OBJECTIONS ANSWERED. 



25 



cabbage butterfly, the work migbt be still more efFectually 

 accomplished. Some larvee are polyphagous, or feed upon a 

 variety of plants ; amongst others that of the yellow-tail moth 

 {Porihesia chrysorhoed) ; yet gardeners think they have done 

 enough if they destroy the web-like nests which so often de- 

 form our fruit-trees, without suspecting that new armies of 

 assailants will wander from those on other plants which they 

 have suffered to remain. Thus will thousands be produced 

 in the following season, which, had they known how to dis- 

 tinguish them, might have been extirpated. Another instance 

 occurred to me, when walking with a gentleman in his estate 

 at a village in Yorkshire. Our attention was attracted by 

 several circular patches of dead grass, each having a stick 

 with rags suspended to it, placed in the centre. I at once 

 discerned that the larva of the cock-chafer had eaten the roots 

 of the grass, which being pulled up by the rooks that devour 

 this mischievous grub, these birds had been mistaken by the 

 tenant for the cause of the evil, and the rags were placed to 

 frighten away his best friends. On inquiry why he had set 

 up these sticks, he replied, " He couldn't beer to see'd nasty 

 craws pull up all'd gess, and sae he'd set'd bairns to hing up 

 some aud clouts to flay 'em away. Gin he'd letten 'em alean 

 they'd scan hev reated up all'd close." Nor could I convince 

 him by all that I could say, that the rooks were not the cause 

 of the evil. Even philosophers sometimes fall into gross mis- 

 takes from this species of ignorance. Dr. Darwin has ob- 

 served, that destroying the beautiful but injurious wood- 

 peckers is the only alternative for preventing the injury they 

 do to our forest trees by boring into them ^ ; not being aware 

 that they bore only those trees which insects have previously 

 attacked, and that they diminish very considerably the num- 

 ber of such as are prejudicial to our forests. 



From these facts it is sufficiently evident that entomological 

 knowledge is necessary both to prevent fatal mistakes, and to 

 enable us to check with eflect the ravages of insects. But 

 ignorance in this respect is not only unfit to remedy the evil ; 

 on the contrary, it may often be regarded as its cause. A 



1 Phytologia, 518. 



