DAMAGE CAUSED BY ANIMALS. 179 



The spanworm is, like the caterpillar of the Pine Beauty, very 

 sensitive to atmospheric influences and changes in temperature, 

 whilst both caterpillars and chrysalides have also numerous 

 enemies that render material assistance in keeping down any 

 tendency towards too prolific increase. But when, despite these 

 checking influences, large swarms actually occur to anything like a 

 calamitous extent, epidemics due to fungoid infection usually soon 

 break out among the caterpillars, and with such virulence as prac- 

 tically to kill them all off very rapidly. 



As a protective or an exterminative measure, swine may be 

 driven into the woods during autumn and winter, to rout out the 

 pupse ; or the shaking and tapping of poles may be resorted to 

 during summer in woods where the presence of the spanworms 

 has been observed. For crops that are badly infested, Altum 

 strongly recommends the raking together of the dead foliage in 

 heaps or lines late in autumn, as the caterpillars and chrysalides 

 thus laid bare on the strips cleared of foliage are more accessible 

 to birds, and perish from the cold during winter, whilst those 

 lying under the heaps of dead needles never attain development 

 during the following spring. But this measure is only applicable 

 when the plague of insects is concentrated within a comparatively 

 small area. On poor soils it is essential, for the maintenance of 

 their productive capacity, that the dead foliage should be replaced 

 in its normal position during the following spring ; and even on 

 the better classes of soil this will also be certainly advisable, 

 though not so absolutely necessary. 



D. LEAF-KOLLERS (TortriMse). 



83. The Pine-slwot Tortrix or Pine Twig -twister, Tortrix 

 (Retinia) buoliana. 



(Vide Plate IV. fig. 23.) 



Though small, this can under certain circumstances become a 

 very dangerous insect in woodlands. This butterfly, or rather 

 moth, has a span of about 0'8 inches. The narrow upper wings 

 and the front part of the body are yellowish-red in colour, with 

 silvery-white, sinuous, transverse bands across them, having a 

 bluish tinge about the middle, and with greyish-white edging; 

 the lower pair of wings are of a glossy, silky grey, also tipped 



