•^ Mr, CuRTis's Ohfervathns on Aphides, 



alfo attach, themfelves to the bark of trees, like the Aphh Jal'icis^ 

 which being one of our very largefl fpecies, and hence poflefling 

 fuperior ftrength, is enabled to penetrate a fubdance harder than the 

 leaves themfelves. 



As among caterpillars we find fome that are conftantly and un- 

 alterably attached to one or more particular fpecies of plants^ and 

 others that feed indifcriminately on moft forts of herbage ; fo it is 

 precifely with the Aphides: fome of them are particular, others more 

 general feeders. 



As they refemble other infe6ls in the above refpe6l, fo do they 

 alfo in being infinitely more abundant fome years than others; and 

 though, with regard to certain infers, this variation (fometimes 

 wonderful in the extreme, as in the brown-tail moth which ravaged^ 

 the quickfet hedges in 1782) is not eafily accounted for, it is fohed. 

 without much difficulty as to the Aphis^ as will be fhown in the 

 fequei. In the year 1793 ^^^^Y ^^^^ the chief, and in 1798 the fole,. 

 caufe of the failure of the crop of hops. In 1794, a feafon almoft 

 unparalleled for drought, the hop was perfectly free from them, 

 while peas and beans, efpecially the former, fuffered very much 

 from their depredations. Beans were in 1798 almoft wholly cut 

 off by them; indeed they fuffer more or lefs every year by a black 

 fpecies of Aphis^ particularly the latter crops. To potatoes, and even 

 to corn, we have known them fome years prove highly detri- 

 mental, and no lefs fo to melons. To plants in ftoves, green-- 

 houfes and' frames, where, from the warmth and fhelter afforded ' 

 them, a preternatural multiplication takes place, they prove ex- 

 tremely injurious, and many a rare and valuable plant alfo in 

 the open ground of our botanic gardens falls a vi£tim to thefe 

 general depredators. Seeing, therefore, that our neceffaries as well as 

 luxuries of life are fo materially affecled by the infe6ls of this genus, 

 ail attempt to afcertain fome of the curious and important facls 

 9 relative 



