The Naturalist in Nicaragua Part 7

My house and garden.

Fruits.

Plantains and bananas; probably not indigenous to America: propagated from shoots: do not generally mature their seeds.

Fig-trees.

Granadillas and papaws.

Vegetables.

Dependence of flowers on insects for their fertilisation.

Insect plagues.

Leaf-cutting ants: their method of defoliating trees: their nests.

Some trees are not touched by the ants.

Foreign trees are very subject to their attack.

Method of destroying the ants.

Migration of the ants from a nest attacked.

Corrosive sublimate causes a sort of madness amongst them.

Indian plan of preventing them ascending young trees.

Leaf-cutting ants are fungus-growers and eaters.

Sagacity of the ants.

The gold-mining village of Santo Domingo is situated in the province of Chontales, Nicaragua, in lat.i.tude 12 degrees 16 minutes north and longitude 84 degrees 59 minutes west, nearly midway between the Atlantic and the Pacific, where Central America begins to widen out northward of the narrow isthmus of Panama and Costa Rica. It is in the midst of the great forest that covers most of the Atlantic slope of Central America, and which continues unbroken from where we had entered it, at Pital, eastward to the Atlantic; westward it terminates in a sinuous margin about seven miles from the village, and there commence the lightly timbered and gra.s.sy plains and savannahs stretching to the Lake of Nicaragua.

The surface of the land in the forest region forms a succession of ranges and steep valleys, covered with magnificent timber and much undergrowth. Santo Domingo lies about 2000 feet above the level of the sea, and the hills around it rise from 500 to 1000 feet higher.

It is built in the bend of a small stream, the head waters of a branch of the Blewfields river, on a level, low piece of ground, with the brook winding almost round it, and, beyond that, encircled by an amphitheatre of low hills in the hollow of which it lies. The road to the mines runs through it, and forms the main street, having on each side thatched stores and irregularly built houses.

The inhabitants, about three hundred in number, are entirely dependent on the mines around, there being no cultivation or any other employment in the immediate neighbourhood. The people are of a mixed descent, in which Indian blood predominates, then Spanish with a slight admixture of the Negro element, whilst amongst the rising generation many fair-haired children can claim paternity amongst the numerous German and English workmen that have been employed at the mines. The store-keepers form the aristocracy of the village. They are indolent; lounging about, or lying smoking in their hammocks the greater part of the day, but generally civil and polite. They are particular in their dress, and may often be seen in faultless European costume, silk umbrella in hand, in twos or threes, taking a short quiet walk up the valley. The lower cla.s.s of miners are scantily and badly clothed, especially when they come first to the mines. They are bare-footed, with poor ragged cotton trousers and a thin jacket of the same material. Generally, after being a year or two at the mines, they begin to wear better clothing, and may often be seen with a new shirt, which to show off is worn hanging down outside, like a surtout coat. Amongst these are many pure Indians, short st.u.r.dy men, who make the steadiest workmen, patient and industrious, but with little appreciation of the value of money, and spending the whole of their wages at the end of the month, before they resume work. At these times the commandant comes in from the town of Libertad, about nine miles distant, with half-a-dozen bare-footed soldiers carrying old muskets on their shoulders, and levies blackmail upon the poor patient "Mosas," as they are called, in the shape of a fine for drunkenness. But the "aguardiente," a native-made rum, is nevertheless always kept on hand, being a government monopoly, and ever ready, so that the Mosas may have no excuse to be sober and escape being fined.

Even in their drink the poor Indians are not very violent, and get intoxicated with surprising stolidity and quietness. Amongst the half-breeds, especially where the Negro element exists, there are often quarrellings and rows, when they slash away at each other with their long knives or "machetes," and get ugly cuts, which, however, heal again quickly.

Both the Negroes and Indians are decidedly inferior to the whites in intellect, but they do not differ so much from the Europeans as they do from each other. The Negro will work hard for a short while, on rare occasions, or when compelled by another, but is innately lazy. The Indian is industrious by nature, and works steadily and well for himself; but if compelled to work for another, loses all heart, and pines away and dies. The Negro is talkative, vivacious, vain, and sensual; the Indian taciturn, stolid, dignified, and moderate. As freemen, regularly though poorly paid and kindly treated, the Indians work well and laboriously in the mines; but the Negro seldom engages either in that or any other settled employment, unless compelled as a slave, in which condition he is happy and thoughtless. I do not defend slavery, but I believe it to be a greater curse to the masters than to the slaves, more deteriorating to the former than to the latter.

The Spaniards at first enslaved the Indians, but they died away so rapidly that in a very short time the indigenes of the whole of the once-populous islands of the West Indies were exterminated, and large numbers of Indians were carried off from the mainland to supply their places, but died with equal rapidity; so that the Spaniards found it more profitable to bring negroes from Africa, who thrived and multiplied in captivity as readily as the enslaved Indians pined away and died. In Central America there never were many black slaves; since the States threw off the yoke of Spain there have been none; and this comparative scarcity of the Negro element makes these countries much more pleasant and safer to dwell in than the West Indies, where it is much larger. The Indian seldom or never molests the whites, excepting in retaliation for some great injury; whilst amongst the free Negroes, robbery, violence, and murder need no other incentives than their own evil pa.s.sions and l.u.s.t.

The women at Santo Domingo are much the same as those found at all the small provincial towns of Central America. Morality is at a low ebb, and most of them live as mistresses, not as wives, for which they do not seem to suffer in the estimation of their neighbours.

This is greatly due in Nicaragua, as it is throughout Central and South America, to the profligate lives led by the priests, who, with few rare exceptions, live in concubinage more or less open.

The women have children at an early age, and make kind and indulgent mothers.

(PLATE 4. COMMISSIONER'S HOUSE AT SANTO DOMINGO.)

The village is bounded to the eastward by the mines and hacienda of the Chontales Mining Company, whose houses, workshops, and machinery are on rising ground on each side of the valley, with the brook running down between. About fifty acres of the forest have been cut down, and a great deal of this is fenced in and covered with gra.s.s. Going up the valley from the village, on the right hand side, about fifty yards from the road, on a gra.s.s-covered slope, stand the houses of the commissioner and cashier, in the latter of which the medical officer also lives. The former, a large, white-washed, square, two-storied, wooden house, with verandahs round three sides of it, and communicating by a covered pa.s.sage with a detached kitchen behind, had been built by one of my predecessors, Captain Hill, R.N., who did not live to inhabit it.

It was a roomy, comfortable house, commanding a view of the machinery, workshops, and part of the mines on the other side of the valley, and formed my residence for upwards of four years.

The slope in front of the house, down to the river, was covered with weedy bushes when I arrived; but I had these cleared away, and a fine greensward of gra.s.s took their place. On this I planted young orange, lime, and citron trees; and I had the pleasure, before I left, to see them beginning to bear their fine fruit. To the west of the house was a dell, covered with fallen logs and rubbish thrown from the hill, in which was a perennial spring of limpid water. I had the logs and rubbish gathered together and burnt, put a light fence round it, and formed a small vegetable, fruit, and flower garden. The mango and avocado trees had not come into bearing before I left; but pineapples, figs, grenadillas, bananas, pumpkins, plantains, papaws, and chioties fruited abundantly. The last named is a native of Mexico; it is a climbing plant with succulent stems and vine-like leaves, and grows with great rapidity. The fruit, of which it bears a great abundance, is about the size and shape of a pear, covered with soft p.r.i.c.kles. It is boiled and eaten as a vegetable, and resembles vegetable marrow.

At Santo Domingo it continues to bear a succession of fruits during eight months of the year.

Next to maize, plantains and bananas form the princ.i.p.al sustenance of the natives. The banana tree shoots up its succulent stem, and unfolds its immense entire leaves with great rapidity; and a group of them waving their silky leaves in the sun, or shining ghostly white in the moonlight, forms one of those beautiful sights that can only be seen to perfection in the tropics. There are a great many varieties of them, and they are cooked in many ways--boiled, baked, made into pastry, or eaten as a fruit. The varieties differ not only in their fruits, but in the colour of their leaves and stems; the natives can distinguish them without seeing the fruit, and have names for each, by which they are known throughout all Central America, Mexico, and Peru. These names are of Spanish origin; and this fact, together with the absence of any native, Mexican, or Peruvian name for the fruit, inclines me to adopt the opinion of Clavigero, who contends, in opposition to other writers, that the plantain and banana were not known in these countries before the Spanish conquest, but were first brought from the Canaries to Hayti in 1516, and from thence taken to the mainland.

Neither the sugar-cane* nor the plantain is given in the list of the indigenous productions of Mexico by the careful and accurate Hernandez. (* The sugar-cane is said never to bear seed in the West Indies, Malaga, India, Cochin China, or the Malay Archipelago.

--Darwin's "Animals and Plants under Domestication" volume 2 page 169.) The natives made sugar from the green stems of the maize.

Humboldt thinks that some species of plantain were indigenous to America; but it seems incredible that such an important fruit could have been overlooked by the early historians. In the old world the cultivation of the banana dates from the earliest times of which tradition makes mention. One of the Sanscrit names was bhanu--fruit, from which probably the name "banana" was derived.*

(* Humboldt's "Aspects of Nature" volume 2 page 141.)

Both the plantain and the banana are always propagated from shoots or suckers that spring from the base of the plants; and it is to be remarked that the pineapple and the bread-fruit, that are also universally grown from cuttings or shoots, and have been cultivated from remote antiquity, have in a great measure lost the faculty of producing mature seed. Such varieties could not arise in a state of nature, but are due to selection by early races of mankind, who would naturally propagate the best varieties; and, to do this, seed was not required. As the finest kinds of bananas, pineapples, and bread-fruit are almost seedless, it is probable that the nutriment that would have been required for the formation of the seeds has been expended in producing larger and more succulent fruits. We find some varieties of oranges, which also have been cultivated from very early ages, producing fruits without seeds; but as these trees are propagated from seeds, these varieties could not become so sterile as those just mentioned. There can be no doubt that the seedless varieties of banana, bread-fruits, and pineapples have been propagated for hundreds of years; and this fact ought to modify the opinions generally entertained by horticulturists that the life of plants and trees propagated from shoots or cuttings cannot be indefinitely prolonged in that way. Perhaps this may be the case in trees, such as apples, that have come under their notice; and the reason that the varieties die out after a certain time, if not reproduced from seed, may be that the vigour of the trees is at last used up by the production of mature seed, but that in the seedless bananas, pineapples, and bread-fruits this does not happen.

Figs grow well in Nicaragua, and by many their luscious fruit is preferred to all others. My trees suffered greatly from the attacks of a large and fine longicorn beetle (Taeniotes scalaris, Fab.) which laid its eggs in the green bark, and produced white grubs that mined into the stem. I had to dig down to them with a knife to extricate them and prevent them destroying the young trees. We were surrounded at a short distance by the forest, in which grow many species of wild fig-trees; and this probably was the reason that my trees suffered so much, for at Granada the fig-growers were not troubled with this insect.

The grenadilla is the fruit of one of the pa.s.sion-flowers (Pa.s.siflora quadrangularis), and is shaped like a large oblong apple, which it also resembles in perfume. It makes fine tarts and puddings, being somewhat like the gooseberry in taste. I had much difficulty in preserving it from being eaten by small forest rats that came out of the woods, where they had already been accustomed to eat the wild fruit of this climber.

The moist, warm climate seemed to suit the papaw tree, as it grew with great vigour, and produced very large and fine melon-like fruits. The green fruits are excellent for making pastry, if flavoured with a little lime-juice.

In vegetables, I grew three species of sweet potatoes--yellow, purple, and white skinned, and which differ also in their leaves and flowers; cabbages, kidney-beans, pumpkins, yuccas (Jatropha manihot), quequisque (a species of arum, Colocasia esculenta), lettuces, tomatoes, capisc.u.ms, endives, parsley, and carrots.

The climate was too damp to grow onions; neither could I succeed with peas, potatoes, or turnips. Scarlet runners (Phaseolus multiflorus) grew well, and flowered abundantly, but never produced a single pod. Darwin has shown that this flower is dependent, like many others, for its fertilisation upon the operations of the busy humble-bee, and that it is provided with a wonderful mechanism, by means of which its pollen is rubbed into the head of the bee, and received on the stigma of the next plant visited.* (* "Gardener's Chronicle" October 24, 1857 and November 14, 1858; also T.H. Farrer in "Annals of Natural History" October 1868.) There are many humble-bees, of different species from ours, in tropical America; but none of them frequented the flowers of the scarlet runner, and to that circ.u.mstance we may safely ascribe its sterility. An a.n.a.logous case has been long known. The vanilla plant (Vanilla planifolia) has been introduced from tropical America into India, but though it grows well, and flowers, it never fruits without artificial aid. It is the same in the hothouses of Europe. Dr.

Morren, of Liege, has shown that, if artificially fertilised, every flower will produce fruit; and ascribes its sterility to the absence, in Europe and India, of some insect that in America carries the pollen from one flower to another.* (* Taylor's "Annals of Natural History" volume 3 page 1.) When those interested in the acclimature of the natural productions of one country on the soil of some distant one, study the mutual relations of plants and animals, they will find that in the case of many plants it is important that the insects specially adapted for the fertilisation of their flowers should be introduced with them. Thus, if the insect or bird that a.s.sists in the fertilisation of the vanilla could be introduced into and would live in India, the growers of that plant would be relieved of much trouble, and it might be thoroughly naturalised. Judging from my experience, it would be useless to attempt the acclimature of the scarlet-runner bean in Chontales unless the humble-bee were also introduced.

Caterpillars, plant-lice, bugs, and insect pests of all kinds were numerous, and did much harm to my garden; but the greatest plague of all were the leaf-cutting ants, and I had to wage a continual warfare against them. During this contest I gained much information regarding their habits, and was successful in checking their ravages, and I shall occupy the remainder of this chapter with an account of them.

LEAF-CUTTING ANTS.

Nearly all travellers in tropical America have described the ravages of the leaf-cutting ants (Oecodoma); their crowded, well-worn paths through the forests, their ceaseless pertinacity in the spoliation of the trees--more particularly of introduced species--which are stripped bare and ragged with the midribs and a few jagged points of the leaves only left. Many a young plantation of orange, mango, and lemon trees has been destroyed by them. Again and again have I been told in Nicaragua, when inquiring why no fruit-trees were grown at particular places, "It is no use planting them; the ants eat them up." The first acquaintance a stranger generally makes with them is on encountering their paths on the outskirts of the forest crowded with the ants; one lot carrying off the pieces of leaves, each piece about the size of a sixpence, and held up vertically between the jaws of the ant; another lot hurrying along in an opposite direction empty-handed, but eager to get loaded with their leafy burdens. If he follows this last division, it will lead him to some young trees or shrubs, up which the ants mount; and then each one, stationing itself on the edge of a leaf, commences to make a circular cut, with its scissor-like jaws, from the edge, its hinder feet being the centre on which it turns. When the piece is nearly cut off, it is still stationed upon it, and it looks as though it would fall to the ground with it; but, on being finally detached, the ant is generally found to have hold of the leaf with one foot, and soon righting itself, and arranging its burden to its satisfaction, it sets off at once on its return. Following it again, it is seen to join a throng of others, each laden like itself, and, without a moment's delay, it hurries along the well-worn path. As it proceeds, other paths, each thronged with busy workers, come in from the sides, until the main road often gets to be seven or eight inches broad, and more thronged than the streets of the city of London.

After travelling for some hundreds of yards, often for more than half a mile, the formicarium is reached. It consists of low, wide mounds of brown, clayey-looking earth, above and immediately around which the bushes have been killed by their buds and leaves having been persistently bitten off as they attempted to grow after their first defoliation. Under high trees in the thick forest the ants do not make their nests, because, I believe, the ventilation of their underground galleries, about which they are very particular, would be interfered with, and perhaps to avoid the drip from the trees.

It is on the outskirts of the forest, or around clearings, or near wide roads that let in the sun, that these formicariums are generally found. Numerous round tunnels, varying from half an inch to seven or eight inches in diameter, lead down through the mounds of earth; and many more from some distance around, also lead underneath them. At some of the holes on the mounds ants will be seen busily at work, bringing up little pellets of earth from below, and casting them down on the ever-increasing mound, so that its surface is nearly always fresh and new-looking.

Standing near the mounds, one sees from every point of the compa.s.s ant-paths leading to them, all thronged with the busy workers carrying their leafy burdens. As far as the eye can distinguish their tiny forms, troops upon troops of leaves are moving up towards the central point, and disappearing down the numerous tunnelled pa.s.sages. The out-going, empty-handed hosts are partly concealed amongst the bulky burdens of the incomers, and can only be distinguished by looking closely amongst them. The ceaseless, toiling hosts impress one with their power, and one asks--What forests can stand before such invaders? How is it that vegetation is not eaten off the face of the earth? Surely nowhere but in the tropics, where the recuperative powers of nature are immense and ever active, could such devastation be withstood.

Further acquaintance with the subject will teach the inquirer that, just as many insects are preserved by being distasteful to insectivorous birds, so very many of the forest trees are protected from the ravages of the ants by their leaves either being distasteful to them, or unfitted for the purpose for which they are required, whilst some have special means of defence against their attacks. None of the indigenous trees appear so suitable for them as the introduced ones. Through long ages the trees and the ants of tropical America have been modified together. Varieties of plants that arose unsuitable for the ants have had an immense advantage over others that were more suitable; and thus through time every indigenous tree that has survived in the great struggle has done so because it has had originally, or has acquired, some protection against the great destroyer. The leaf-cutting ants are confined to tropical America; and we can easily understand that trees and vegetables introduced from foreign lands where these ants are unknown could not have acquired, excepting accidentally, and without any reference to the ants, any protection against their attacks, and now they are most eagerly sought by them. Amongst introduced trees, some species of even the same genus are more acceptable than others. Thus, in the orange tribe, the lime (Citrus lemonum) is less liked than the other species; it is the only one that I ever found growing really wild in Central America: and I have sometimes thought that even in the short time since the lime was first introduced, about three hundred years ago, a wild variety may have arisen, less subject to the attacks of the ants than the cultivated variety; for in many parts I saw them growing wild, and apparently not touched. The orange (Citrus aurantium) and the citron (Citrus medicus), on the other hand, are only found where they have been planted and protected by man; and, were he to give up their cultivation, the only species that would ultimately withstand the attacks of the ants, and obtain a permanent footing in Central America, would be the lime. The reason why the lime is not so subject to the attacks of the ants is unknown; and the fact that it is so is another instance of how little we know why one species of a particular genus should prevail over another nearly similar form. A little more or less acridity, or a slight chemical difference in the composition of the tissues of a leaf, so small that it is inappreciable to our senses, may be sufficient to ensure the preservation or the destruction of a species throughout an entire continent.

The ravages of this ant are so great that it may not be without interest for me to enter upon some details respecting the means I took to protect my own garden against their attacks, especially as the continual warfare I waged against them for more than four years made me acquainted with much of their wonderful economy.

In June 1869, very soon after the formation of my garden, the leaf-cutting ants came down upon it, and at once commenced denuding the young bananas, orange, and mango trees of their leaves. I followed up the paths of the invading hosts to their nest, which was about one hundred yards distant, close to the edge of the forest. The nest was not a very large one, the low mound of earth covering it being about four yards in diameter. At first I tried to stop the holes up, but fresh ones were immediately opened out: I then dug down below the mound, and laid bare the chambers beneath, filled with ant-food and young ants in every stage of growth; but I soon found that the underground ramifications extended so far, and to so great a depth, while the ants were continually at work making fresh excavations, that it would be an immense task to eradicate them by such means; and notwithstanding all the digging I had done the first day, I found them the next as busily at work as ever at my garden, which they were rapidly defoliating. At this stage, our medical officer, Dr. J.H. Simpson,* came to my a.s.sistance, and suggested pouring carbolic acid, mixed with water, down their burrows. (* This gentleman, beloved by all who knew him, of rare talent, and with every prospect of a prosperous career before him, died at Jamaica from hydrophobia, between two and three months after being bitten by a small dog that had not itself shown any symptoms of that disease.) The suggestion proved a most valuable one. We had a quant.i.ty of common brown carbolic acid, about a pint of which I mixed with four buckets of water, and, after stirring it well about, poured it down the burrows; I could hear it rumbling down to the lowest depths of the formicarium four or five feet from the surface. The effect was all I could have wished: the marauding parties were at once drawn off from my garden to meet the new danger at home. The whole formicarium was disorganised. Big fellows came stalking up from the cavernous regions below, only to descend again in the utmost perplexity.

Next day I found them busily employed bringing up the ant-food from the old burrows, and carrying it to a new one a few yards distant; and here I first noticed a wonderful instance of their reasoning powers. Between the old burrows and the new one was a steep slope.

Instead of descending this with their burdens, they cast them down on the top of the slope, whence they rolled down to the bottom, where another relay of labourers picked them up and carried them to the new burrow. It was amusing to watch the ants hurrying out with bundles of food, dropping them over the slope, and rushing back immediately for more. They also brought out great numbers of dead ants that the fumes of the carbolic acid had killed. A few days afterwards, when I visited the locality again, I found both the old burrows and the new one entirely deserted, and I thought they had died off; but subsequent events convinced me that the survivors had only moved away to a greater distance.

It was fully twelve months before my garden was again invaded. I had then a number of rose-trees and also cabbages growing, which the ants seemed to prefer to everything else. The rose-trees were soon defoliated, and great havoc was made amongst the cabbages. I followed them to their nest, and found it about two hundred yards from the one of the year before. I poured down the burrows, as before, several buckets of water with carbolic acid. The water is required to carry the acid down to the lowest chambers. The ants, as before, were at once withdrawn from my garden; and two days afterwards, on visiting the place, I found all the survivors at work on one track that led directly to the old nest of the year before, where they were busily employed making fresh excavations.

Many were bringing along pieces of the ant-food from the old to the new nests; others carried the undeveloped white pupae and larvae.

It was a wholesale and entire migration; and the next day the formicarium down which I had last poured the carbolic acid was entirely deserted. I afterwards found that when much disturbed, and many of the ants destroyed, the survivors migrate to a new locality. I do not doubt that some of the leading minds in this formicarium recollected the nest of the year before, and directed the migration to it.

Don Francisco Velasquez informed me, in 1870, that he had a powder which made the ants mad, so that they bit and destroyed each other.

He gave me a little of it, and it proved to be corrosive sublimate.

I made several trials of it, and found it most efficacious in turning a large column of the ants. A little of it sprinkled across one of their paths in dry weather has a most surprising effect. As soon as one of the ants touches the white powder, it commences to run about wildly, and attack any other ant it comes across. In a couple of hours, round b.a.l.l.s of the ants will be found all biting each other; and numerous individuals will be seen bitten completely in two, whilst others have lost some of their legs or antennae.

News of the commotion is carried to the formicarium, and huge fellows, measuring three-quarters of an inch in length, that only come out of the nest during a migration or an attack on the nest or one of the working columns, are seen stalking down with a determined air, as if they would soon right matters. As soon, however, as they have touched the sublimate, all their stateliness leaves them: they rush about; their legs are seized hold of by some of the smaller ants already affected by the poison; and they themselves begin to bite, and in a short time become the centres of fresh b.a.l.l.s of rabid ants. The sublimate can only be used effectively in dry weather. At Colon I found the Americans using coal tar, which they spread across their paths when any of them led to their gardens. I was also told that the Indians prevent them from ascending young trees by tying thick wisps of gra.s.s, with the sharp points downwards, round the stems. The ants cannot pa.s.s through the wisp, and do not find out how to surmount it, getting confused amongst the numberless blades, all leading downwards. I mention these different plans of meeting and frustrating the attacks of the ants at some length, as they are one of the greatest scourges of tropical America, and it has been too readily supposed that their attacks cannot be warded off. I myself was enabled, by using some of the means mentioned above, to cultivate successfully trees and vegetables of which the ants were extremely fond.

(PLATE 5. NEST OF LEAF-CUTTING ANT.)

Notwithstanding that these ants are so common throughout tropical America, and have excited the attention of nearly every traveller, there still remains much doubt as to the use to which the leaves are put. Some naturalists have supposed that they use them directly as food; others, that they roof their underground nests with them.

I believe the real use they make of them is as a manure, on which grows a minute species of fungus, on which they feed;--that they are, in reality, mushroom growers and eaters. This explanation is so extraordinary and unexpected, that I may be permitted to enter somewhat at length on the facts that led me to adopt it. When I first began my warfare against the ants that attacked my garden, I dug down deeply into some of their nests. In our mining operations we also, on two occasions, carried our excavations from below up through very large formicariums, so that all their underground workings were exposed to observation. I found their nests below to consist of numerous rounded chambers, about as large as a man's head, connected together by tunnelled pa.s.sages leading from one chamber to another. Notwithstanding that many columns of the ants were continually carrying in the cut leaves, I could never find any quant.i.ty of these in the burrows, and it was evident that they were used up in some way immediately they were brought in. The chambers were always about three parts filled with a speckled, brown, flocculent, spongy-looking ma.s.s of a light and loosely connected substance. Throughout these ma.s.ses were numerous ants belonging to the smallest division of the workers, which do not engage in leaf-carrying. Along with them were pupae and larvae, not gathered together, but dispersed, apparently irregularly, throughout the flocculent ma.s.s. This ma.s.s, which I have called the ant-food, proved, on examination, to be composed of minutely subdivided pieces of leaves, withered to a brown colour, and overgrown and lightly connected together by a minute white fungus that ramified in every direction throughout it. I not only found this fungus in every chamber I opened, but also in the chambers of the nest of a distinct species that generally comes out only in the night-time, often entering houses and carrying off various farinaceous substances, and which does not make mounds above its nests, but long, winding pa.s.sages, terminating in chambers similar to the common species, and always, like them, three parts filled with flocculent ma.s.ses of fungus-covered vegetable matter, amongst which are the ant-nurses and immature ants. When a nest is disturbed, and the ma.s.ses of ant-food spread about, the ants are in great concern to carry every morsel of it under shelter again; and sometimes, when I had dug into a nest, I found the next day all the earth thrown out filled with little pits that the ants had dug into it to get out the covered up food. When they migrate from one part to another, they also carry with them all the ant-food from their old habitations. That they do not eat the leaves themselves I convinced myself; for I found near the tenanted chambers, deserted ones filled with the refuse particles of leaves that had been exhausted as manure for the fungus, and were now left, and served as food for larvae of Staphylinidae and other beetles.* (*This theory that the leaf-cutting ants feed on a fungus which they cultivate has been confirmed by Mr. Fritz Muller, who had arrived at it independently in Brazil. His observations on this and various other habits of insects are contained in a letter to Mr. Charles Darwin, published in "Nature" of June 11, 1874.)

These ants do not confine themselves to leaves, but also carry off any vegetable substance that they find suitable for growing the fungus on. They are very partial to the inside white rind of oranges, and I have also seen them cutting up and carrying off the flowers of certain shrubs, the leaves of which they neglected. They are particular about the ventilation of their underground chambers, and have numerous holes leading up to the surface from them. These they open out or close up, apparently to keep up a regular degree of temperature below. The great care they take that the pieces of leaves they carry into the nest should be neither too dry nor too damp, is also consistent with the idea that the object is the growth of a fungus that requires particular conditions of temperature and moisture to ensure its vigorous growth. If a sudden shower should come on, the ants do not carry the wet pieces into the burrows, but throw them down near the entrances. Should the weather clear up again, these pieces are picked up when nearly dried, and taken inside; should the rain, however, continue, they get sodden down into the ground, and are left there. On the contrary, in dry and hot weather, when the leaves would get dried up before they could be conveyed to the nest, the ants, when in exposed situations, do not go out at all during the hot hours, but bring in their leafy burdens in the cool of the day and during the night. As soon as the pieces of leaves are carried in they must be cut up by the small cla.s.s of workers into little pieces. I have never seen the smallest cla.s.s of ants carrying in leaves; their duties appear to be inside, cutting them up into smaller fragments, and nursing the immature ants. I have, however, seen them running out along the paths with the others; but instead of helping to carry in the burdens, they climb on the top of the pieces which are being carried along by the middle-sized workers, and so get a ride home again. It is very probable that they take a run out merely for air and exercise. The largest cla.s.s of what are called workers are, I believe, the directors and protectors of the others. They are never seen out of the nest, excepting on particular occasions, such as the migrations of the ants, and when one of the working columns or nests is attacked; they then come stalking up, and attack the enemy with their strong jaws. Sometimes, when digging into the burrows, one of these giants has unperceived climbed up my dress, and the first intimation of his presence has been the burying of his jaws in my neck, from which he would not fail to draw the blood. The stately observant way in which they stalk about, and their great size, compared with the others, always impressed me with the idea that in their bulky heads lay the brains that directed the community in its various duties. Many of their actions, such as that I have mentioned of two relays of workmen carrying out the ant-food, can scarcely be blind instinct. Some of the ants make mistakes, and carry in unsuitable leaves. Thus gra.s.s is nearly always rejected by them, yet I have seen some ants, perhaps young ones, carrying in leaves of gra.s.s. After a while these pieces were invariably brought out again and thrown away. I can imagine a young ant getting a severe earwigging from one of the major-domos for its stupidity.

I shall conclude this long account of the leaf-cutting ants with an instance of their reasoning powers. A nest was made near one of our tramways, and to get to the trees the ants had to cross the rails, over which the waggons were continually pa.s.sing and repa.s.sing.

Every time they came along a number of ants were crushed to death.

They persevered in crossing for several days, but at last set to work and tunnelled underneath each rail. One day, when the waggons were not running, I stopped up the tunnels with stones; but although great numbers carrying leaves were thus cut off from the nest, they would not cross the rails, but set to work making fresh tunnels underneath them. Apparently an order had gone forth, or a general understanding been come to, that the rails were not to be crossed.