffered most, and some 16,000 trees have died as the 

 result of repeated defoliations. From this as a centre the 

 saw-fly has apparently spread over the whole of the Lake 

 District. 



The attack appears to be worst in the neighbourhood of 

 Keswick' and on the Manchester Corporation's Plantations 

 round Thirlmere, where the larch were practically stripped 

 bare by the autumn of 1909. Southwards from Keswick the 

 virulence of the attack becomes less. This is shown on the 

 map drawn by Mr. Hewitt in 1908, 1 and observations made 

 in the vicinity of Windermere, Ambleside, and Hawkeshead 

 during the summer of 1909 confirm this opinion. 



To the east and north the saw-fly has been noted as far as 

 the Eden Valley and Carlisle. It was thought at the time 

 the inspection was made that the absence of large masses of 

 larch north of the Lake District, and the bare Fells to the East 

 of the Eden Valley would stop the spread of the saw-fly north 

 and east, but, as pointed out, the saw-fly has shown unex- 

 pected powers of distribution, and it has been found by inde- 

 pendent investigators further to the east. 



Welsh Area. — There is no evidence to account for the 

 appearance of the saw-fly in Wales. It was reported in 1907 

 as having done considerable damage to a plantation in the 

 vicinity of Dinas Mawddwy, but the probability is that it 

 had already been three or four years in the district. The 



1 Journal, December, 1908, p. 655. 



