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186

STREPSIPTERA.-HOMOPTERA,

to an extraordinary size in proportion to the rest of the animal. The larvæ appear to feed upon the fatty matter in the bodies of the Bees and Wasps, on which they are found, without injuring their vital parts; and their production does not seem to cause the death of the animals they infest. When full grown, their heads may be seen projecting between the segments of the abdomen of the Bee (Fig. 411, a). Here, too, they undergo their metamorphosis into the pupa state; remaining still inclosed in the larva-skin, and bursting through both the larva and pupa cases, to make their way forth as perfect insects. No distinct mouth has been discovered in the larva, and its mode of obtaining nourishment is unknown. Many points in the economy of these singular insects are still uncertain; especially all that concerns their reproduction. All the specimens yet discovered appear to be males; and it has not been yet ascertained when and how the eggs are laid, or at what stage in the growth of the animals infested by them, the parasites first make their appearance.

ORDER VI.-HOMOPTERA.

715. THE Insects of this Order are distinguished from all others which have, like them, the mouth adapted for suction, by possessing two pairs of wings, usually composed of a firm membrane, and not covered by scales; and by having the anterior pair, whatever may be their consistence, of the same substance throughout, and roof-like when folded. They present many curious anomalies both in structure and habit; so that it is difficult to assign any general character that shall include them all. It is in the structure of the mouth that there is the greatest agreement; this is adapted for suction, the tongue being elongated and channelled like a gutter, and being surrounded by delicate lancet-like organs, with which the tissues of plants are pierced. All the Insects of this group subsist on vegetable juices; and some of them, from the amount of damage they commit, are very injurious to the cultivator. Some of the females are furnished with an ovipositor, provided with several

CICADIDE, OR CICADAS.

187

toothed saws; and with this they make incisions into the leaves and stems of plants. This Order may be divided into sections, like the Coleoptera, according to the number of joints in the tarsi. These sections are only three in number: in the first, TRIMERA, the tarsi are three-jointed; in the second, DIMERA, they are but two-jointed; and in the third, MONOMERA, they have but one joint.

716. Section I. TRIMERA. The three-jointed division of the Homoptera includes three families, the CICADIDE, or Cicadas, the CERCOPIDA, or Froth-hoppers, and the FULGORIDE, or Lantern-flies.-The CICADIDE are the largest of the Order; one

species measuring between six and seven inches in the expanse of its wings. They are nearly all inhabitants of tropical or the warmer temperate regions; only one small species having been found in this country. They have large transparent wings, but are not very active in their habits; being generally found upon trees or shrubs, whose juices they suck. The female makes a succession of slits in the small twigs with her ovipositor, and deposits her eggs in these; the young larvæ soon quit their birth-place, however, and descend to the ground, where they increase in size and become pupæ. It is a species of Cicada inhabiting a kind of Ash, which, by puncturing it, causes it to discharge the sweet, slightly purgative, substance, that is known as Manna. Of the peculiar sound-producing powers of the Cicadidæ, an account has been elsewhere given (ANIM. PHYSIOL. § 679). The ancient Greeks used the Pupa and perfect insects as articles of food.

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FIG. 412.-CICADA.

717. The FULGORIDE bear a general resemblance to the Cicadidæ, but are generally destitute of organs for producing

188

FULGORIDE, OR LANTERN-FLIES.

CERCOPIDE.

sound, and have the legs more adapted for leaping. Many of them are distinguished by a curious prolongation of the forehead, which sometimes equals the rest of the body in size. The shape of this projection varies extremely in the different species, which are numerous in many tropical regions. It is in it, that the

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regard to it not being sufficient. If it really exists, it is only at particular seasons. The Lantern-fly of Guiana seems to be an exception to the general rule, with respect to the absence of sound-producing powers in this Order; for it produces, from sun-set to sun-rise, a loud sound which has been compared with that of a razor-grinder at work.

718. The family CERCOPIDE consists of insects of small size; many of which are remarkable for the grotesqueness of the forms they assume. Several species are inhabitants of this country, and are known under the name of Frog-hoppers, from their leaping powers; or of Froth-hoppers, from their peculiar frothy secretion; or of Cuckoo-spits, from the supposed origin of this fluid.

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an extraordinary development of the first segment of the thorax. The insects of this family are often beautifully varied in their colours; they are constantly found upon plants, upon the juices

FROTH-HOPPERS.-APHIDE, OR PLANT-LICE.

189

of which they subsist in all their stages; and some of them are employed by certain species of Ants, for the same purposes as the Aphides (§§ 694 and 719). The Aphrophora spumaria is one of

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upon willow-trees; and the exudation is sometimes so abundant, from the large number of these animals, that persons walking beneath are wetted by the continual dropping of the fluid. A species nearly allied to this, inhabiting Madagascar, discharges a clear instead of a frothy fluid; and this in such quantities, that it falls to the ground in the middle of the day, when the heat is the greatest, in a continual shower.

719. Section II. DIMERA. This section entirely consists of minute insects; of which the most remarkable family is that of APHIDE, or Plant- Lice. These live in great numbers upon the surface of plants of almost every description, and suck the juices, by means of their proboscis, from the young shoots, leaves, stems, and even roots. They greatly weaken its vigour, and often distort young shoots and leaves; some species cause little gall-like excrescences by the irritation they produce. From two horn-like processes at the posterior part of their bodies, a saccharine secretion exudes, of which Ants are very fond (§ 694); and it is either this fluid dropped on the adjacent leaves, or the extravasated sap flowing from the wounds made by the insects, which is known under the name of honey-dew. In many of the species of this family, a large proportion of the individuals never acquire wings; in which case the Pupa is not to be distinguished from the Larva or Imago; whilst at certain parts of the year, other individuals of the same species, and of both sexes, acquire wings. The wingless Aphides, which may be seen in the spring and early summer, are all females capable of producing

190

APHIDES, OR PLANT-LICE.-COCCIDÆ.

fertile eggs; and from these are reared the winged males and females, which are seen later in the season. Their rapidity of production is enormous; nine generations having been produced within three months, and each generation averaging 100 individuals. Hence it may be calculated that, from a single Aphis, 10,000 million millions may be generated in that short period. It is not surprising, then, that an immense amount of damage should be done by them, notwithstanding their very small size. Many of the blights so injurious to the gardener and the agriculturist, consist really of Aphides; although from the minuteness of the insects themselves, they frequently escape observation. The Aphis Rosa, or Rose Louse, is one of those best known to the gardener; whilst the one most destructive to the property of the cultivator on a larger scale is the Aphis Humuli, or Hop Fly. Of the extent of its influence on the production of that vegetable, some idea may be formed from the fact, that the duty paid to the English government on its growth, has varied from 468,000, to 15,400. in different years, almost entirely from the absence of this insect in the former case, and its presence in the latter; and the difference in the actual value of the crop is, of course, far greater.

FIG. 416.-APHIS ROSE.

720. Section III. MONOMERA. The third section contains but one family, that of COCCIDE, sometimes called Scale Insects. These, although ordinarily of very small size, are amongst the most injurious to vegetation of the whole tribe. Like the last, they are remarkable for their powers of propagation; and when they once gain possession of a plant or young tree, its death is almost certain, the minute size of the larvæ rendering it almost impossible to exterminate them. They furnish, however, some very important products. The bodies of many species are deeply coloured through their whole substance, and yield dyes of great value; the richness of which seems to depend upon the nature of the plant on which they feed. The Coccus of the ancients was a native of the Levant; but that which furnishes the Cochineal so highly valued at the present time, was originally confined to Mexico, where it feeds on the plants of the Cactus

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