30 OBJECTIONS ANSWERED. 



pearing again the following year in greater numbers is 

 actually facilitated. Yet this plan applied to our com- 

 mon 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 ra- 

 vages 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 as- 

 certained. 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 but- 

 terfly, the work might be still more effectually accom- 

 plished. Some larvae are polyphagous, or feed upon a 

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

 moth (Bombyx chrysorh&a, F.); 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 last 

 year, when walking with a gentleman in his estate at a 

 village in Yorkshire. Our attention was attracted by se- 

 veral 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 



