52 OBJECTIONS ANSWERED. 



the gardeners and country people,^ with great industry, gather whole bas- 

 kets full of the caterpillar of the destructive cabbage moth (Mamestra 

 Brassica), and then bury them, which, as Roesel well observes^ is just as 

 if we should endeavor to kill a crab by covering it with water ; for, many , 

 of them being full grown and ready to pass into their next state, which 

 ihey do underground, instead of destroying them by this manoeuvre, their 

 appearing again the following year in greater numbers is actually facilitat- 

 ed. Yet this plan applied to our common cabbage caterpillar, which 

 does not go underground, would succeed. So that some knowledge of the 

 manners of an insect is often requisite to enable us to check its ravages 

 effectually. With respect to noxious caterpillars in general, agriculturists 

 and gardeners are not usually aware that the best mode of preventing 

 their attacks is to destroy the female fly before she has laid her eggs, to do 

 which the moth proceeding from eacli must be first ascertained. But if 

 their research were carried still further, so as to enable them to distinguish 

 the pupa and discover its haunts, and it would not be at all difficult to 

 detect that of the greatest pest of our gardens, the cabbage butterfly, the 

 work might be still more effectually accomplished. Some larvae are 

 polyphagous, or feed upon a variety of plants ; amongst others that of the 

 yellow-tail moth {Porthesia chrysorhoed) ; yet gardeners think they have 

 done enough if they destroy the web-like nests which so often deform 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 distinguish 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 alFd 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 sean hev reated up all'd close." Nor could I con- 

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

 the evil. Even philosophers sometimes fall into gross mistakes from this 

 species of ignorance. Dr. Darwin has observed, 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 attack- 

 ed, and that they diminish very considerably the number 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 

 effect 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 large proportion of the most noxious insects in every country 

 ' » Roesel, I. iv. 17U * Fhytologia, 518. ' 



