MAY 109 



In 1908 only 5"8 per cent, of the cocoons produced 

 ichneumons ; this was nearly doubled in 1909 by a rise 

 to 10-9 per cent., while in 1910 it turned out that no 

 less than 62 per cent, of the cocoons had been visited 

 by ichneumons, whereof the grubs had devoured the 

 larvae of the sawfly. It became apparent in this interest- 

 ing experiment that the sawfly, on arriving in Great 

 Britain, had secured a long start over its natural 

 parasite; but the ichneumon, having overtaken the 

 fly, made up so quickly for lost time that the balance 

 of nature was restored in the course of three or four 

 seasons. 



Now as to the other auxiliary force, the birds. 

 Soft-billed birds — those that are purely or chiefly 

 insectivorous — are seldom permanently numerous in 

 coniferous woods. It occurred to Dr. Hickson that 

 this might be owing to the scarcity of secure nesting 

 places among trees of that class, so he persuaded the 

 Manchester Corporation to provide a number of nesting 

 boxes and have them set up among the larches. How 

 readily the birds availed themselves of this facility may 

 be judged from the following table taken from Dr. 

 Hickson's report for 1912 : 



' And what,' asks Dr. Hickson, ' has been the result ? The 

 result has been that in the summer of 1911, and again in 



