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 manceuvre, 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 — 
ofan 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 larva are polyphagous, or feed upon a 
variety of plants ; amongst others that of the yellow-tail moth (Porthesia 
chrysorrhea) ; 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, ind 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? ; 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 countr 
are not indigenous, but have been imported. It was thus that the mot 
(Galleria Mellonella) so destructive in beehives, and the asparagus beetle 
(Crioceris Asparagi), were made denizens of Sweden.2 The insect that 
has destroyed all 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 
1 Phiylologia, 518, 2 Fn. Succ 667. 1383. 
