16 OBJECTIONS ANSWERED 



if we should endeavour 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 

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

 appearing again the following years in greater numbers is actually facilitated. 

 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 each must be first ascertained. But if their research were 

 carried still further, so as to enable them to distinguish the pupa and dis- 

 cover 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 

 chrysorrhcea) ; yet gardeners think they have done enough if they destroy 

 the web-like nests which so often deform our fruit-trees, without suspect- 

 ing 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 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 sean 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 mistakes from this species of ignorance. Dr. Darwin has observed, 

 that destroying the beautiful but injurious wood-peckers is the only alter- 

 native for preventing the injury they do to our forest trees by boring into 

 them 1 ; not being aware that they bore only those trees which insects have 

 previously attacked, 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 

 are not indigenous, but have been imported. It was thus that the moth 

 (Galleria MclloneUa) so destructive in beehives, and the asparagus beetle 

 (Crioceris Asparagi\ were made denizens of Sweden. 2 The insect that 

 has destroyed ail the peach trees in St. Helena was imported from the Cape; 

 and at home (not to mention bugs and cock-roaches) the great pest of our 



l Phytologia, 518. 2 Fn.Suec. 567. 1383. 



