176 NATURAL HISTORY. [CH. X. 



CHAPTER X. 



APHIS, OR PLANT-LOUSE. 



Every Tree, every part of a Tree has its peculiar Species SucJc Vege- 

 table Juices Shelter themselves from bad Weather in the concave 

 parts of Leaves. 



AMONG the most curious of those animals which 

 are parasitical on plants, is the aphis, or plant-louse. 

 It is an insect common enough in our fields and 

 gardens, and there is scarcely a tree or shrub which 

 is not attacked by one or more species peculiar to 

 itself. Some are winged, and others have no wings ; 

 and some are black, green, brown, in short, all co- 

 lours : but however they may vary in these non-es- 

 sentials, their habits and instincts are similar. They 

 live in society, and attach themselves to the stems, 

 the leaves, and roots of shrubs and vegetables, the 

 juices of which they suck by means of a tube, with 

 which they are furnished for the purpose ; and they 

 frequently cling in such numbers to the sustaining 

 plant, as to give it a most unsightly appearance. 



If the rose-tree, or any other plant, be carefully ex- 

 amined, some portion of it will be found covered with 

 little transparent insects of a green colour. They 

 appear to be in a state of perfect repose : they are., 

 however, in reality, diligently occupied in pumping 

 out the juices of the plant. The following is a 

 magnified figure of the insect. The length of the 

 sucking pump or trunk, in some species, extends 

 beyond the body ; when they walk, it is folded under 

 the belly : in the generality, however, the ordinary 

 length of this member is about one-third that of the 

 insect. While employed in using this instrument, 

 they form at times two layers, one over the other ; 



