Part 24

"The perfect cleanliness of these creatures is a very notable circumstance, when we consider that nearly their whole lives are passed in burrowing in the earth, and removing nuisances; yet such is the admirable polish of their coating and limbs, that we very seldom find any soil adhering to them. The meloe, and some of the scarabæi, upon first emerging from their winter's retreat, are commonly found with earth clinging to them; but the removal of this is one of the first operations of the creature; and all the beetle race, the chief occupation of which is crawling about the soil, and such dirty employs, are, notwithstanding, remarkable for the glossiness of their covering, and freedom from defilements of any kind. But purity of vesture seems to be a principal precept of Nature, and observable throughout creation. Fishes, from the nature of the element in which they reside, can contract but little impurity. Birds are unceasingly attentive to neatness and lustration of their plumage. All the slug race, though covered with slimy matter calculated to collect extraneous things, and reptiles, are perfectly free from soil. The fur and hair of beasts, in a state of liberty and health, is never filthy or sullied with dirt. Some birds roll themselves in dust, and, occasionally, particular beasts cover themselves with mire; but this is not from any liking or inclination for such things, but to free themselves from annoyances, or to prevent the bites of insects. Whether birds in preening, and beasts in dressing themselves, be directed by any instinctive faculty, we know not; but they evidently derive pleasure from the operation, and thus this feeling of enjoyment, even if the sole motive, becomes to them an essential source of comfort and of health."

The rose or green chafer (Cetonia aurata), which is one of our prettiest native insects, is one of the burrowers, and, for the purpose of depositing her eggs, digs, about the middle of June, into soft light ground. When she is seen at this operation, with her broad and delicate wings folded up in their shining green cases, speckled with white, it could hardly be imagined that she had but just descended from the air, or dropped down from some neighbouring rose.

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The proceedings of the Tumble-Dung Beetle of America (Scarabæus pilularius, Linn.) are described in a very interesting manner by Catesby, in his 'Carolina.' "I have," says he, "attentively admired their industry, and mutual assisting of each other in rolling their globular balls from the place where they made them to that of their interment, which is usually the distance of some yards, more or less. This they perform breech foremost, by raising their hind parts, and forcing along the ball with their hind feet. Two or three of them are sometimes engaged in trundling one ball, which, from meeting with impediments on account of the unevenness of the ground, is sometimes deserted by them. It is, however, attempted by others with success, unless it happens to roll into some deep hollow or chink, where they are constrained to leave it; but they continue their work by rolling off the next ball that comes in their way. None of them seem to know their own balls, but an equal care for the whole appears to affect all the community. They form these pellets while the dung remains moist, and leave them to harden in the sun before they attempt to roll them. In their moving of them from place to place, both they and the balls may frequently be seen tumbling about the little eminences that are in their way. They are not, however, easily discouraged; and, by repeating their attempts, usually surmount the difficulties."

He further informs us that they "find out their subsistence by the excellency of their noses, which direct them in their flight to newly-fallen dung, on which they immediately go to work, tempering it with a proper mixture of earth. So intent are they always upon their employment, that, though handled or otherwise interrupted, they are not to be deterred, but immediately, on being freed, persist in their work without any apprehension of danger. They are said to be so exceedingly strong and active as to move about, with the greatest ease, things that are many times their own weight. Dr. Brichell was supping one evening in a planter's house of North Carolina, when two of them were conveyed, without his knowledge, under the candlesticks. A few blows were struck on the table, and, to his great surprise, the candlesticks began to move about, apparently without any agency; and his surprise was not much lessened when, on taking one of them up, he discovered that it was only a chafer that moved it."

We have often found the necklace-beetle (Carabus monilis) inhabiting a chamber dug out in the earth of a garden, just sufficient to contain its body, and carefully smoothed and polished. From the form of this little nest, it would seem as if it were constructed, not by digging out the earth and removing it, but chiefly by the insect pushing its body forcibly against the walls. The beetles which we have found nestling in this manner have been all males; and therefore it cannot be intended for a breeding-cell; for male insects are never, we believe, sufficiently generous to their mates to assist them in such labours. The beetle in question appears to be partial to celery trenches (J. R.); probably from the loose earth of which they are composed yielding, without much difficulty, to the pressure of its body.

The most destructive, perhaps, of the creatures usually called grubs are the larvæ of the may-bug or cockchafer (Melolontha vulgaris), but too well known, particularly in the southern and midland districts of England, as well as in Ireland, where the grub is called the Connaught worm; but fortunately not abundant in the north. We only once met with the cockchafer in Scotland, at Sorn, in Ayrshire. (J. R.) Even in the perfect state, this insect is not a little destructive to the leaves of both forest and fruit trees. In 1823, we remember to have observed almost all the trees about Dulwich and Camberwell defoliated by them; and Salisbury says, the leaves of the oaks in Richmond Park were so eaten by them, that scarcely an entire leaf was left. But it is in their previous larva state that they are most destructive, as we shall see by tracing their history.

The mother cockchafer, when about to lay her eggs, digs into the earth of a meadow or corn-field to the depth of a span, and deposits them in a cluster at the bottom of the excavation. Rösel, in order to watch the proceedings, put some females into glasses half-filled with earth, covered with a tuft of grass and a piece of thin muslin. In a fortnight, he found some hundreds of eggs deposited, of an oval shape and a pale-yellow colour. Placing the glass in a cellar, the eggs were hatched towards autumn, and the grubs increased remarkably in size. In the following May they fed so voraciously that they required a fresh turf every second day; and even this proving too scanty provender, he sowed in several garden pots a crop of peas, lentils, and salad, and when the plants came up he put a pair of grubs in each pot; and in this manner he fed them through the second and third years. During this period, they cast their skins three or four times, going for this purpose deeper into the earth, and burrowing out a hole where they might effect their change undisturbed; and they do the same in winter, during which they become torpid and do not eat.

When the grub changes into a pupa, in the third autumn after it is hatched, it digs a similar burrow about a yard deep; and when kept in a pot, and prevented from going deep enough, it shows great uneasiness and often dies. The perfect beetle comes forth from the pupa in January or February; but it is then as soft as it was whilst still a grub, and does not acquire its hardness and colour for ten or twelve days, nor does it venture above ground before May, in the fourth year from the time of its hatching. At this time, the beetles may be observed issuing from their holes in the evening, and dashing themselves about in the air as if blind.

During the three summers then of their existence in the grub state, these insects do immense injury, burrowing between the turf and the soil, and devouring the roots of grass and other plants; so that the turf may easily be rolled off, as if cut by a turfing spade, while the soil underneath for an inch or more is turned into soft mould like the bed of a garden. Mr. Anderson, of Norwich, mentions having seen a whole field of fine flourishing grass so undermined by these grubs, that in a few weeks it became as dry, brittle, and withered as hay. Bingley also tells us that "about sixty years ago, a farm near Norwich was so infested with cockchafers, that the farmer and his servants affirmed they gathered eighty bushels of them; and the grubs had done so much injury, that the court of the city, in compassion to the poor fellow's misfortune, allowed him twenty-five pounds." In the year 1785, a farmer, near Blois, in France, employed a number of children and poor persons to destroy the cockchafers at the rate of two liards a hundred, and in a few days they collected fourteen thousand.

"I remember," says Salisbury, "seeing in a nursery near Bagshot, several acres of young forest trees, particularly larch, the roots of which were completely destroyed by it, so much so that not a single tree was left alive." We are doubtful, however, whether this was the grub of the cockchafer, and think it more likely to have been that of the green rose-beetle (Cetonia aurata), which feeds on the roots of trees.

CHAPTER XIV.

ARCHITECTURE OF ANTS.--MASON-ANTS.

All the species of ants are social. There are none solitary, as is the case with bees and wasps. They are all more or less skilful in architecture, some employing masonry, and others being carpenters, wood-carvers, and miners. They consequently afford much that is interesting to naturalists who observe their operations. The genuine history of ants has only been recently investigated, first by Gould in 1747, and subsequently by Linnæus, De Geer, Huber, and Latreille. Previous to that time their real industry and their imagined foresight were held up as moral lessons, without any great accuracy of observation; and it is probable that, even now, the mixture of truth and error in Addison's delightful papers in the Guardian (Nos. 156, 157) may be more generally attractive than the minute relation of careful naturalists. Gould disproved, most satisfactorily, the ancient fable of ants storing up corn for winter provision, no species of ants ever eating grain, or feeding in the winter upon anything. It is to Huber the younger, however, that we are chiefly indebted for our knowledge of the habits and economy of ants; and to Latreille for a closer distinction of the species. Some of the more interesting species, whose singular economy is described by the younger Huber, have not been hitherto found in this country. We shall, however, discover matter of very considerable interest in those which are indigenous; and as our principal object is to excite inquiry and observation with regard to those insects which may be easily watched in our own gardens and fields, we shall chiefly confine ourselves to the ants of these islands. We shall begin with the labours of those native ants which may be called earth-masons, from their digging in the ground, and forming structures with pellets of moistened loam, clay, or sand.

Mason-Ants.

We have used in the preceding pages the terms mason-bees and mason-wasps, for insects which build their nests of earthy materials. On the same principle, we have followed the ingenious M. Huber the younger, in employing the term mason-ants for those whose nests on the exterior appear to be hillocks of earth, without the admixture of other materials, whilst in the interior they present a series of labyrinths, lodges, vaults, and galleries constructed with considerable skill. Of these mason-ants, as of the mason-wasps and bees already described, there are several species, differing from one another in their skill in the art of architecture.

One of the most common of the ant-masons is the turf-ant (Formica cæspitum, Latr.), which is very small and of a blackish-brown colour. Its architecture is not upon quite so extensive a scale as some of the others; but, though slight, it is very ingenious. Sometimes they make choice of the shelter of a flat stone or other covering, beneath which they hollow out chambers and communicating galleries; at other times they are contented with the open ground; but most commonly they select a tuft of grass or other herbage, the stems of which serve for columns to their earthen walls.

We had a small colony of these ants accidentally established in a flower-pot, in which we were rearing some young plants of the tiger-lily (Lilium tigrinum), the stems of which being stronger than the grass where they usually build, enabled them to rear their edifice higher, and also to make it more secure, than they otherwise might. It was wholly formed of small grains of moist earth, piled up between the stems of the lily without any apparent cement; indeed it has been ascertained by Huber, as we shall afterwards see, that they use no cement beside water. This is not always to be procured, as they depend altogether on rains and dew; but they possess the art of joining grains of dry sand so as to support one another, on some similar principle, no doubt, to that of the arch.

The nest which our turf-ants constructed in the flower-pot was externally of an imperfect square form, in consequence of its situation; for they usually prefer a circular plan. The principal chambers were placed under the arches, and, when inspected, contained a pile of cocoons, and pupæ. Beneath those upper chambers there were others dug out deeper down, in which were also a numerous collection of eggs and cocoons in various stages of advancement. (J. R.)

Mr. Knapp describes a still more curious structure of another species of ant common in this country:--"One year," says he, "on the third of March, my labourer being employed in cutting up ant-hills, or tumps as we call them, exposed to view multitudes of the yellow species (Formica flava) in their winter's retirement. They were collected in numbers in little cells and compartments, communicating with others by means of narrow passages. In many of the cells they had deposited their larvæ, which they were surrounding and attending, but not brooding over or covering. Being disturbed by our rude operations, they removed them from our sight to more hidden compartments. The larvæ were small. Some of these ant-hills contained multitudes of the young of the wood-louse (Oniscus armadillo), inhabiting with perfect familiarity the same compartments as the ants, crawling about with great activity with them, and perfectly domesticated with each other. They were small and white; but the constant vibration of their antennæ, and the alacrity of their motions, manifested a healthy vigour. The ants were in a torpid state; but on being removed into a temperate room, they assumed much of their summer's animation. How these creatures are supported during the winter season it is difficult to comprehend; as in no one instance could we perceive any store or provision made for the supply of their wants. The minute size of the larvæ manifested that they had been recently deposited; and consequently that their parents had not remained during winter in a dormant state, and thus free from the calls of hunger. The preceding month of February, and part of January, had been remarkably severe; the frost had penetrated deep into the earth, and long held it frozen; the ants were in many cases not more than four inches beneath the surface, and must have been enclosed in a mass of frozen soil for a long period; yet they, their young, and the onisci, were perfectly uninjured by it: affording another proof of the fallacy of the commonly received opinion, that cold is universally destructive to insect life."

The earth employed by mason-ants is usually moist clay, either dug from the interior parts of their city or moistened by rain. The mining-ants and the ash-coloured (Formica fusca) employ earth which is probably not selected with so much care, for it forms a much coarser mortar than what we see used in the structure of the yellow ants (F. flava) and the brown ants (F. brunnea). We have never observed them bringing their building materials of this kind from a distance, like the mason-bees and like the wood or hill ant (F. rufa); but they take care, before they fix upon a locality, that it shall produce them all that they require. We are indebted to Huber the younger for the most complete account which has hitherto been given of these operations, of which details we shall make free use.

"To form," says this shrewd observer, "a correct judgment of the interior arrangement or distribution of an ant-hill, it is necessary to select such as have not been accidentally spoiled, or whose form has not been too much altered by local circumstances; a slight attention will then suffice to show that the habitations of the different species are not all constructed after the same system. Thus, the hillock raised by the ash-coloured ants will always present thick walls, fabricated with coarse earth, well-marked stories, and large chambers, with vaulted ceilings, resting upon a solid base. We never observe roads, or galleries, properly so called, but large passages, of an oval form, and all around considerable cavities and extensive embankments of earth. We further notice, that the little architects observe a certain proportion between the large arched ceilings and the pillars that are to support them.

"The brown ant (Formica brunnea), one of the smallest of the ants, is particularly remarkable for the extreme finish of its work. Its body is of a reddish shining brown, its head a little deeper, and the antennæ and feet a little lighter in colour. The abdomen is of an obscure brown, the scale narrow, of a square form, and slightly scolloped. The body is one line and two-fifths in length.

"This ant, one of the most industrious of its tribe, forms its nest of stories four or five lines in height. The partitions are not more than half a line in thickness; and the substance of which they are composed is so finely grained, that the inner walls present one smooth unbroken surface. These stories are not horizontal; they follow the slope of the ant-hill, and lie one upon another to the ground-floor, which communicates with the subterranean lodges. They are not always, however, arranged with the same regularity, for these ants do not follow an invariable plan; it appears, on the contrary, that nature has allowed them a certain latitude in this respect, and that they can, according to circumstances, modify them to their wish; but however fantastical their habitations may appear, we always observe they have been formed by concentrical stories. On examining each story separately, we observe a number of cavities or halls, lodges of narrower dimensions, and long galleries, which serve for general communication. The arched ceilings covering the most spacious places are supported either by little columns, slender walls, or by regular buttresses. We also notice chambers, that have but one entrance, communicating with the lower story, and large open spaces, serving as a kind of cross-road (carrefour), in which all the streets terminate.

"Such is the manner in which the habitations of these ants are constructed. Upon opening them, we commonly find the apartments, as well as the large open spaces, filled with adult ants; and always observed their pupæ collected in the apartments more or less near the surface. This, however, seems regulated by the hour of the day, and the temperature: for in this respect these ants are endowed with great sensibility, and know the degree of heat best adapted for their young. The ant-hill contains, sometimes, more than twenty stories in its upper portion, and at least as many under the surface of the ground. By this arrangement the ants are enabled, with the greatest facility, to regulate the heat. When a too-burning sun overheats their upper apartments, they withdraw their little ones to the bottom of the ant-hill. The ground-floor becoming, in its turn, uninhabitable during the rainy season, the ants of this species transport what most interests them to the higher stories; and it is there we find them more usually assembled, with their eggs and pupæ, when the subterranean apartments are submerged."

Ants have a great dislike to water, when it exceeds that of a light shower to moisten their building materials. One species, mentioned by Azara as indigenous to South America, instinctively builds a nest from three to six feet high, to provide against the inundations during the rainy season. Even this, however, does not always save them from submersion; and, when that occurs, they are compelled, in order to prevent themselves from being swept away, to form a group somewhat similar to the curtain of the wax-workers of hive-bees (see p. 133). The ants constituting the basis of this group lay hold of some shrub for security, while their companions hold on by them; and thus the whole colony, forming an animated raft, floats on the surface of the water till the inundation (which seldom continues longer than a day or two) subsides. We confess, however, that we are somewhat sceptical respecting this story, notwithstanding the very high character of the Spanish naturalist.

It is usual with architectural insects to employ some animal secretion, by way of mortar or size, to temper the materials with which they work; but the whole economy of ants is so different, that it would be wrong to infer from analogy a similarity in this respect, though the exquisite polish and extreme delicacy of finish in their structures lead, naturally, to such a conclusion. M. P. Huber, in order to resolve this question, at first thought of subjecting the materials of the walls to chemical analysis, but wisely (as we think) abandoned it for the surer method of observation. The details which he has given, as the result of his researches, are exceedingly curious and instructive. He began by observing an ant-hill till he could perceive some change in its form.

"The inhabitants," says he, "of that which I selected, kept within during the day, or only went out by subterranean galleries which opened at some feet distance in the meadow. There were, however, two or three small openings on the surface of the nest; but I saw none of the labourers pass out this way, on account of their being too much exposed to the sun, which these insects greatly dread. This ant-hill, which had a round form, rose in the grass, at the border of a path, and had sustained no injury. I soon perceived that the freshness of the air and the dew invited the ants to walk over the surface of their nest; they began making new apertures; several ants might be seen arriving at the same time, thrusting their heads from the entrances, moving about their antennæ, and at length adventuring forth to visit the environs.