HOMOPTERA. 303 



appendages which garnish the upper side of the abdomen; 

 while the Aphides are furnished in both sexes with two 

 lateral tubercles. 



The habits of the two families seem to be very similar, 

 and indeed many of the insects commonly called Aphis 

 are really species of Psylla. They are common on apple, 

 pear sometimes, and birch-trees, and Psylla Buxi sets ifs 

 mark on nearly every box-tree we examine, by shrink- 

 ing the terminal leaves into a concave form, so giving a 

 budlike appearance to their clusters. 



Of all English Homoptera, the Aphides, or Plant-lice, 

 are the most destructive and the most universally preva- 

 lent. Their attacks sometimes convert a turnip field 

 into an offensive mass of decay, injuring, and at 

 times destroying, whole crops of all kinds, whilst not 

 sparing even the single little potted geranium in a 

 garret-window. In the hop countries they form a con- 

 siderable feature in the statistics of produce, and the 

 hops would be fairly exterminated by the Aphides if it 

 were not for several enemies already spoken of elsewhere. 

 The Hymenopterous Ichneumons, tiny enough to be 

 hatched, reared, and brought to perfection within the 

 small body of an Aphis, leave the proof of their numbers 

 in the brown swollen Aphis- skins which we may find 

 abounding in any plant frequented by the Aphides. 

 These displaying one small circular hole in the abdomen, 

 tell us of the exit of the little creature which was reared 

 and fattened in the wonderful laboratory in which vege- 

 table juices were transformed into animal food for his 

 sole use and benefit. 



The larva of the Lacefly is another enemy, not however 

 plentiful enough to make much havoc among the legions 

 of the Aphis. The Syrphus larva does the gardener 



