Part 32

Every one has heard of the destructive as well as constructive qualities of the "White Ant;" another quotation from Kirby and Spence will illustrate both.

"When they find their way into houses or warehouses nothing less hard than metal or glass escapes their ravages; their favourite food, however, is wood of all kinds, except the Teak, and Ironwood, which are the only sorts known, that they will not touch; and so infinite are the multitudes of the assailants, and such is the excellence of their tools, that all the timber-work of a spacious apartment is often destroyed by them in a few nights. Exteriorly, however, everything appears as if untouched; for these wary depredators (and this is what constitutes the greatest singularity of their history) carry on all their operations by sap and mine, destroying utterly the inside of solid substances, and scarcely ever attacking their outside until they have first concealed it and their operations with a coating of clay. A general similarity runs through the proceedings of the whole tribe, but the large African species, called by Smeathman Termes bellicosus, is the most formidable. These insects live in large clay nests, from whence they excavate tunnels all round, often to the extent of several hundred feet; from these they will descend a considerable depth below the foundation of a house, and rise again through the floors; or, boring through the posts and supports of the building, enter the roof and construct their galleries in various directions.

"If a post be a convenient path to the roof, or has any weight to support, (how they discover it is not easily conjectured), they will fill it with their mortar, leaving only a track-way for themselves, and thus, as it were, convert it from wood into stone as hard as many kinds of freestone. In this manner they soon destroy houses, and sometimes whole villages, when deserted by their inhabitants, so that in two or three years not a vestige of them will remain. These insidious insects are not less expeditious in destroying the wainscoating, shelves, and other fixtures of a house, than the house itself; with the most consummate art and skill they eat away the inside of what they attack, except a few fibres here and there, which exactly suffice to keep the two sides, or top and bottom, connected, so as to retain the appearance of solidity after the reality is gone; and all the while they carefully avoid perforating the surface, unless a book or any other thing that tempts them should be standing upon it.

"Koempfer, speaking of the White Ants of Japan, gives a remarkable instance of the rapidity with which these miners proceed. Upon rising one morning he observed that one of their galleries of the thickness of his little finger had been formed across his table; and upon a further examination he found that they had bored a passage of that thickness up one foot of the table, formed a gallery across it, and then pierced down another foot into the floor; all this was done in the few hours that intervened between his retiring to rest and his rising."

Most of this order are armed with some weapon of defence. The Bee and Wasp have each a most formidable sting, with which they are able to inflict a wound fatal to most insects. The Ants have a peculiar secretion, consisting of formic acid, which they eject with great force, and which has a very disagreeable smell. The eggs of Ants when hatched produce a small grub, which spins itself a sort of cocoon, and in this state it so much resembles a grain of corn, that it has been mistaken for it; this error has given rise to the supposition that Ants store up corn for winter, whereas they never eat corn, but the care they take of these larvæ, removing them from place to place, taking them up in their mandibles and running along with them, has been mistaken for the act of storing away grains of corn.

5. STREPSIPTERA (Twisted-winged).

This order includes but a few species; Dr. Baird in his Cyclopædia, gives the following account of them:--

"Certain insects were discovered by Kirby, living parasitic in the abdomen of some Andrenæ, which at that time were nondescript, and could not be referred to any existing order. They were afterwards placed in an order by themselves, which he called Strepsiptera. The larvæ live in the bodies of Bees, Wasps &c., and the males only undergo a perfect metamorphosis; the females, even when adult, have neither legs, wings, nor eyes, but resemble larvæ, and continue to live parasitic in the bodies of the Hymenopterous insects within which they were born. The characters are thus taken from the male and consist chiefly in the structure of the wings. The anterior pair are quite rudimentary, being transformed into a pair of short, slender, contorted appendages resembling narrow balancers or halters. The posterior pair are large and membraneous, their nervures are only longitudinal, so that they are able to fold them like a fan. They have large globular eyes, with the facets few, but of comparatively large size."

About ten or twelve species are known, forming a small family, "Stylopidæ." The genus Stylops may be taken as the type, and contain such species as have the tarsi with four points and the antennæ with six."

6. LEPIDOPTERA (Scaly-winged).

This order includes the Butterflies and Moths, they have four wings, which are large and covered with minute scales, which are for the most part of a heart or battledore shape, as in fig. 27. The wings of these insects are many of them beautifully marked and tinged. There are about 12,000 species, by some divided into "diurnal" (or those which fly by day), "crepuscular" (or those which fly in the evening), and "nocturnal" (or those flying by night). The Moths are mostly crepuscular and nocturnal, while the Butterflies are chiefly diurnal, but the most usual distinction between the Moth and Butterfly consists in the form of the antennæ, those of the Moth being feather-shaped, while those of the Butterfly have a small knob at the end, or, as it is called, "club-shaped." The Lepidoptera feed upon the nectar of flowers, for which purpose they are furnished with a long proboscis or "Haustellium," which is curled up under the head, it consists of two semi-cylindrical pieces which when placed side by side form a tube, up which the nectar is drawn by capillary attraction. The metamorphosis of these insects is complete.

The Silkworm (Bombyx mori) belongs to this order. It is the most important of all insects to man, as from it alone all the silk of commerce is obtained. Its cocoon is of a beautiful yellow colour, varying in shade from orange to pale straw-colour; the silk of one cocoon weighs somewhere about three grains; it would therefore, at this calculation, take 1920 worms to spin one pound. The annual import of silk into this country alone is about 7,000,000 pounds, it must therefore take 13,440,000,000 Silkworms to supply us with silk yearly! The Silkworm feeds almost exclusively on the leaves of the mulberry.

7. HEMIPTERA (Half-winged).

The Hemiptera have two pairs of wings, the hindermost small, and the foremost pair half horny and half membraneous, the base being horny, and the apex membraneous. They include the Bugs, some of which are aquatic, as the Water Scorpion (Nepa), and the Water Boatman (Natonecta), which swims on its back, rowing itself by means of a pair of long legs, which look like oars; the common bed Bug is also of this order, although wingless, as are also the Plant Lice (Aphides), which, however, obtain wings in their perfect state.

8. DIPTERA (Two-winged).

The Diptera include the common House Fly (fig. 16), Bluebottle Fly, Gnat, and many others; their wings are like the Neuroptera, but they have but one pair, the other pair being undeveloped, form little knobs called "balancers." The wings of Flies are generally covered with short stout hairs, as seen in fig. 29; the common Fly feeds upon almost anything, but some of the Diptera feed exclusively on the blood of other animals; the Gnat (Culex pipiens), of which the Mosquito is a variety, deposits its egg in the water on any floating substance, the larva which comes from the egg is aquatic, living with its head downwards, the end of the abdomen only being above the water, in this there is a spiracle or breathing orifice, which enables it to take in the air; the Gnat, when it comes from this larva, stands on its shell for a moment, and then flies off, for it is not suited to live in the water; this history of the early stages of its life, accounts for Gnats being always found in such numbers near pools of water. The Tsetse, which Dr. Livingstone describes as being so fatal to cattle, is of this order; he says, "It is well known that the bite of this poisonous insect is certain death to ox, horse, or dog.... A most remarkable feature in the bite of the Tsetse is its perfect harmlessness to man and wild animals, and even calves, so long as they continue to suck the cows."

9. APTERA (Wingless).

To this order belongs the Flea (Pulex irritans), which is furnished with lancet-shaped weapons, through which it sucks the blood of other animals, for it is entirely parasitic, and also the "Chigeo" (Pulex penetrans), which is a troublesome and even dangerous pest in the West Indies; it penetrates the skin of the feet, and deposits its young beneath it.

The last class of the Articulata, the Arachnida, includes the Spiders, Scorpions, Centipedes, and Millipedes. The Arachnida differ from insects, in having eight or more legs, more than two eyes, no wings, and no head; the Spiders have four pairs of legs, and six, eight, or more, simple eyes, which appear as minute spots on the upper part of the thorax. Spiders nearly all live by preying upon small insects, which they catch in several ways, but by far the most general mode is by constructing a web or net to entangle them; the threads of this web are made of a fluid glutinous substance, which is secreted within the abdomen, and which they project from extremely minute orifices, several of which exist on the point of little projections called "spinnarets," this liquid dries into a solid thread immediately it comes into contact with the air; it is extremely strong, and so fine that several thousand of the single fibres will only make the size of a human hair. The Garden Spider (Epeira diadema) is often called the Geometrical Spider, from the regularity of its web. These Spiders will often place a thread from one spot to another, where it would seem impossible that they could attach it, such as from the branch of a tree to the corner of a house twenty feet or more from the ground; it has never been accurately determined how the Spider does this, and it is the more difficult to observe, as it is always done in the night, but it has been supposed that a fine thread is spun, and that the wind carries it across, when it is strengthened and afterwards made tight. The Spider (Araneæ domestica) that makes "cobwebs" in the corners of rooms, is called the Weaving Spider. Some Spiders are called Hunting Spiders, they do not construct webs, but pounce upon their prey with a leap; the Mygale avicularis of South America is one of this kind; it is said that some grow so large that their feet spread out a foot wide. The Long-legged Spider, often found in our houses, and of which fig. 32 is an exact copy, measures 3 1/2 inches, and is the largest species we have. There are also aquatic Spiders, which feed upon insects in the water and dive down for them; their surface being hairy and unctuous, retains sufficient air to bring them up and prevent them being wetted. The eyes of Spiders are different from those of other insects; they appear as simple, shining spots, or "ocelli," and not compound eyes, having a great many "ocelli" compounded into one. These "ocelli" are arranged in a group of eight or more, and placed on the upper part of the thorax, for Spiders have no head, although generally represented with one. The eggs of Spiders are generally deposited in some sheltered place, fastened together and partly covered with a net-work of a sort of yellow silk, very much resembling the cocoon of the Silkworm. The Scorpion, so terrible in appearance, and in its sting so deadly, and which is sometimes a foot in length, belongs to this order. It has eight legs, and a pair of claws like a lobster, the body is lengthened into a sort of tail, at the end of which is a claw or sting, like the poison fang of a serpent, with a poison bag at its root; its effects are often fatal to man, and always so to the insects and other small animals upon which the Scorpion feeds, its usual mode of killing which, is to catch them with its claws and then to sting them to death. The Centipede is a scarcely less frightful creature; in South America and the West Indies it is sometimes found to grow to eight or ten inches in length, it is of a long jointed form, with generally twenty-one pairs of legs, although some have double this number; its bite is much to be dreaded, as it is poisonous, especially the "Scolopendræ," which have a poison gland, like the snake; in this country they are very small indeed, and are generally found in moist places.

The Centipedes and Millipedes are, by some, placed in the class Arachnida, but by others in a separate class called "Myriopoda," divided into two orders, the Chilognatha, which have rounded cylindrical bodies, and generally more than one pair of legs to each segment of the body, and the Chilopoda, which have a distinct flattened head and but one pair of legs to each segment.

1, Nautilus (Argonauta); 2, Clio Borealis; 3, Mussel (Mytilus edule).]

The last of the three great divisions of the Invertebrata is formed by the Mollusca; it is divided into six classes, (see page 218). The Mollusca are characterised by having no internal skeleton, nor external horny case, as in the Articulata; they are rather soft, and either void of solid covering, or possessed of "shells" composed chiefly of earthy matter (chalk), and in one or two pieces, called valves, hence the names, uni-valve and bi-valve; all shells of this description belong to the Mollusca, some of which have no means of locomotion, as Oysters; others have a "foot" covered with a muscular expansion, called the "mantle," by which they glide onwards, as the Snail.

1. The Tunicata have no shell or hard covering, but are of a pretty firm consistence; they are either fixed to rocks and sea-weeds, or float about freely, and are either solitary, social, or compound. The "Ascidians" are united in groups, and are all connected by a common stalk or "Stolon," from which they grow by buds.

2. The Brachiopoda. These Molluscs are furnished with a pair of shells, within which the animal lives; one of these shells (the ventral one) has a small hole in it, close to the hinge, and through this a long tendinous cord passes, which fixes the creature to some stone or rock, hence the name Brachiopodous, which means arm-footed. The young of this Mollusc are not fixed, but float about. The Lingula has horny shells, and the foot passes out between them; these creatures were some of the first created, if not the very first; the shells of Terebratula are found in vast quantities in the oldest fossiliferous strata.

3. The Lamellibranchiata include a great many of our most ordinary Mollusca, commonly known as "shell fish." They have a pair of shells, and are thence called "bivalve." The Oyster (Ostrea edulis), Mussel (Mytilus edulis), Cockle (Cardium edule), Scallop (Pecten), belong to this class. Oysters form a considerable article of commerce, thirty or forty thousand bushels are brought each season to London; they are dredged up from "beds," where they are found in great quantities. They spawn in May and June, and are not then good. There is an old and a well-known saying, that "Oysters are not fit to eat, unless there is an R in the month," all the names of the months containing an R but May, June, July, and August. The spawn is collected and placed in artificial beds, consisting of shallow places or hollows in the sea, where the tide will not wash them away, and whence they can be easily removed when sufficiently grown, which is in five or six years; these creatures have no powers of locomotion, but remain where the tide washes them; but Scallops, Cockles (fig. 34), and Mussels (fig. 33), have the power of fixing themselves to any substance they wish, by means of the "byssus" or beard, which is a tuft of fibres passing out from between the shells; and it is said, the Scallops have the power of progression, by suddenly opening and shutting the shells.

4. The Pteropoda are Mollusca which have no shell, or a very thin one; the Clio borealis (fig. 33), which forms the chief food of the Whale, is found in great multitudes in the Arctic seas, it swims about by means of two extensions, similar to wings. The Hyaloea has a small round transparent shell.

5. The Gasteropoda are extremely numerous; most of them have univalve shells, but many of them have none, as the Garden Slug (Limax, fig. 35). The Whelk (Buccinum undatum), Perriwinkle (Littorina littoria), Garden Snail (Helix aspersa, fig. 35), and the Wentle-trap (Scalaria, fig. 36), are the most familiar examples of this class. These Mollusca walk by means of the mantle, which is muscular, and capable of alternate contraction and expansion; they breathe by means of lungs on their back beneath the shell, and to which there is an opening in their side. What are usually called the horns are four in number, two short and two long; they are tentaculæ, but what is peculiar in them is the circumstance of having the eyes placed at their ends. These Mollusca have a sort of valve, which, when they retire into the shell, closes it like a lid; it is called the "Operculum;" in some cases it is horny, as in the Perriwinkle, and in others, resembles shell; the shells of these mollusca are coiled into a spiral, this is caused by the shell always growing by additions to the edges of the mouth, and in nearly every case this spiral turns in the same direction that a screw does, but in a very few it turns in the opposite direction, as in the "Fusus contrarius."

6. The Cephalopoda include the "Cuttle-Fish," and Nautilus (fig. 33). They are furnished with eight or ten tentacula or arms, which spring from the head, and which are covered with suckers; the mouth is in the centre, and these tentacula are used to lay hold of their prey and convey it to the mouth; they have two perfect eyes, and they breathe by gills. The Nautilus has a univalve shell, which is of a very graceful and elegant form; its interior is divided into chambers, with a syphon running through them, by which the air is exhausted or compressed so as to cause them to sink or swim; the animal occupies only the outer chamber; the extinct Ammonite belonged to this class. It is from the Cuttle-Fish (Sepiæ) that the beautiful dark brown pigment, known as "sepia," is obtained, and also the material of which Indian-ink is made.