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.”CO
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.CP
“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.”CQ
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,CR 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.
“This brought to my recollection a singular opinion of the ancients. They believed that ants were occupied in their architectural labours during the night, when the moon was at its full.”CS
M. Latreille discovered a species of ants which were, so far as he could ascertain, completely blind,CT and of course it would be immaterial to them whether they worked by night or during the day. All observers indeed agree that ants labour in the night, and a French naturalist is therefore of opinion that they never sleep—a circumstance which is well ascertained with respect to other animals, such as the shark, which will track a ship in full sail for weeks together.CU The ingenious historian of English ants, Gould, says they never intermit their labours by night or by day, except when compelled by excessive rains. It is probable the ancients were mistaken in asserting that they only work when the moon shines;CV for, like bees, they seem to find no difficulty in building in the dark, their subterranean apartments being as well finished as the upper stories of their buildings. But to proceed with the narrative of M. P. Huber.
“Having thus noticed the movements of these insects during the night, I found they were almost always abroad and engaged about the dome of their habitation after sunset. This was directly the reverse of what I had observed in the conduct of the wood-ants (F. rufa), who only go out during the day, and close their doors in the evening. The contrast was still more remarkable than I had previously supposed; for, upon visiting the brown ants some days after, during a gentle rain, I saw all their architectural talents in full play.
“As soon as the rain commenced, they left in great numbers their subterranean residence, re-entered it almost immediately, and then returned, bearing between their teeth pellets of earth, which they deposited on the roof of their nest. I could not at first conceive what this was meant for, but at length I saw little walls start up on all sides with spaces left between them. In several places, columns, ranged at regular distances, announced halls, lodges, and passages which the ants proposed establishing; in a word, it was the rough beginning of a new story.
“I watched with a considerable degree of interest the most trifling movements of my masons, and found they did not work after the manner of wasps and humble-bees, when occupied in constructing a covering to their nest. The latter sit, as it were, astride on the border or margin of the covering, and take it between their teeth to model and attenuate it according to their wish. The wax of which it is composed, and the paper which the wasp employs, moistened by some kind of glue, are admirably adapted for this purpose, but the earth of which the ants make use, from its often possessing little tenacity, must be worked up after some other manner.
“Each ant, then, carried between its teeth the pellet of earth it had formed by scraping with the end of its mandibles the bottom of its abode, a circumstance which I have frequently witnessed in open day. This little mass of earth, being composed of particles but just united, could be readily kneaded and moulded as the ants wished; thus when they had applied it to the spot where they had to rest, they divided and pressed against it with their teeth, so as to fill up the little inequalities of their wall. The antennæ followed all their movements, passing over each particle of earth as soon as it was placed in its proper position. The whole was then rendered more compact by pressing it lightly with the fore-feet. This work went on remarkably fast. After having traced out the plan of their masonry, in laying here and there foundations for the pillars and partitions they were about to erect, they raised them gradually higher, by adding fresh materials. It often happened that two little walls, which were to form a gallery, were raised opposite, and at a slight distance from each other. When they had attained the height of four or five lines, the ants busied themselves in covering in the space left between them by a vaulted ceiling.
“As if they judged all their partitions of sufficient elevation, they then quitted their labours in the upper part of the building; they affixed to the interior and upper part of each wall fragments of moistened earth, in an almost horizontal direction, and in such a way as to form a ledge, which, by extension, would be made to join that coming from the opposite wall. These ledges were about half a line in thickness; and the breadth of the galleries was, for the most part, about a quarter of an inch. On one side several vertical partitions were seen to form the scaffolding of a lodge, which communicated with several corridors by apertures formed in the masonry; on another, a regularly-formed hall was constructed, the vaulted ceiling of which was sustained by numerous pillars; further off, again, might be recognised the rudiments of one of those cross roads of which I have before spoken, and in which several avenues terminate. These parts of the ant-hill were the most spacious; the ants, however, did not appear embarrassed in constructing the ceiling to cover them in, although they were often more than two inches in breadth.
“In the upper part of the angles formed by the different walls, they laid the first foundations of this ceiling, and from the top of each pillar, as from so many centres, a layer of earth, horizontal and slightly convex, was carried forward to meet the several portions coming from different points of the large public thoroughfare.
“I sometimes, however, laboured under an apprehension that the building could not possibly resist its own weight, and that such extensive ceilings, sustained only by a few pillars, would fall into ruin from the rain which continually dropped upon them; but I was quickly convinced of their stability, from observing that the earth brought by these insects adhered at all points, on the slightest contact; and that the rain, so far from lessening the cohesion of its particles, appeared even to increase it. Thus, instead of injuring the building, it even contributed to render it still more secure.
“These particles of moistened earth, which are only held together by juxtaposition, require a fall of rain to cement them more closely, and thus varnish over, as it were, those places where the walls and galleries remain uncovered. All inequalities in the masonry then disappear. The upper part of these stories, formed of several pieces brought together, presents but one single layer of compact earth. They require for their complete consolidation nothing but the heat of the sun. It sometimes, however, happens that a violent rain will destroy the apartments, especially should they be but slightly arched; but under these circumstances the ants reconstruct them with wonderful patience.
“These different labours were carried on at the same time, and were so closely followed up in the different quarters, that the ant-hill received an additional story in the course of seven or eight hours. All the vaulted ceilings being formed upon a regular plan, and at equal distances from one wall to the other, constituted, when finished, but one single roof. Scarcely had the ants finished one story than they began to construct another; but they had not time to finish it—the rain ceasing before the ceiling was fully completed. They still, however, continued their work for a few hours, taking advantage of the humidity of the earth; but a keen north wind soon sprung up, and hastily dried the collected fragments, which, no longer possessing the same adherence, readily fell into powder. The ants, finding their efforts ineffectual, were at length discouraged, and abandoned their employment; but what was my astonishment when I saw them destroy all the apartments that were yet uncovered, scattering here and there over the last story the materials of which they had been composed! These facts incontestably prove that they employ neither gum, nor any kind of cement, to bind together the several substances of their nest; but in place of this avail themselves of the rain, to work or knead the earth, leaving the sun and wind to dry and consolidate it.”CW
Dr. Johnson of Bristol observed very similar proceedings in the case of a colony of red ants (Myrmica rubra?), the roof of whose nest was formed by a flat stone. During dry weather, a portion of the side walls fell in; but the rubbish was quickly removed, though no repairs were attempted till a shower of rain enabled them to work. As soon as this occurred, they worked with extraordinary rapidity, and in a short time the whole of the fallen parts were rebuilt, and rendered as smooth as if polished with a trowel.
When a gardener wishes to water a plot of ground where he has sown seeds that require nice management, he dips a strong brush into water, and passes his hand backwards and forwards over the hairs for the purpose of producing a fine artificial shower. Huber successfully adopted the same method to excite his ants to recommence their labours, which had been interrupted for want of moisture. But sometimes, when they deem it unadvisable to wait for rain, they dig down (as we remarked to be the practice of the mason-bees) till they arrive at earth sufficiently moist for their purpose. They do not, however, like these bees, merely dig for materials; for they use the excavations for apartments, as well as what they construct with the materials thence derived. They appear, in short, to be no less skilful in mining than in building.
Such is the general outline of the operations of this singular species; but we are still more interested with the history which M. P. Huber has given of the labours of an individual ant. “One rainy day,” he says, “I observed a labourer of the dark ash-coloured species (Formica fusca) digging the ground near the aperture which gave entrance to the ant-hill. It placed in a heap the several fragments it had scraped up, and formed them into small pellets, which it deposited here and there upon the nest. It returned constantly to the same place, and appeared to have a particular design, for it laboured with ardour and perseverance. I remarked a slight furrow, excavated in the ground in a straight line, representing the plan of a path or gallery. The labourer (the whole of whose movements fell under my immediate observation) gave it greater depth and breadth, and cleared out its borders; and I saw, at length—in which I could not be deceived—that it had the intention of establishing an avenue which was to lead from one of the stories to the underground chambers. This path, which was about two or three inches in length, and formed by a single ant, was opened above, and bordered on each side by a buttress of earth. Its concavity, in the form of a pipe (gouttière), was of the most perfect regularity: for the architect had not left an atom too much. The work of this ant was so well followed and understood, that I could almost to a certainty guess its next proceeding, and the very fragment it was about to remove. At the side of the opening where this path terminated was a second opening, to which it was necessary to arrive by some road. The same ant began and finished this undertaking without assistance. It furrowed out and opened another path, parallel to the first, leaving between each a little wall of three or four lines in height.”
Like the hive-bees, ants do not seem to work in concert, but each individual separately. There is, consequently, an occasional want of coincidence in the walls and arches; but this does not much embarrass them, for a worker, on discovering an error of this kind, seems to know how to rectify it, as appears from the following observations:—
“A wall,” says M. Huber, “had been erected, with the view of sustaining a vaulted ceiling, still incomplete, that had been projected towards the wall of the opposite chamber. The workman who began constructing it had given it too little elevation to meet the opposite partition, upon which it was to rest. Had it been continued on the original plan, it must infallibly have met the wall at about one-half of its height; and this it was necessary to avoid. This state of things very forcibly claimed my attention; when one of the ants arriving at the place, and visiting the works, appeared to be struck by the difficulty which presented itself; but this it as soon obviated, by taking down the ceiling, and raising the wall upon which it reposed. It then, in my presence, constructed a new ceiling with the fragments of the former one.
“When the ants commence any undertaking, one would suppose that they worked after some preconceived idea, which, indeed, would seem verified by the execution. Thus, should any ant discover upon the nest two stalks of plants which lie crossways, a disposition favourable to the construction of a lodge, or some little beams that may be useful in forming its angles and sides, it examines the several parts with attention; then distributes, with much sagacity and address, parcels of earth in the spaces, and along the stems, taking from every quarter materials adapted to its object, sometimes not caring to destroy the work that others had commenced; so much are its motions regulated by the idea it has conceived, and upon which it acts, with little attention to all else around it. It goes and returns, until the plan is sufficiently understood by its companions.
“In another part of the same ant-hill,” continues M. Huber, “several fragments of straw seemed expressly placed to form the roof of a large house: a workman took advantage of this disposition. These fragments lying horizontally, at half-an-inch distance from the ground, formed, in crossing each other, an oblong parallelogram. The industrious insect commenced by placing earth in the several angles of this framework, and all along the little beams of which it was composed. The same workman afterwards placed several rows of the same materials against each other, when the roof became very distinct. On perceiving the possibility of profiting by another plant to support a vertical wall, it began laying the foundations of it; other ants having by this time arrived, finished in common what this had commenced.”CX
M. Huber made most of his observations upon the processes followed by ants in glazed artificial hives or formicaries. The preceding figure represents a view of one of his formicaries of mason-ants.
We have ourselves followed up his observations, both on natural ant-hills and in artificial formicaries. On digging cautiously into a natural ant-hill, established upon the edge of a garden-walk, we were enabled to obtain a pretty complete view of the interior structure. There were two stories, composed of large chambers, irregularly oval, communicating with each other by arched galleries, the walls of all which were as smooth and well-polished as if they had been passed over by a plasterer’s trowel. The floors of the chambers, we remarked, were by no means either horizontal or level, but all more or less sloped, and exhibiting in each chamber at least two slight depressions of an irregular shape. We left the under story of this nest untouched, with the notion that the ants might repair the upper galleries, of which we had made a vertical section; but instead of doing so they migrated during the day to a large crack formed by the dryness of the weather, about a yard from their old nest. (J. R.)
We put a number of yellow ants (Formica flava), with their eggs and cocoons, into a small glass frame, more than half full of moist sand taken from their native hill, and placed in a sloping position, in order to see whether they would bring the nearly vertical, and therefore insecure, portion to a level by masonry. We were delighted to perceive that they immediately resolved upon performing the task which had been assigned them, though they did not proceed very methodically in their manner of building; for instead of beginning at the bottom and building upwards, many of them went on to add to the top of the outer surface, which increased rather than diminished the insecurity of the whole. Withal, however, they seemed to know how far to go, for no portion of the newly-built wall fell; and in two days they had not only reared a pyramidal mound to prop the rest, but had constructed several galleries and chambers for lodging the cocoons, which we had scattered at random amongst the sand. The new portion of this building is represented in the figure as supporting the upper and insecure parts of the nest.
We are sorry to record that our ingenious little masons were found upon the third day strewed about the outside of the building dead or dying, either from over-fatigue or perhaps from surfeit, as we had supplied them with as much honey as they could devour. A small colony of turf-ants have at this moment (July 28th, 1829) taken possession of the premises of their own accord. (J. R.)