INSECTS

From Agepedia

Jump to: navigation , search

INSECTS, in natural history. Under the head Entomology, an account is given of Latreilie's system of this department of natural history. The following description of the characteristics of INSECTs applies to the Crustacea and arachnides, as well as to INSECTs, strictly so called. Insects are not furnished with red blood, but their vessels contain a transparent lymph. This may serve to distinguish them from the superior animals, but it is common to them with many of the inferior; though Cuvier has demonstrated the existence of a kind of red blood in some of the vermes. They are destitute of internal bones, but, in place of them, are furnished with a hard external covering, to which the muscles are attached, which serves them both for skin and bones; they are likewise without a spine formed of vertebra?, which is found in all the superior classes of animals. They are furnished with articulated legs, six or more; this circumstance distinguishes them from all other animals destitute of a spine formed of vertebra?. A very great number of insects undergo a metamorphosis: this takes place in all the winged insects. They frequently change their skin in the progress of their growth. A very great number of insects are furnished with jaws placed transversely. The wings with which a very great number of insects are furnished, distinguish them from all other animals, which are not furnished with a spine composed of vertebra?. Insects are generally oviparous; scorpions and aphides, during the summer months, are viviparous. Insects have no nostrils; are destitute of voice; they are not furnished with a distinct heart, composed of veutri cle and auricle. Incubation is not necessary for hatching their eggs. Insects, like all other organized bodies, which form the animal and vegetable kingdoms, are composed of fluids and solids. In the four superior classes of animals, viz., mammalia, birds, reptiles and fishes, the bones form the most solid part, and occupy the interior part both of the trunk and limbs; they are surrounded with muscles, ligaments, cellular membrane, and skin. The matter is reversed in the class of insects ; the exterior part is most solid, serving at the same time both for skin and bones; it encloses the muscles and internal organs, gives firmness to the whole body, and, by means of its articulations, the limbs, and different parts of the body, perform their various motions. In many insects, such as the crab, lobster, &c, the external covering is very hard, and destitute of organization; it is composed of a calcareous earth, mixed with a small quantity of gelatine, formed by an exudation from the surface of the body. As its great hardness would check the growth of the animal, nature has provided a remedy; all of these crustaceous insects cast their shell annually. The skin of most of the other insects is softer, and organized, being formed of a number of thinĀ¦" membranes, adhering closely to one another, and putting on the appearance of horn. It owes its greater softness to a larger proportion of gelatine. The muscles of insects consist of fibres formed of fasciculi; there are commonly but two muscles to produce motion in any of their limbs, the one an extensor, the other a flexor. These muscles are commonly attached to a tendon, composed of a horny substance, connected to the part which they are destined to put in motion. In most insects, the brain is situated a little above the oesophagus; it divides into two large branches, which surround the oesophagus^and unite again under it, from which junction a whitish nervous cord proceeds, corresponding to the spinal marrow of the superior animals, which extends the ; whole length of the body, forming in its course 12 or 13 knots or ganglions, from each of which small nerves proceed to different parts of the body. Whether insects be endowed with any senses different from those of the superior animals, cannot easily be ascertained. It appears pretty evident, that they possess vision, hearing, smell and touch; as to the" sense of taste, ,we are left to conjecture ; *for we are acquainted With no facts by which we can prove that insects do or do not enjoy the sense of taste. The eyes of insects are of two kinds; the one compound, composed of lenses, large, and only two in number; the other are small, smooth, and vary in number from two to eight. The small lenses, which form the compound eyes, are very numerous; 8000 have been counted in a common house fry, and 1700 in a butterfly. The far greater number of insects have only two eyes; but some have three, as the scolopendra ; some four, as the gyrinus; some six, as scorpions; some eight, as spiders. The eyes of insects are commonly immovable; crabs, however, have the power of moving their eyes. That insects are endowed with the sense of hearing, can no longer be disputed, since froghoppers, crickets, &c, furnish us with undeniable proofs of the fact. Nature has provided the males of these insects with the means of calling their females, by an instrument fitted to produce a sound which is heard by the latter. The male and female deathwatch give notice of each other's presence, by repeatedly striking with their mandibles against old wood, &c, their favorite haunts. Their ears have been discovered to be placed at the root of their antenna?, and can be distinctly seen in some of the larger kinds, as the lobster. The antennas or feelers seem to be merely instruments of feeling, though some naturalists have thought them to be organs of tasting and smelling; and others, of a sense unknown to us. The amazing variety in the mouths of insects, is evident from the fact, that their whole classification, in the Fabrician system, is founded on it. That insects enjoy the faculty of smelling is very evident; it is the most perfect of all their senses. Beetles^ of various sorts, the different species of dermestes, flies, &c, perceive at a considerable distance the smell of ordure and dead bodies, and resort in swarms to the situations in which they occur, either for the purpose of procuring food, or laying their eggs. Insects feed on a great variety of substances; there are few things, eithej in the vegetable or animal kingdom, whicl are not consumed by some of them. Tin leaves, flowers, fruit, and even the lignt, ous parts of vegetables, afford nourish ment to a very numerous class; anima* bodies, both dead and alive, even maw himself, is preyed on by many of them. several species of the louse, of the acarus, of the gnat, and the common flea, draw their nourishment from the surface of his body; the pulex ulcerans penetrates the cuticle, and even enters his flesh. A spe cies of gadfly (oestrus hominis) deposits itsto different cavities of his body. All the inferior animals have their peculiar parasitical insects, which feed on them during their life. There are some insects which can feed only on one species. Many caterpillars, both of moths and butterflies, feed on the leaves of some particular vegetable, and would die, could they not obtain this. There are others which can make use of two or three kinds of vegetables, but which never attain full perfection, except when they are fed on one particular kind ; for example, the common silkworm eats readily all the species of mulberry, and even common lettuce, but attains its greatest size, and produces most silk, when fed on the white mulberry. There are a great many which feed indiscriminately on a variety of vegetables. Almost all herbivorous insects eat a great deal, and very frequently; and most of them perish, if deprived of food but for a short time. Carnivorous insects can live a long while without food, as the carabus, ditiscus, &c. As many insects cannot transport themselves easily, in quest cf food, to places at a distance from one another, nature has furnished the perfect insects of many species with an instinct, which leads them to deposit their eggs in situations where the larvae, as soon as hatched, may find that kind of food which is best adapted to their nature. Most of the butterflies, though they flutter about, and collect the nectareous juice of a variety of flowers, as food for themselves, always deposit their eggs on or near to those vegetables which are destined, by nature, to become the food of their larvae. The various species of ichneumon deposit their eggs in the bodies of those insects on which their larvae feed. (See Ichneumon.) The sirex and sphex are likewise careful to deposit their eggs in situations where their larvae, when hatched, may find subsistence. The sphex figulus deposits its eggs on the bodies of spiders which it has killed, and enclosed in a cell composed of clay. Some insects, at different periods of their existence, make use of aliment of very different properties; the larvae of some are carnivorous, while the perfect insect feeds on the nectareous juice of flowers, e. g. sirex, ichneumon, &c. The iarvse of most of the iepidopterous insects feed on the leaves and young shoots of vegetables, while the perfect insects either take no food at all, or subsist on the sweet juice which they extract from flowers: indeed, the construction of their mouths functions of insects, beginning with respiration, which is the act of inhaling and exhaling the air into and out of the lungs. Mammalia, birds, and most of the amphibia, breathe through the mouth and fi nostrils. The air, when received into the lungs, is mixed with the blood, and imparts to it something necessary, and carries off something noxious. Some authors have asserted that insects have no lungs; but later experiments and observations show that no species is without them, or, at least, something similar to them; and, in many insects, they are larger in proportion to their bodies than in other animals. In most of them, they lie at or near the surface of the body, and send out lateral pores or tracheae. The respiration of insects has attracted the attention of many naturalists; and it is found that insects do not breathe through the mouth or nostrils; that there are a number of vessels, for the reception of air, placed along on each side of the body, commonly called spiracula, which are subdivided into a number of smaller vessels, or bronchise; that the vessels, or tracheae, which proceed from the.. pores on the sides, are not composed of a simple membrane, but are tubes formed of circular rugae; that the spiracula are distinguishable, and are covered with a small scaly plate, with an opening in the middle like a buttonhole, which is furnished with membranes, or threads, to prevent the admission of extraneous bodies. Insects are the only animals without vertebrae, in which the sexes are distinguished. Copulation is performed in them by the introduction of the parts of generation of the male into those of the female. All insects are either male or female, except in a few of the genera of the order hymenoptera, such as the bee, ant, &c, where individuals are to be found, which are neither male nor fe male, and, on that account, called neuters Among the bees, the neuters form the far greater part of the community, and perform the office of laborers. Among the ants, the neuters are very numerous, and constitute the only active members of the society. It has been alleged, that these neuters are nothing but females, whose parts have not been developed for want of proper nourishment. Oliver, however, after strict examination, is disposed to think them really different, though he does not adduce facts sufficient to establish his opinion. The parts which dis tiiiguish the male from the female may be divided into two classes, viz., 1. those which are not directly connected with generation ; 2. those which are absolutely necessary for the purposes of generation. The circumstances which have no direct communication with generation, which serve to point out the distinction between the sexes, are the difference of size observable in the male and female; the brightness of the color in each; the form and number of articulations of the antennae ; the size and form of their wings; the presence or absence of a sting. The male is always smaller than the female; the female ant is nearly six times larger than the male: the female cochineal is from 12 to 15 times the size of the male ; the female termes is 200 or 300 times the size of the male; the colors of the male are commonly much more brilliant than those of the female; this is particularly the case in lepidopterous insects; in some insects, the color of the male is totally different from that of the female: the antenna3 of the male are commonly of a different form, and larger than those of the female : frequently the males are furnished with wings, while the females have none ; the lampyris, coccus and blatta, and several moths, afford an example of this: the female bee is furnished with a sting, while the male is destitute of one: the males of some insects are furnished with sharp, prominent points, resembling horns, situated either on the head or breast, which are either not perceptible, or very faintly marked, in the female. The parts essential to generation afford the best distinguishing mark; in most insects, they are situated near the extremity of the rectum ; by pressing the abdomen near to the anus, they may frequently be made to protrude; but the parts of generation are not always situated near the anus; in the spiders, they are situated in the feelers ; in the libellula, the male organ is situated in the breast, while that of the* female is placed at the anus. The eggs of insects are of two sorts; the first membranaceous, like the eggs of the tortoise and the other reptiles; the other covered with a shell, like those of the birds. Their figure varies exceedingly ; some are round, some elliptical, some lenticmar, some cylindrical, some pyramidal, some flat, some square; but the round and oval are the most common. The eggb of insects seldom increase in size, from the time they have been deposited by the parent till they are hatched : those of the tenthredo, however, and of some others^ are observed to increase in bulk.At first, there is nothing to be perceived in the eggs of insects but a watery fluid , after some little time, an obscure point is observable in the centre, which, according to Swammerdam, is not the insect itself but only its head, which first acquires consistence and color ; and the same author alleges, that insects do not increase in bulk in the egg, but that their parts only acquire shape and consistence. Under the shell of the egg, there is a thin and very delicate pellicle, in which the insect is enveloped, which may be compared to the chorion and amnios, which surround the foetus in quadrupeds. The little insect remains in the egg till the fluids are dissipated, and till its limbs have acquired strength to break the egg and make its escape; the different species of insects remain enclosed in the egg for very different periods; some continue enclosed only a few days, others remain for several months. The eggs of many insects remain without being hatched during the whole winter, and the young insects do not come forth from them till the season at which the leaves of the vegetables, on which they feed, begin to expand. When the insects are ready to break their prison, they commonly attempt to pierce the shell with their teeth, and form a circular hole, through which they put forth first one leg, and then another, till they extricate themselves entirely. Insects afford nourishment to a great number of the superior animals; many of the fishes, reptiles and birds, draw the principal part of their sustenance from that source. The immense swarms of different species of crab, which abound in every sea, directly or indirectly form the principal part of the food of the cod, haddock, herring, and a great variety of fishes. The snake, lizard, frog, and many other reptiles, feed both on land and aquatic insects. Gallinaceous fowls, and many of the small birds, &c, feed on insects. Swallows, indeed, feed entirely on winged insects. They afford food, likewise, to many of the mammalia, viz., to many species of the bat, to the anteater, &c, and even to man himself. Many species of crab, viz., lobster, common crab, shrimp, prawn, landcrab, &c, are reckoned delicacies. The larvse of some coleopterous insects and locusts form part of the food of man. Insects, likewise, by consuming decayed animal and vegetable matter, which, if left to undergo the putre factive process on the surface of the ground, might taint the atmosphere with pestilential vapors, preserve the air pure for the respiration of man and other ani wals. On the other hand, the injuries which they inflict upon us are extensive and complicated; and the remedies which we attempt, are often aggravations of the evil, because they are directed by an ignorance of ths economy of nature. The little knowledge which we have of the modes by which insects may be impeded in their destruction of much that is valuable to us, has probably proceeded from our contempt of their individual insignificance. The security of property has ceased to be endangered by quadrupeds of prey, and yet our gardens are ravaged by aphides and caterpillars. It is somewhat startling, to affirm that the condition of the human race is seriously injured by these petty annoyances ; but it is perfectly true, that the art and. industry of man have not yet been able to overcome the collec tive force, the individual perseverance, and the complicated machinery of destruction which insects employ. A small ant, according to a most careful and philosophical observer (Humboldt), opposes almost invincible obstacles to the progress of civilization in many parts of the equinoctial zone. These animals devour paper and parchment; they destroy every book and manuscript. Many provinces of Spanish America cannot, in consequence, show a written document of a hundred years' existence. " What developement," he adds, "can the civilization of a people assume, if there be nothing to connect the present with the past; if the depositories of human knowledge must be constantly renewed ; if the monuments of genius and wisdom cannot be transmitted to posterity ?" Again, there are beetles which deposit their larvae in trees, in such formidable numbers, that whole forests perish beyond the power of remedy. The pines of the Hartz have thus been destroyed to an enormous extent; and at one place in South Carolina, at least 90 trees in every 100, upon a tract of 2000 acres, were swept away by a small, black, winged bug. Wilson, the historian of American birds, speaking of the labors of the ivorybilled woodpecker, says, " Would it be believed that the larvse of an insect, or fly, no larger than a grain of rice, should silently, and in one season, destroy some thousand acres of pine trees, many of them from two to three feet in diameter, and 150 feet high ? In some places, the whole woods, as far as you can see around you, are dead, stripped of the bark, their wintrylooking arms and bare trunks bleaching in the sun, and tumbling in ruins before every blast." The subterraneous larvee of a species of beetle has often caused a complete failure of the seedcorn, as in the district of Halle in 1812. The cornweevil, which extracts the flour from grain, leaving the husk be, hind, will destroy the contents of the largest storehouses in a very short period. The wireworm and the turnipfly are dreaded by every farmer. The ravages of the locust are too well known not to be at once recollected, as an example of the formidable collective power of the insect race. The white ants of tropical countries sweep away whole villages, with as much certainty as a fire or an inundation; ships even have been destroyed by these indefatigable republics, and the docks and embankments of Europe have been threatened by such minute ravagers. INSOLVENCY, (See Bankrupt) INSTANCE. On the European continent, a court is said to be of the first instance, when it has original jurisdiction of a case; of the second instance, when it has appellate jurisdiction from a lower court; of the third instance, when it has appellate jurisdiction from courts of the second instance. In some cases, generally criminal, a court may be of the first or second instance, according to the place where the process was begun; for instance, if a man is tried in Prussia for a high crime, and found guilty, he appeals, and the case is sent to another criminal court, chosen by the government, which, in this case, is of the second instance' while, in the next case, perhaps, the situation of the two courts may be reversed. To absolve ah insiantia means to absolve a person from an accusation, without carrying through the process..