THE PLANT LICE. 



115 



three ocelli, and short legs with the femora thickened, adapting the insects for springing, which they 

 do with as much activity as the Froghoppers. The tarsi are of two joints, and the fore wings are 

 generally somewhat leathery. These are minute insects which live upon various plants and trees, 

 each species, however, usually being restricted to some particular kind of plant. Their bodies, especially 

 those of the larvae, generally show a powdery white coating, analogous to that noticed as occurring in 

 the Fulgoridse. The species rarely exceed an eighth of an inch in length. By attacking the young 

 shoots, and especially the inflorescence of trees, the larvae often give rise to considerable deformation 

 of the parts. Common species occur upon the alder, the ash, the pear-tree, the oak, and the nettle. 



FAMILY XVIIL APHIDIDJE. 



This exceedingly interesting family, which includes the insects commonly known as " Plant Lice," 

 is so abundantly represented everywhere, that some of its forms must be familiar to all our readers. 

 Every one must have noticed the green Aphides which swarm upon roses, and the black ones of the 

 bean, whilst a host of other species, more or less resembling these, are to be found upon almost every 

 plant in the garden or the field. Small and feeble as they are, they often force themselves upon 

 the attention of the farmer and the gardener by the injury they do to cultivated plants. In 

 England the abundance or scarcity of the Hop Fly (Aphis, or Phorodon humuli) is a most important 

 matter to the cultivator of hops, whilst in France and in other wine- ^ 



growing countries the spread of another species (Phylloxera vastatrix) has 

 become a matter of national importance. /' r " 1 



The creatures, which are enabled by their excessive numbers to produce 

 such serious results, are 



individually of the very 

 feeblest. They have a 

 soft, tender body, gene- 

 ally of an ovate shape, 

 and usually long, thin, 

 and feeble legs ; their 

 tarsi are of two joints ; 

 their antennae are more 

 or less elongated, com- 

 posed of from five to 

 seven joints ; the crown 

 of the head has no ocelli; 



and the rostrum is three-jointed, sometimes very long, but sometimes altogether wanting in certain 

 developmental forms. The wings also are frequently deficient, sometimes in all the individuals of a 

 species, sometimes again in particular developmental forms. When present they are membranous, 

 with few veins, generally resting in a roof-like form over the abdomen, and the hind wings are much 

 smaller than the anterior pair. In most of the species the abdomen bears a pair of tubes or perforated 

 tubercles upon the last segment but two. From these, which are known as honey-tubes or corniculi, 

 a sweet fluid is poured forth in small drops, and is a great attraction to Ants and many other 

 Hymenopterous and Dipterous insects. When secreted in great abundance this fluid often drops 

 from the brandies of the trees infested by Aphides, and is then commonly known as "honey-dew." 



These insects generally live on the leaves and tender shoots of trees, shrubs, and herbaceous 

 plants, the tissues of which they pierce in order to suck out the juices. They are sluggish creatures, 

 generally remaining fixed in the same spot, with the rostrum deeply inserted ; but they can shift 

 their position to short distances by slow and feeble walking, and make wider excursions by the aid of 

 the wings with which some forms of each species are generally provided. In many cases the attacks 

 of the Aphides are directed to the roots of plants, and some of these are taken possession of by 

 Ants, who treat them as herds of miniature milch-cows (see Vol. V., p. 381), but it seems doubtful 

 whether these forms, which are always apterous, are more than stages of the development of species, 

 other forms of which live above ground. A few species belonging to the genus Lachnus and its 

 allies, which have the rostrum very long, live in the fissures of the bark of trees. One example, 



ROSE APHIS. 



