106 MARVELS OF THE ANIMAL WORLD 



that the undue persecution of a given species may 

 upset the balance of Nature, with results that are 

 likely to prove very serious to us. 



Few living creatures are more valuable to man 

 than the insectivorous birds, for they feed upon 

 such destructive pests as bark-beetles, wood- 

 boring beetles, grasshoppers, wire-worms, plant- 

 lice or aphides, weevils, caterpillars, slugs, etc., 

 which, if left to multiply unchecked, would soon 

 cause such injury to trees, foliage, roots and fruits 

 as to obliterate all traces of vegetation from the 

 face of the earth and convert it into a barren 

 waste ; for even in their present numbers their 

 ravages are very pronounced, and a well-known 

 naturalist writes : ' I believe it is no exaggeration 

 to estimate that more trees are annually destroyed 

 in the United States by insects than are destroyed 

 by fire ; and yet more is said about the protection 

 of forests from fire than from insects.' Although 

 the indiscriminate killing of wild creatures may 

 prove very detrimental to man, yet, on the other 

 hand, we have ample evidence that it is not always 

 advisable to introduce them artificially into regions 

 where they have previously been unknown. The 

 havoc wrought in Australia and New Zealand by 

 imported live rabbits has proved a serious nuisance 

 to the agriculturist owing to the astonishing 

 fecundity of the species, and in spite of the fact 

 that many millions are killed every year for the 

 purpose of obtaining their skins, there appears to 

 be little likelihood of their numbers being kept 

 within bounds. Some idea of the difficulties 



