314 



PROTECTION AGAINST INSECTS. 



extensive, and towards its end, the caterpillars return in swarms 

 to the summit of the trees and eat off all the younger shoots. 

 Repeated observation has proved that these caterpillars are all 

 sickly and eventually, die, and inside them a great variety of 

 parasites is found. 



The attack lasts from May till July, and is repeated for about 

 3 years. In the 2nd or 3rd year it culminates, and complete 

 defoliation may kill the whole wood. The spruce is more sensi- 

 tive to the attack than the 

 Scots pine. The latter 

 may recover the loss of half 

 its foliage. 



The process of recovery 

 in the spruce is shown in 

 Figs. 158, 159, which 

 represent portions of trees 

 attacked in Silesia during 

 1855 and 1856. The length 

 of the internodes was least 

 in 1858, the normal growth 

 not being resumed till 

 1861, and a characteristic 

 growth of stunted " bristle- 

 needles" appeared, a fea- 

 ture which not unf requently 



Fig. 160.-Beech leaf" eaten by a caterpillar ? CU1<S in the Case f Scots 

 of Z. monacha, L. pine. 



The insect is found both 



in the plains and in hilly country. The most severe attack 

 by the " Nun " during the present century was during 

 1853-1858 in East Prussia, Lithuania, and Poland ; in 

 1858 a bark-beetle attack followed, and the calamity only 

 stopped in 1860. From the 29th July, 1853, to the 

 27th June, 1855, in the Rothebude Forest, where the 

 attack commenced, 6,375 acres of forest were completely 

 stripped of needles, and about half as much more nearly 

 stripped. The larval droppings covered the ground to a depth 

 of 5 to 8 cm., in many places to 15 cm., and kept falling to 

 the ground with a sound like heavy rain. Up to the 1st 



