OBJECTIONS ANSWERED. 15 



of considerable utility, even in this view, and may be regarded in some 

 sort as a necessary or at least a very useful concomitant of many arts and 

 sciences. 



The importance of insects to us both as sources of good or evil, I shall 

 endeavour to prove at large hereafter ; but for the present, taking this for 

 granted, it necessarily follows that the study of them must also be im- 

 portant. For when we suffer from them, if we do not know the cause, 

 how are we to apply a remedy that may diminish or prevent their ravages ? 

 Ignorance in this respect often occasions us to mistake our enemies for 

 our friends, and our friends for our enemies ; so that when we think to do 

 good we only do harm, destroying the innocent and letting the guilty 

 escape. Many such instances have occurred. You know the orange- 

 coloured fly of the wheat, and have read the account of the damage done 

 by this little insect to that important grain ; you are aware also that it is 

 given in charge to three little parasites to keep it within due limits; yet at 

 first it was the general opinion of unscientific men, that these destroyers 

 of our enemy were its parents, and the original source of all the mischief. 1 

 Middleton, in his " Agriculture of Middlesex" speaking of the Plant-louse 

 that is so injurious to the bean, tells us that the lady-birds are supposed 

 either to generate or to feed upon them. 2 Had he been an entomologist, 

 he would have been in no doubt whether they were beneficial or injurious; 

 on the contrary, he would have recommended that they should be en- 

 couraged as friends to man, since no insects are greater devourers of the 

 Aphides. The confounding of the apple Aphis, or American blight 

 (J. lanigera 5 ), that has done such extensive injury to our orchards, with 

 others, has led to proceedings still more injurious. This is one of those 

 species from the skin of which transpires a white cottony secretion. 

 Some of the proprietors of orchards about Evesham, observing an insect 

 which secreted a similar substance upon the poplar, imagined that from 

 this tree the creature which they had found so noxious was generated; 

 and in consequence of this mistaken notion cut down all their poplars. 4 

 The same indistinct ideas might have induced them to fell all their larches 

 and beeches, since they also are infested by Aphides which transpire a 

 similar substance. Had these persons possessed any entomological know- 

 ledge, they would have examined and compared the insects before they 

 had formed their opinions, and being convinced that the poplar and apple 

 Aphis are distinct species, would have saved their trees. 



But could an entomological observer even ascertain the species of any 

 noxious insect, still in many cases, without further information, he may fail 

 short of his purpose of prevention. Thus we are told that in Germany 

 the gardeners and country people, with great industry, gather whole 

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

 rassic<z), and then bury them, which, as Roesel well observes 5 , is just as 



1 Kirby, in Linn. Trans, iv. 232. 235. See also a letter signed C. in the 

 Gent. Mug. for August, 1795. This little insect produces no galls like many of 

 the species of the genus (Latr. Gen. Crust, et Ins. iv. 253. Meig. Dipt. i. 94 ), yet 

 it corresponds with the characters of Cecidomyia laid down both by Latreille and 

 Meigen. 



P. 192. 



5 See Latr. Families Natvrelles du Regne Animal, 420. This insect has had 

 four generic names given to it. Lachnus by Illiger, Eriosoma by Leach, Myzoxyle 

 by Blot, and Schizoneura by Hartigin Germar's Zeitschr.f. d. Entomol. 

 r 4 Collett, in Month. Mag. xxxii. 320. 



* Koesel, I. iv. 170. 



