Practical Lessons on Insect Life. BY THEODORE WOOD, M.E.S., No. XIII. THE HOMOPTERA. AS has already been mentioned in one of the earlier papers of this series, the Homoptera and the Heteroptera are often considered to form sub-orders only, being collectively known as Hemiptera, By those who follow this system they are respectively termed Hemiptera-Homoptera, and Hemiptera-Heteroptera. As, however, the distinguishing features of the two groups are very strongly marked, we will consider them as forming separate orders, to the first of which, the Homoptera, the present paper shall be devoted. The Homoptera include a number of insects many of which appear to be totally dissimilar from one another, and it is not until we carefully examine the structural characteristics that we find them to possess any family resemblance. The distinguishing features of the order may be briefly summed up as follows. In the first place, the structure of both the upper and the lower pairs of wings is of a similar nature, whence is derived the title of Homoptera,' a word signifying 'same-winged,' and therefore very appropriate. These wings are membranous, the upper pair being slightly longer than the lower, which they entirely conceal when the insect is at rest. They do not overlap, however, the sutural margins running parallel with one another, just as is the case with the elytra of the Coleoptera. The body is very convex, causing the wings to assume a rather curious position when not in use. This attitude is not easily described, but may easily be seen by an examination of one of the 'frog-hoppers' which are so plentiful in all parts of the country. The mouth is situated on the lower surface of the head, and is furnished with a beak, or proboscis, by means of which the juices of the plants upon which the insect feeds can be imbibed into the system. This proboscis is merely a modification of the mandibles and the maxillæ, which are considerably elongated, and enclosed in the labrum, which forms a kind of sheath for the whole. In all these insects the pupa is active, and generally bears a considerable resemblance to the perfect insect, the chief distinction, of course, lying in the absence of wings. There is yet another characteristic of the insects of this order, however, and that a very important one, for upon it is based the present arrangement of the group. This is found in the structure of the tarsi, which, in the Homoptera, are never found to consist of more than three joints. They may, however, have less, and Mr. Westwood has divided the insects of the order into three groups, namely, those which possess three joints in the tarsi, those which have two joints, and those in which one joint only is to be found. The first of these groups is scientifically known as the Trimera, and is sub-divided into three families, of two only of which we have representatives in this country. In all the insects of this group the antennæ are very short, and are terminated by a slight bristle. Of the first family, the Cicadida, we have only one British representative, and that solitary exception is so rare that it is very seldom seen, even by working entomologists. This insect, the lower surface of which is represented in the accompanying woodcut, possesses no popular title, probably on account of its rarity, but is scientifically known as Cicada anglica. Cicada anglica. Many of the foreign cicadas, that is, as far as the males are concerned, possess the faculty of uttering a very loud and shrill cry, which is audible at a considerable distance. This sound is produced by a pair of tightly-stretched membranes found beneath the thorax, which are protected by a horny plate easily visible upon examination. It has not as yet been ascertained whether our British cicada is musical or not, although the probabilities are that it is so. It is true that a specimen of the male insect was kept in captivity for a couple of days without being heard to utter a sound, but this period of time cannot be considered sufficiently long to warrant us in coming to any definite conclusion upon the subject. It is much to be hoped that the next person who is fortunate enough to meet with a male cicada will endeavour to set this mooted point at rest. The female cicada is furnished with an ovipositor of rather curious form, resembling a double spear with strongly serrated edges. By means of this instrument the insect is enabled to bore a hole in the substances in which her eggs are to be deposited. The larva dwells in burrows in the earth, which it excavates by means of the very powerful fore-limbs. These tunnels sometimes extend to a considerable depth, some of the foreign cicadas sinking their habitations more than three feet into the ground. The representation of the cicada which accompanies this description shows very clearly the peculiar form of the head, which is common to all the insects of the family to which it belongs, and also illustrates the manner in which the proboscis is packed away beneath the body when not required for use. The form of the body, too, is very well depicted, and, were it not for the size, the woodcut would serve as a very efficient illustration of the lower surface of almost any of our British Trimera. Of the second family of this group, namely, the Fulgorida, or Lantern-flies, we have no British examples, and, as our space will not allow us to describe any of the foreign homoptera, we must pass to the third and last family of the trimera, namely, the Cercopida. These insects are more familiarly known by the title of 'Frog-hoppers,' as they are popularly termed when they have arrived at the perfect stage of their development, and by that of 'Cuckoo-spit,' by which they are generally known while yet in the larval condition. There must be few, indeed, who have ever possessed the use of a garden, or enjoyed a country walk during the summer months, who have not noticed the peculiar masses of frothy substance to be seen upon the stems of many plants, and which are frequently in such abundance as to completely drench the lower garments of the pedestrian. This frothy secretion is popularly considered to be composed either of the saliva of the cuckoo or of that of the frog, to which notion are owing the popular titles both of the larva and the perfect insect. In reality, it is formed in a very singular manner. Driving its beak into the skin of its food-plant, the grub extracts the juices which constitute its nourishment. When they have passed through the system, these juices are exuded in the form of the frothy substance with which we are so familiar, and which covers the entire body of the larva. At occasional intervals the bubbles of which this frothy mass consists resolve themselves again into a liquid form, a drop every now and then falling to the ground, while another slowly takes its place, following the first, after a time, in like manner. In the insects of this group the hinder limbs are formed for leaping, and are endowed with truly wonderful powers. It has been calculated that by their aid one of these Hoppers can leap to a distance equal to seventy times its own length; much the same as if a man were to spring over four hundred feet of ground at a single bound. In order that they may be enabled to obtain a firm purchase upon the ground while preparing for these wonderful leaps, the hinder tibiæ are armed with a number of sharp spines, which afford the requisite foothold. None of the insects of this division possess the curious sound-producing apparatus found in the cicadas. The most striking insect of this group is the Scarlet Hopper (Cercopis sanguinolenta), which may occasion Scarlet Hopper (Cercopis sanguinolenta). ally be seen resting on the leaves of the common bracken upon a sunny morning in the early summer. It is a remarkably handsome creature, which, once seen, can by no possibility be mistaken, the bold scarlet and black markings at once pointing it out from amongst its congeners. This is by no means a rare insect, although it is very local, so much so, indeed, that it is often found to be confined to a few square yards of ground. Easily detected, on account of its brilliant colouring, it is by no means so readily captured, making one of its tremendous bounds at the slightest sign of approaching danger, and being quickly lost to sight among the herbage. Many other frog-hoppers are known to inhabit this country, but they are, as a rule, so plain and insignificant to ordinary examination, and so similar to one another in their habits, that there is no necessity for us to expend space upon their description. We will therefore pass to the next group of the Homoptera, namely, the Dimera, or those in which two joints only are found in the tarsi. This division includes the insects popularly known as Plant-lice, or Green Blight, and scientifically as Aphide, which are such terrible enemies to the horticulturist. Aphis (Winged jorm). These little insects are by no means formidable individually, but become so from the vast numbers in which they are found. They are wonderfully prolific, and that in a manner quite different from that which is customary with insects in general. Aphis (Apterous form). For, in these insects, the peculiar method of reproduction termed Parthenogenesis is strikingly exemplified. A female Aphis, kept entirely isolated from the other sex, will produce female young, and female young only, at the rate of fourteen or fifteen per diem, which, strange to say, pass through no preliminary stages of development, but are brought forth in a perfect condition, differing only in size from their parent. These in their turn give birth to a third generation, and so on. This strange method of reproduction has been known to extend over a space of several years, during the whole of which time no male aphis had been allowed access to the insects. This will account for the wonderfully rapid rate at which the aphides increase, myriads appearing where only a few days previously not an example was to be The birth of prolific females of course increases the reproductive powers to a wonderful extent, and there are few creatures which multiply with the extreme rapidity of the aphis. seen. Now and then the aphis does lay eggs, but this is the exception, and not the rule, the usual method of reproduction in this extraordinary insect being by the parthenogenesis above described. Although individually an aphis can scarcely do any appreciable harm to a plant, the extraordinary numbers of the aphides render them a most terrible pest to agriculturists. There are few plants or trees to which some species of aphis does not attach itself, and which do not suffer very considerably from the ceaseless persecutions of its tiny foes. The hop, especially, is a particular favourite with these little insects, and, were it not for the attacks of the ladybirds, the lacewing-fly, and many other insects which find in them their principal food, the cultivation of this plant would be an absolute impossibility. Gardeners, also, know only too well the ravages caused by the blight' upon many of their favourite flowers, and vainly exhaust their energies in devising means to extirpate their destructive foes. Yet, by a marvellous provision of nature, the enemies of the blight seem always to appear in proportion to the numbers of the pest. If our walls and windows are overrun with ladybirds, we may be sure that the blight has appeared in unusual numbers in the neighbourhood, and that its natural enemies have followed it in order to perform their appointed work of destruction. Sometimes, in the hop-grounds, these creatures may be seen literally in myriads, testifying by their numbers to the service they have rendered the agriculturist in destroying his terrible enemy. The reader will remember that the frog-hoppers, which were described in the earlier portion of this article, exuded the vegetable juices which had passed through the system in the form of a mass of bubbles. The aphis behaves in a somewhat similar manner, ejecting the liquid through two minute tubes which project from the upper surface of the abdomen. The fluid, however, does not appear in the frothy form with which we are familiar in the case of the frog-hoppers, but is merely distilled into limpid drops of liquid, which successively fall upon the leaves on which the insect is resting. This honeydew,' as it is termed from its sweetness, is a favourite beverage with ants, which, strange as it may appear, actually carry the aphides off to their nests, in order to procure an unfailing supply of the coveted dainty. Very often an ant may be seen upon the leaf of some plant or tree tapping an aphis gently with its antennæ, in order to induce the insect to exude a drop of the saccharine fluid, which is eagerly licked up as soon as it makes its appearance at the extremity of the abdominal tubes. It is also said that the ants are in the habit of guarding their herds from the attacks of the hymenopterous parasites which are constantly seeking an opportunity of depositing their eggs in the bodies of their victims, and that they are always on the watch for the appearance of the winged parasite. There are several kinds of aphis to be found in this country, but as all are very similar in habits it is needless to particularize any one species. Closely allied to the preceding insects are those curious aphides which have received the generic title of Eriosoma, i.e., 'wool-bodied,' for the reason that their bodies are covered with a substance resembling fine cotton wool. These creatures are popularly known as American Blight. The woolly substance with which the bodies of these aphides is covered far exceeds in bulk the insects themselves, which it renders so light in proportion to their size that they are blown hither and thither by the least gust of wind. Should they once find their way to the branches of an apple-tree, the fate of that tree is sealed, unless immediate measures are taken for the extermination of the pest. Creeping into the crevices of the bark, the insects form a settlement, and quickly make their way over the entire tree, which speedily becomes overspread with the white cottony substance which covers the bodies of the aphides. Before very long, the tree fades, withers, and finally dies; why, no one can tell. Mr. E. Newman tells us, in his well-known 'Letters of Rusticus,' that the only way of extirpating this destructive pest is by the free application of melted size to the affected trees, not even the smallest patch of the woolly substance being allowed to escape. This, he says, is far superior to the whitewash used in many orchards, which, besides being comparatively ineffectual, completely ruins the appearance of the trees. In the winter-time the aphides retire to the earth at the foot of the tree in order to gain protection from the chilling cold. It is then advisable to turn over an inch or so of the soil upon every frosty day in order that the concealed insects may be killed by the exposure to the cold, These aphides are not furnished with the abdominal tubes through which the honey-dew is distilled, that liquid being produced only by the insects of the preceding group. The last of the three groups of the Homoptera consists of the Monomera, or those in which the tarsus is composed of a single joint only. These creatures, which are popularly known as Scale Insects, or Mealy Bugs, and scientifically as Cocci, are all included in a single genus. These are in many ways most extraordinary insects, the females especially seeming actually to deteriorate as they approach the perfect condition. Indeed, when the final stage of their development is attained, the female cocci become, as Mr. Westward justly remarks, more like galls than living creatures, 'losing all trace of articulation in the body as well as of articulated limbs, and leaving inert and fixed masses of animal matter, motionless, and apparently senseless.' During the earlier stages of their development the sexes are very similar in appearance, both being very active at this period of their existence. After some little time they insert their beaks into the bark of some twig, or the veining of a leaf, and remain motionless, increasing, meanwhile, very rapidly in size. In this position they pass the winter, at the end of which the males take to themselves wings, and fly away in search of their mates, while the females remain fixed as before. The male coccus presents a very different appearance from his obese and unwieldy mate, being really quite a handsome insect. The body is of a deep red colour, while the two wings are of an opaque white, edged with a band of deep crimson. He is very much smaller than the female, and, indeed, presents so totally different an appearance that the two would never be taken for the same species. The eggs deposited by the female are about two thousand in number, and are enveloped in a kind of woolly substance which entirely conceals them from view. As soon as they are laid the parent insect dies, her body flattens and becomes shrivelled and hard, and forms a kind of covering for the eggs, which are situated beneath it. The British cocci are terrible nuisances to the gardener, more especially in hot-houses, where they wreak considerable havoc among the flowers. Some of the foreign species, however, are directly useful to mankind, the well-known Cochineal Insect (Coccus cacti) being one of these. From another species, the Lac Insect (C. lacca) we obtain our sealing-wax, and a peculiar kind of wax from a third, C. ceriferus. The British species, however, have as yet been brought to no practical use. (To be continued.) |