50 RELATIONS OF WOODLANDS TO ANIMAL LIFE. [Xov. 



many of the deciduous species, a new growth of leaves will some- 

 times appear the same season, and the injury will have left its 

 permanent record, in the thin growth of that year. We have seen 

 in the Museums of Forest Academies a cross section of a large tree, 

 several centuries old, in which every third ring of growth for a long 

 period was very narrow, showing the periodical return of an insect 

 that stripped oif tlie leaves, — to lie read tlu'ough a century or more, 

 and in which the exact j'ears could be fixed. 



But where an evergreen loses its leaves, it has no power to 

 recover, and the tree must perish. Althougli in most of these 

 insect invasions our enemies appear by millions, and their destruc- 

 tion while at work is wholly beyond human power; yet human 

 ingenuity has devised various ways for relieving and sometimes of 

 wholly preventing the harm that might have otherwise ensued. 

 This consists largelv in destroving their egcfs, — by inducing the 

 parent insect to deposit them where they may be burned, — to 

 some extent by .spraying the trees with some poisonous substance, 

 by opposing barriers to their progress, and in some cases, as in fruit- 

 trees, by jarring off the insects themselves, and burning them with 

 fire. It must, however, be admitted that nature has provided means 

 for maintaining the halance of life that are infinitel}' more effectual 

 than any device of man. A sudden change of temperature from 

 heat to cold Avill sometimes destroy a wdrole generation. Multi- 

 tudes of minor and microscopic insects prey upon the larger 

 ones, perhaps not killing them at once, but weakening them and 

 destroying their breeding power. Ichneumon flies wiU. lay their 

 eggs in the bodies of larvffi which will live perhaps their full 

 term ; but when the change conies, instead of the perfect insect 

 appearing, it will be the parasite that has grown at its expense. 

 Many of the beetles are carnivorous and live wholly upon other 

 insects or their eggs. They are distinguished from the wood- 

 boring beetles by their quick movements, and the long and sharp 

 points in their jaws. A cold and wet summer may destroy 

 mj'riads of insects, while a hot and dry season is generally favour- 

 able to their increase. 



Among the useful allies of man, in this war with insect life, tlie 

 birds deserve an honourable rank : some of them, like the swallows, 

 feed upon nothing else. The woodpeckers have a way of following 

 the grubs of wood-beetles into the bark and wood, and wherever 

 we see them at work, we may depend upon it, they are after some- 

 thing to eat. 



A lumberman in Maine has informed us, that after great quan- 

 tities of spruce timber in that State had been killed by bark-boring 

 beetles, the woods became filled with the noise that these birds 



