INSECTS. 185 



Ash, Elm, Maple, Sycamore, Birch, or Alder. When Oaks have been 

 defoliated in spring by leaf-roller caterpillars, they can utilise their 

 nutrient reserves and flush into leaf again in July ; but when caterpillars 

 have devoured most of the foliage of Scots Pine and Spruce, the recovery 

 of the Pine is doubtful, and the Spruce dies. In Britain, the Larch often 

 suffers severely from mining-moths and leaf-lice. Damage to young crops 

 is more serious than to older poles and trees ; and attacks in spring are 

 worse than those in summer or autumn, after buds are formed for next 

 year's growth. And if foliage alone be attacked, the damage may only 

 be temporary; but when roots and cambium are badly injured, the 

 sapling, pole, or tree usually dies. Injurious insects are, fortunately, not 

 the most prolific kinds. Hard winters are not fatal to most insects, and 

 may favour the increase of beetles (protected by their horny casing) by 

 causing the death of many insectivorous birds. Naked larvse without any 

 protective covering are sensitive to damp cold weather, and are killed in 

 large numbers when moulting their skins. Warm and dry weather, 

 stumps remaining after heavy timber falls, sickly crops of all ages, and 

 dominated or unhealthy trees, all form breeding -places for injurious 

 insects, which then increase with rapidity. Bark- and cambial-beetles 

 lay eggs in stems thrown or broken by wind, or in winter-felled trees left 

 till late spring or summer, or in those already sickly from attacks of other 

 insects on the foliage. Pine-weevils breed in the stumps of recently 

 felled trees, and feed on neighbouring young plantations. Moths usually 

 lay their eggs on backward crops growing on inferior soil, and unable to 

 recover from the injuries of the caterpillars ; and such favourable 

 breeding- and feeding-places form centres from which noxious insects 

 spread to other woodlands. Hence the need for careful tending ; neglect 

 of any one part of a wood is a danger to all of the timber-crops. 



Natural Checks upon Injurious Insects. Wet, cold weather while 

 caterpillars are moulting their skins, and when beetles and moths are 

 pairing, keeps down injurious injects. Before any appear in unusual 

 numbers, the balance of nature must somehow have been disturbed ; 

 and when left to nature the balance is usually restored in 3 to 4 years, by 

 predatory and parasitic insects increasing greatly, and bacterial and 

 fungous diseases breaking out epidemically and almost exterminating the 

 insect. But to await this natural readjustment may mean entire loss of 

 the timber-crops. In mixed woods there are more insectivorous birds 

 than in pure woods (of Conifers especially), and this tends to check 

 excessive increase of noxious insects. So far as considerations of sport 

 permit, all natural enemies of injurious insects should be preserved, the 

 chief among which are the following : 



1. Mammals. Bats devour cockchafers and moths ; moles destroy 



