Part 31

The Crustacea form the third class of the Articulata, they comprise animals covered with a hard shell or carapace, like a case made up of rings, with joints allowing the pieces to move upon each other, except where several of them are consolidated to form the principal covering. These rings generally amount to twenty-one in number, some composing the claws, others the legs, &c. The shell is chiefly made of carbonate of lime (chalk) held together by animal matter. The greater part of the Crustacea inhabit the waters, and they cast their shells from time to time as they grow; the Lobster (Astacus marinus), is a familiar example, it is found in the sea near rocky shores, and is capable of rapid motion under the water, darting along (tail foremost) with great rapidity, it has powerful claws, with one of which (the blunt one) it holds its food and with the other (the sharp one) cuts it up into pieces; they have the power of casting off these claws and reproducing them; they feed upon smaller Crustacea and fish, or any animal matter they can find. The Cray-fish is another example, it is a sort of fresh-water Lobster, living in holes (frequently deserted rat holes) in the banks of rivers; its shell is very rough, but otherwise somewhat resembles the Lobster. Crabs, Shrimps, and Prawns, are members of this class (fig. 15).

1. Lobster (Astacus marinus). 2. Cray-fish (Astacus fluviatilis). 3. Crab (Cancer pagurus). 4. Shrimp (Crangou vulgaris). 5. Prawn (Palæmon serratus). ]

1. Dragon-fly (Libellulina depressa). 2. Grasshopper (Gryllus). 3. Bee (Apis mellifica). 4. Fly (Musca domestica). 5. Butterfly (Pontia brassicæ). 6. Musk-beetle (Cerambyx moschatus). ]

The Insects form the fourth class of this division, and by far the most important and numerous. They come to maturity only after undergoing successive changes from the egg to the perfect animal; these transformations are amongst the most wonderful things connected with them. The eggs (some of which are very beautiful) are first deposited in some safe place, either attached to a leaf or tied up in a small bundle by silken threads spun by the parent insect, and in some nutritious substance, so that when it comes to life it may at once have food; this is sometimes in manure, sometimes in flesh, and sometimes under the skin of a living animal (few are exempt from this infliction), where they remain for a time and then come forth as maggots, caterpillars, &c.; in this state they are called "larvæ," these are generally active creatures and eat most voraciously, which seems to be the principal act of this state of their existence. These larvæ frequently change their skins as they grow, and at last they assume the next stage of their life, the pupa or chrysalis state, which is one generally of complete inactivity; many of these larvæ, weave themselves a covering of a sort of silk, to defend them while in the pupa state--such as the Silkworm, whose covering (cocoon) is the source of all the silk of commerce--others merely place themselves in a situation of security. The pupa remains dormant for a certain time, and then becomes the imago or perfect insect (the last state of its existence), such as a Moth, a Butterfly, a Beetle, &c. These are of different sexes, and in due time produce a batch of eggs and then die; these eggs are often incredible in numbers, amounting to many thousands--fortunately but few escape the watchful eyes of other insects and of birds who feed upon them.

Insects have six jointed legs, a pair of antennæ or horns (as they are called) and generally one or two pairs of wings. The head is joined to the body by a constricted neck, the part of the body to which it is joined is called the thorax, and to this is added the posterior part or abdomen; this part is extremely various in form in different insects, in some it is round and full, in others long and extended. The antennæ arise from the head, and are generally composed of eleven pieces variously disposed; these wonderful organs are possessed of great sensibility, and they certainly serve to convey information to the insect, of the nature of one of the special senses; it was formerly thought to be simply that of touch very much refined, or of smell, but it is now generally considered to be that of hearing, or a modification of it. The forms of the antennæ are very various, fig. 17 represents that of the Cockchaffer (Melolontha vulgaris). The legs proceed from the thorax, as do the wings, the abdomen giving rise to none of the extremities; the feet of insects are all pretty much upon the same model, some being more developed than others, they have a pair of hooks or claws for catching and clinging to rough surfaces, and a pair of cushions or pads, covered in some cases with suckers. The foot of the Fly (fig. 18) is well developed in this particular, enabling it to walk with perfect ease even on glass or the smoothest surface, and in any position. Insects do not breathe by lungs or gills, but by means of branched tubes called "tracheæ," which convey the air to the interior of the animal. On the surface of these, the blood vessels ramify, giving out the carbonic acid of the blood and receiving oxygen; the openings to these air-tubes are arranged along the sides of the body, and are called "spiracles" (fig. 19). They are curious objects under the microscope, some of them being closed by a perforated membrane, others have a sort of sieve or network of fibres, and most of them a contrivance to catch and exclude minute particles of matter floating in the air, and thus prevent their entry into the tracheæ. Insects have two eyes, one on each side of the head, which are of great size, often forming complete hemispheres; each eye is made up of several thousand separate eyes or "ocelli," hence they are called compound eyes; these ocelli are placed closely together, so as to form a sort of honeycomb arrangement; the appearance of a part of one of these eyes is shown in fig. 20.

(1, perpendicular section; 2, surface.)]

Insects are amongst the most active of creatures, whether for good or for evil, and the prodigious rapidity with which they increase under favourable circumstances would soon cause them to overrun the whole earth, to the extinction of almost every other creature, were these circumstances not controlled by an all-wise Providence, who keeps a constant check upon their progress by causing one insect to feed upon another, and who has formed almost innumerable other creatures (including birds, reptiles, and fishes) with instincts which lead them to feed upon insects in every stage of their development (fish devour the larvæ of many insects which inhabit the waters during the first stage of their existence); but it occasionally happens, when some of these salutary checks upon their increase are withdrawn, that they multiply with such fearful rapidity as to produce a complete famine, for they eat up everything before them. Who has not heard of the plagues of Locusts and the depredations of the White Ants? The swarms of Locusts in Africa will sometimes cover many hundred square miles of surface, and in this space not a vestige of any vegetation would remain after their visit. The description of the prophet Joel is sublime: "The land is as the garden of Eden before them, and behind them a desolate wilderness: yea, and nothing shall escape them.... The earth shall quake before them, the heavens shall tremble: the sun and the moon shall be dark, and the stars shall withdraw their shining."

But it is kindly ordained that these visitations shall only occasionally take place, and even when they do, terrible as is the infliction, a benefit in reality outweighing the injury often succeeds; for the land in these countries is often made almost barren by the quantities of tangled roots and stubble on the surface of the earth, which by the destructive powers of these insects is completely removed, and their manure left in its place, so that the fertility of the ground is much increased (often tenfold) after their visits.

The thousands of species of insects which exist, render it impossible in a work like this, even to name them, but under the separate orders will be given a slight outline of the more important.

Insects are divided, according to the character of their wings, into nine orders.

1. COLEOPTERA (Black-winged).

The Coleoptera are those insects generally denominated Beetles, they have four wings, the two outer of which are not used to fly with, but as cases to cover and protect the other two; they are called "elytra," are horny and firm in texture, and in some cases, as the Diamond Beetle and Musk Beetle, beautifully ornamented; the under pair of wings fold transversely so as to pack up under the outer ones, which are shorter. All Beetles live but one season, both sexes die before winter, leaving nothing but their eggs to continue the species, the larvæ which come from these are very destructive, eating most voraciously; for the most part, Beetles feed on decaying substances such as dung, &c., and are therefore useful creatures; there are between 40,000 and 50,000 species of them. Beetles have been called the scavengers of nature, and truly they are so, for they (with other insects) clear off all dead matter, whether animal or vegetable; the Geotrupes stercorarius, and others, dig holes in the ground and bury the excrement which is deposited on the surface, thus doing a great service to vegetation, taking it down to nourish the roots of the grass and other plants instead of allowing it to harden and decompose on the surface. All dead animals are at once attacked and devoured by insects, and the Beetles play their full share in this necessary operation.

There are certain Beetles, called Burying Beetles (Necrophorus vespillo), which remove the earth from under the dead bodies of small animals, such as birds or mice, till they are beneath the level of the ground, when they cover them up and deposit their eggs in them; these bodies form stores of food for the future larvæ.

The Stag Beetle (Lucanus cervus, fig. 22), the Dor Beetle (Geotrupes stercorarius), the Cockchaffer (Melolontha vulgaris), the Musk Beetle (Cerambyx moschatus, fig. 16), and the Lady-bird (Coccinella), are well-known members of this order.

2. ORTHOPTERA (Straight-winged).

The Orthoptera are those insects whose wings fold longitudinally; they have two pairs, but the anterior pair are horny and serve as wing-cases to the posterior pair; their food is chiefly vegetable, but to many of their species any kind is acceptable, as their mouths are suitable for grinding-up hard substances. The Locusts (Locustidæ, fig. 21), Grasshoppers (Gryllidæ), Crickets (Achetidæ, fig. 16), and Cockroaches (Blattidæ), or Black-beetles, as they are sometimes incorrectly called, belong to this tribe. Their metamorphoses are not so complete as in many other insects, for they never entirely change their form; the larva as it leaves the egg has no wings, but otherwise is much like the parent; it changes its skin several times, which stage is analogous to the pupa state, after casting it five times and obtaining wings, it becomes the imago or perfect insect. The ravages of the Locusts are so well known that little need be said; the following is from Kirby and Spence's Entomology:--

"Although this animal be not very tremendous for its size, nor very terrific in its appearance, it is the very same whose ravages have been the theme of naturalists and historians in all ages, and upon a close examination you will find it to be peculiarly fitted and furnished for the execution of its office. It is armed with two pairs of very strong jaws, the upper terminating in short, and the lower in long teeth, by which it can both lacerate and grind its food; its stomach is of extraordinary capacity and powers; its hind legs enable it to leap to a considerable distance, and its ample vans are calculated to catch the wind as sails, and so to carry it sometimes over the sea; and although a single individual can effect but little evil, yet when the entire surface of a country is covered by them, and every one makes bare the spot on which it stands, the mischief produced may be as infinite as their numbers. So well do the Arabians know their power, that they make a Locust say to Mahomet, 'We are the army of the Great God; we produce ninety-nine eggs; if the hundred were completed, we should consume the whole earth and all that is in it.'"

3. NEUROPTERA (Nerve-winged).

The Neuroptera comprise the Dragon-fly (Libellulina, fig. 16), Ant-lion (Myrmelion), Caddis-flies (Phryganidæ), and the May-flies (Ephemera); these insects have wings of a beautiful network structure, as may be seen in the Dragon-fly, they make their appearance about the middle of June in the locality of ditches and ponds. The Caddis-fly is noted for the peculiar case which the larva makes for itself; the larva inhabits the water and the ease is made of little fragments of wood, shell, and sand, agglutinated together so as to float; the perfect insect is not aquatic, and flies away when formed. The May-flies are noted for the shortness of their existence, the larvæ live in the water, and many of them are eaten by fishes who are very fond of them, but sufficient numbers come to the perfect state, to form complete clouds in the air where the larvæ were, these creatures live but a day, and some of their species but an hour or two, in the perfect state, they deposit their eggs in the water, which come to life in the mud at the bottom. The flight of these fragile beings and their short-lived holiday festivities are well described by Kirby and Spence:--

"In the beginning of September, for two successive years, I was so fortunate as to witness a spectacle of this kind, which afforded me a more sublime gratification than any work or exhibition of art has power to communicate. The first was in 1811. Taking an evening walk near my house, when the sun, declining fast towards the horizon, shone forth without a cloud, the whole atmosphere over and near the stream swarmed with infinite myriads of Ephemeræ and little gnats of the genus chironomus, which in the sun-beam appeared as numerous and more lucid than the drops of rain, as if the heavens were showering down brilliant gems. Afterwards, in the following year, one Sunday, a little before sunset, I was enjoying a stroll with a friend at a greater distance from the river, when in a field by the road-side the same pleasing scene was renewed, but in a style of still greater magnificence; for, from some cause in the atmosphere, the insects at a distance looked much larger than they really were. The choral dances consisted principally of Ephemeræ, but there were also some chironomi, the former, however, being most conspicuous, attracted our chief attention. Alternately rising and falling, in the full beam they appeared so transparent and glorious, that they scarcely resembled anything material; they reminded us of angels and glorified spirits drinking life and joy in the effulgence of the Divine favour. The Bard of Twickenham, from the terms in which his beautiful description of his sylphs is conceived in the 'Rape of the Lock' seems to have witnessed the pleasing scene here described:--

'Some to the sun their insect wings unfold, Waft on the breeze, or sink in clouds of gold; Transparent forms, too fine for mortal sight, Their fluid bodies half dissolved in light; Loose to the wind their airy garments flew, Thin glittering textures of the filmy dew, Dipt in the richest tincture of the skies, Where light disports in ever mingling dyes, While every beam new transient colours flings, Colours that change whene'er they wave their wings.'"

4. HYMENOPTERA (Membrane-winged).

The Hymenoptera are those insects which have four membraneous wings. The Bees (Apidæ, fig. 16), Wasps (Vespidæ), the Ants (Formicidæ), and the Ichneumon Flies (Ichneumonidæ), are the chief tribes of this order. The Bees, Wasps, and Ants are celebrated for forming societies, more perfectly arranged and governed than in any other creatures but man. It is curious that the most perfect instincts (such as approach so nearly to reason that they almost defy us to make a distinction) should have been given by the Creator to creatures so far removed from man in the scale of existence, and so little resembling him in any other particular. This is one of the stumbling-blocks in the way of those who wish to have it believed that all animals are progressive from certain types, which cannot be got over; if such were the case, man would be most nearly imitated by the Apes, and these again by those most nearly allied to them, and so on downwards, but here we find a government almost as perfect as that of the human species--an arrangement of work, a division of labour, buildings, storehouses, &c.--showing nearly all the social habits and feelings of man, in creatures who in form and size have no resemblance to him.

Kirby and Spence, in describing the societies of insects, say:--"But when we consider the object of these societies, the preservation and multiplication of the species, and the means by which that object is attained (the united labours and co-operation of perhaps millions of individuals), it seems as if they were impelled by passions very similar to those main-springs of human associations which I have just enumerated. Desire appears to stimulate them, love to allure them, fear to alarm them. They want a habitation to reside in and food for their subsistence. Does not this look as if desire were the operating cause which induces them to unite their labours to construct the one and provide the other? Their nest contains a numerous family of helpless brood. Does not love here seem to urge them to exemplary and fond attention, and those unremitted and indefatigable exertions manifested by the whole community for the benefit of these dear objects? Is it not also evident by their general and singular attachment to their families, by their mutual caresses, by their feeding each other, by their sympathy with suffering individuals and endeavours to relieve them, by their readiness to help those that are in difficulty, and finally by their sports and assemblies for relaxation? That fear produces its influences upon them seems no less evident, when we see them agitated by the approach of enemies, endeavour to repel their attacks, and to construct works of defence. They appear to have besides a common language, for they possess the faculty, by significative gestures and sounds, of communicating their wants and ideas to each other."

Numerous works have been entirely devoted to the habits and instincts of Bees and Ants, and very interesting they are, but it would be impossible to give an intelligible account of them in the small space allotted in this volume.

The wax of which Bees build their beautiful six-sided cells, and which is the whole source of all the wax used by men for a variety of purposes, is secreted in little scales or flakes, between the joints of the abdomen, from whence the wax-making Bees take it to build the comb; the cells of the comb are filled with honey, which is obtained by the Bees (by means of the apparatus shown at fig. 23), from the nectaries of flowers in the form of nectar, and is converted into honey in the honey-bag of the Bee, from whence it is discharged into the cells. Bees also collect the pollen from the flowers they visit, this adheres to the hairs on the Bee, and is scraped and brushed off, and collected into two little lots, which the Bee carries on each hind leg, this pollen is made into bee-bread. By scattering the pollen, flowers are often fecundated, for there are many plants, the female flowers of which are separate from the males, and it is only by insects and the wind, that the females are fecundated, for the Bee, with the pollen adhering to every part, first visits one flower and then another in search of nectar.

With respect to the Ants, Kirby and Spence give the following account of the building of their habitations,

"The nest of Formica brunnea is composed wholly of earth, and consists of a great number of stories, sometimes not fewer than forty, twenty below the level of the soil, and as many above, which last, following the slope of the ant-hill, are concentric. Each story, separately examined, exhibits cavities in the shape of saloons, narrower apartments, and long galleries which preserve the communication between both. The arched roofs of the most spacious rooms are supported by very thin walls, or occasionally by small pillars and true buttresses; some having only one entrance from above, others a second, communicating with the lower story; the main galleries, of which, in some places, several meet in one large saloon, communicate with other subterranean passages, which are often carried to the distance of several feet from the hill. These insects work chiefly after sunset. In building their nest they employ soft clay only, scraped from its bottom when sufficiently moistened by a shower, which, far from injuring, consolidates and strengthens their architecture. Different labourers convey small masses of this ductile material between their mandibles, and with the same instrument they spread and mould it to their will, the antennæ accompanying every movement. They render all firm by pressing the surface lightly with their fore feet; and however numerous the distinct masses of clay composing these walls, and though connected by no glutinous material, they appear when finished, one single layer, well united, consolidated and smoothed. Having traced the plan of their structure, by placing here and there the foundations of the pillars and partition-walls, they add successively new portions; and when the walls of a gallery or apartment, which are half a line thick, are elevated about half an inch in height, they join them by springing a flattish arch or roof from one side to the other. Nothing can be a more interesting spectacle than one of these cities while building. In one place vertical walls form the outline, which communicate with different corridors by openings made in the masonry; in another we see a true saloon, whose vaults are supported by numerous pillars; and further on are the cross-ways or squares where several streets meet, and whose roofs, though often more than two inches across, the Ants are under no difficulty in constructing, beginning the sides of the arch in the angle formed by two walls, and extending them by successive layers of clay till they meet; while crowds of masons arrive from all parts with their particles of mortar, and work with a regularity, harmony, and activity, which can never enough be admired. So assiduous are they in their operations, that they will complete a story with all its saloons, vaulted roofs, partitions and galleries, in seven or eight hours. If they begin a story, and for want of moisture are unable to finish it, they pull down again all the crumbling apartments that are not covered in."