Chapter IV: Part I: Harvesting Ants (2)

One of these tunnels at first took a horizontal course for two and a half inches, then descended vertically for an inch and a half to a point where it made two horizontal branches, and from these latter several other vertical galleries descended, two of which we were able to trace until they expanded into a cluster of small pear-shaped cells, the walls of which were quite smooth and very carefully laid with plates of mica and cement. I was able to draw this on the spot, Fig. A, Plate V., while Mr. Lightbody worked it out piecemeal with hammer and chisel. It was unfortunately impossible to secure more than very imperfect fragments as specimens. These terminal cells were empty when we came to them, but it is quite possible that the ants may have conveyed away larvæ or winged ants from them, having received abundant notice of the coming danger from the continued jarring of the chisel-work.

One entrance to this nest lay in a small accumulation of soil in a hollow of the rock, and it was at this point that the refuse from the nest was cast out. Indeed, had it not been for the accidental circumstance of my having traced the ants to the newly hewn step in the sandstone, I might never have discovered the fact that the nests are sometimes carried deep into the living rock.

With this to guide me, however, I succeeded in finding a second nest of the same kind, and here I was able to secure better specimens of the tunnels for drawing (Figs. B, B 1, Plate V., p. 33). These drawings may be taken as representing also the size and shape of the tunnels in the former nest, which were for the most part like these, beautifully cylindrical, as is shown in the front view of the tunnel at B 1. In one nest of _barbara_ I found a curious hollow spherical dome, about an inch in diameter, the walls of which were constructed of hardened earth about two lines thick, and having a large circular aperture at the top and a very small one below (Figs. D and D 1, Plate VI.). This dome was imbedded below in earth which adhered to it, but it was otherwise easily separable from the soil; its inner walls were smoothed with great nicety.

It has been suggested to me that this spherical chamber was originally the work of a scarabæus, which had chanced to bury the ball containing its eggs close to the nest of the ants, and that the latter had appropriated it after the departure of the beetle grubs. This may perhaps have been the case, but the dome was rather larger than the ball usually formed by the scarab beetle, and I have never seen one of these balls surrounded by a hardened case. The chamber thus constructed was employed as a granary, and filled, as well as the adjacent passages, with the grain of a grass (_Tragus racemosus_), still enclosed in the husks, among which I detected several ants at work, and also some minute white semi-transparent creatures, like spring-tails (_Podurus_), which abound in these ants' nests. Besides this spring-tail it is common to find in the galleries and granaries of _Atta structor_ and _A. barbara_, certain silky yellowish-white "silver fish" (_Lepisma_), a small white woodlouse which does not roll itself into a ball, and at times the larvæ of an elater beetle. I have observed on more than one occasion that when in digging into an ant's nest I have thrown out an elater larva, the ants would cluster round it and direct it towards some small opening in the soil, which it would quickly enlarge and disappear down. At other times, however, the ants would take no notice of the elater, and it is my belief that the attentions paid to it on former occasions were purely selfish, and that they intended to avail themselves of the tunnel thus made down into the soil, with a view of reopening communications with the galleries and granaries concealed below, the approaches to which had been covered up. I have frequently watched the ants make use of these passages mined by the elater on these occasions.

At one time I suspected that the elater larvæ might consume the seeds stored by the ants, and I therefore confined some of them in a tumblerful of earth and seeds; but at the end of three weeks, though the larvæ were strong and healthy-looking, I could not detect that any of the seeds had been touched, and even those which had sprouted remained uninjured. I have searched in vain for the beetles and staphylinidæ which are known to inhabit certain ant's nests. In one nest I found (on Dec. 28) a quantity of small spherical, egg-like galls, slightly larger than but resembling the fruit of _Fumaria capreolata_, spotted with pink-brown on a yellowish or greyish ground. There was a dark spot at the point at which the mature insect would emerge, and one did escape from the egg-like cocoon while I was watching, and proved to be a _Cynips_ of very small size, but furnished with a terrible dart for puncturing its prey.

It seems difficult to understand how it comes that these galls are systematically placed among the seeds, for it was evidently no chance occurrence, and I can only conjecture that the worker ants may have brought them in and stored them under the impression that they were really seeds! Even ants make mistakes, and of this I have given an example above (p. 19). Though I have frequently found colonies of several distinct species of ants inhabiting nests made in the earth traversed by the widespread galleries of _Atta structor_ and _barbara_, I have never detected any intermixture of species in the chambers of a nest,[31] and but rarely found even the galleries and entrance used in common by more than one species. On one occasion when opening a nest of _structor_ I cut through a colony of the tiny, large-headed, yellow ant _Pheidole megacephala_, lying in the midst of, though distinct from, the former. When, however, it chanced that one of the _structors_ fell from the crumbling earth into the midst of the _Pheidoles_, it was curious to see how fiercely it would be attacked, and with what terrified speed it would scamper off, without attempting any resistance, and often carrying two or three _Pheidoles_ hanging on to its legs.

[Footnote 31: Except in a few cases where I have seen one or two _structors_ in nests of _barbara_ and _vice versâ_, and in the curious instance to be mentioned below, where one colony consisted of nearly equal parts of _structor_, _barbara_, and the red-headed variety of _barbara_.]

Accidentally in this way battles do sometimes take place between ants of different species; but by far the most savage and prolonged contests which I have witnessed were those in which the combatants belong to two different colonies of the same species.

_Atta barbara_, _Formica cruentata_, _F. erratica_, and especially _Myrmica cæspitum_ may sometimes be seen fighting in this desperate fashion. Rival colonies of _Myrmica cæspitum_ often gather for the battle into dense masses three or four inches deep, and the place of conflict will be seen on the following day strewn with the dead, and this though the majority of the slain are carried off for food by the victors.

But the most singular contests are those which are waged for seeds by _A. barbara_, when one colony plunders the stores of an adjacent nest belonging to the same species, the weaker nest making prolonged though, for the most part, inefficient attempts to recover their property.

In the case of the other species of ant which I have watched fighting, the strife would last but a short time--a few hours or a day--but _A. barbara_ will carry on the battle day after day and week after week. I was able to devote a good deal of time to watching the progress of a predatory war of this kind, waged by one nest of _barbara_ against another, and which lasted for forty-six days, from Jan. 18 to March 4!

I cannot of course declare positively that no cessation of hostilities may have taken place during the time, but I can affirm that whenever I visited the spot, and I did so on twelve days, or as nearly as possible, twice a week, the scene was one of war and spoliation such as that which I shall now describe.

An active train of ants, nearly resembling an ordinary harvesting train, led from the entrance of one nest to that of another lower down the slope, and fifteen feet distant; but on closer examination it appeared that though the great mass of seed-bearers were travelling towards the upper nest, some few were going in the opposite direction and making for the lower. Besides this, at intervals, combats might be seen taking place, one ant seizing the free end of a seed carried by another, and endeavouring to wrench it away, and then frequently, as neither would let go, the stronger ant would drag seed and opponent towards its nest. At times other ants would interfere and seize one of the combatants and endeavour to drag it away, this often resulting in terrible mutilations, and especially in the loss of the abdomen, which would be torn off while the jaws of the victim retained their indomitable bull-dog grip upon the seed. Then the victor might be seen dragging away his prize, while its adversary, though now little more than a head and legs, offered a vigorous though of course ineffectual resistance. I frequently observed that the ants during these conflicts would endeavour to seize one another's antennæ, and that if this were effected, the ant thus assaulted would instantly release his hold, whether of seed or adversary, and appear utterly discomfited. No doubt the antennæ are their most sensitive parts, and injuries inflicted on these organs cause the greatest pain.

It was not until I had watched this scene for some days that I apprehended its true meaning, and discovered that the ants of the upper nest were robbing the granaries of the lower, while the latter tried to recover the stolen seeds both by fighting for them and by stealing seeds in their turn from the nest of their oppressors. The thieves, however, were evidently the stronger, and streams of ants laden with seeds arrived safely at the upper nest, while close observation showed that very few seeds were successfully carried on the reverse journey into the lower and plundered nest.

Thus when I fixed my attention on one of these robbed ants surreptitiously making its exit with the seed from the thieves' nest, and having overcome the opposition and dangers met with on its way, reaching after a journey which took six minutes to accomplish, the entrance to its own home, I saw that it was violently deprived of its burden by a guard of ants stationed there apparently for the purpose, one of whom instantly started off and carried the seed all the way back again to the upper nest.

This I saw repeated several times.

After March 4 I never saw any acts of hostility between these nests, though the robbed nest was not abandoned. In another case of the same kind, however, where the struggle lasted thirty-one days, the robbed nest was at length completely abandoned, and on opening it I found all the granaries empty with one single exception, and this one was pierced by the matted roots of grasses and other plants, and must therefore have been long neglected by the ants. Strangely enough, not one of the seeds in this deserted granary showed traces of germination.

No doubt some very pressing need is the cause of these systematic raids in search of accumulations of seeds, and there can be little doubt that the requirements of distinct colonies of ants of the same species are often different even at the same season and date. Thus these warring colonies of ants were active on many days when the majority of the nests were completely closed; and I have even seen these robbers staggering along, enfeebled by the cold, and in wind and rain, when all other ants were safe below ground. It may be that unusual exertions are necessitated by some exceptional demands made by the condition of the larvæ of the winged male and female ants, and I have observed that these latter appear at very various periods. Thus I have seen winged males and females in the nests of _barbara_ on November 10, December 6, February 2, and March 10; and in those of _structor_ on February 23, 29, March 13, and April 6.

Though _structor_ and _barbara_ make seed collecting the business of their lives, they will, at least in times of scarcity, eagerly devour animal food if it happen to fall in their way, and in the harvesting trains a few ants may occasionally be seen carrying small dead insects and the like. Once I threw a dead grasshopper down close to a nest of _barbara_; it was immediately seized upon, and--after strenuous efforts had been made to dismember it above ground, some ants straining back the legs and wings, while others rushed in to gnaw at the muscles where the tension was greatest,--carried down below. On the following morning the wings of the grasshopper were to be seen on the rubbish heap in front of the nest. Dead house-flies and the larvæ of bees or wasps were at times readily devoured by my captive ants (_barbara_). I have also seen large numbers of _structors_ engaged in picking the bones of a dead lizard, and was once a witness of the following singular contest between a soft-bodied, smooth, greyish caterpillar, exactly an inch in length, and two medium-sized _barbara_ ants. The ants were mere pigmies in comparison of their prey, for as such I believe they regarded the caterpillar, but they gripped its soft body with set mandibles, showing the most savage determination not to loose their hold.

When I first detected the group the war was being waged in a tuft of grass over one of the entrances to the ants' nest, and the caterpillar was striding along the leaves, or thrusting itself between the culms in the hope to shake off or brush away its little persecutors. From time to time the caterpillar would turn viciously round and endeavour to pluck away its assailants, but though it actually succeeded in stripping off by means of its forelegs and mouth five of the six legs of one of the ants which was within its reach, they never once released their hold.

At length a chance movement of mine shook the grass leaf on which they were, and ants and caterpillar rolled together down a steep and rocky slope to about four feet distant. They tumbled over and over several times, but still the ants gripped their prey as firmly as ever.

The last endeavour of the giant victim was to rub off the ants by burrowing into the soil, but on uncovering its retreat, I saw that their positions were still the same. After watching this struggle for twenty minutes, time failed me, and I returned home, carrying with me, however, the combatants; and when on my return I opened the box in which they were imprisoned, these bull-dog ants were clinging with mandibles locked as firmly as ever, and now as I write, in death they are clinging still, drowned in a sea of spirits of wine.

During the winter and spring I kept two colonies of _barbara_ captive in the house, placed in separate glass jars, each of which might perhaps hold half a gallon. The former of these colonies was taken on December 18; but neither the queen ant nor larvæ were found, though there probably were larvæ in some unexplored part of the nest, and the ants were always restless and miserable, unceasingly trying to escape, and dying in large numbers.

On February 12 I found that all these ants, though abundantly supplied with seeds and all other kinds of food, were dead. Two other colonies of ants, however, which had been taken in a torpid state in the masses of earth which formed part of the original nest, were alive and well, though still torpid.

The second captive colony, taken on December 28, with the wingless queen ant and quantities of larvæ, formed a strong contrast with the previous one. Here the ants at once set to work upon the construction of galleries and safety places for the larvæ below the even surface of garden mould on which I had placed them within the jar; for in this case I did not attempt to preserve any portion of their own nest. This was done at 3.30 P.M., and by 9 that evening I found the ants most busily at work, having in less than six hours excavated eight deep orifices leading to galleries below, and surrounded these orifices by crater-like heaps, made of the earth pellets which they had thrown out. I have observed somewhat similar structures raised by _barbara_ after the nests have been closed on account of rain, and _structor_ frequently raises still more elaborate and distinct craters, such as those represented at Fig. B, Plate II., p. 22 (reduced one-half).

On the following morning the openings were ten in number, and the greatly increased heaps of excavated earth showed that they must probably have been at work all night. The amount of work done in this short time was truly surprising, for it must be remembered that, eighteen hours before, the earth presented a perfectly level surface, and the larvæ and ants, now housed below, found themselves prisoners in a strange place, bounded by glass walls, and with no exit possible.

It seems to me that the ants displayed extraordinary intelligence in having thus at a moment's notice devised a plan by which the superabundant number of workers could be employed at one time without coming in one another's way. The soil contained in the jar was of course less than a tenth part of that comprised within the limits of an ordinary nest, while the number of workers was probably more than a third of the total number belonging to the colony. If therefore but one or two entrances had been pierced in the soil, the workers would have been for ever running against one another, and a great number could never have got below to help in the all-important task of preparing passages and chambers for the accommodation of the larvæ. These numerous and funnel-shaped entrances admitted of the simultaneous descent and ascent of large numbers of ants, and the work progressed with proportionate rapidity. After a few days only three entrances, and eventually only one remained open. Yet for weeks this active work went on, and the ants brought up such quantities of earth from below that it became difficult to prevent them from choking up the bottle containing their water, which they repeatedly buried up to the neck. On January 10 the surface of the earth was raised from an inch and a half at its lowest, to three inches at its highest point above its original level, and this bulk of excavated earth represented the amount of space contained in their galleries and chambers constructed below. It was not, however, until nineteen days after their capture that the ants began to form systematic trains to carry down the seeds which I placed for them on the surface, and I suppose that they had required this time for the construction and consolidation of the granary chambers. From this time forward the ants came out repeatedly in greater or less force to gather in the various seeds with which I supplied them. Indeed, throughout the whole of their captivity they seemed to be perfectly contented with their lot and free from disease, remarkably few ants dying or appearing feeble, and as far as the limited space would permit they reproduced most of the habits which I had noted as belonging to them in a wild state, such as the formation of a rubbish heap; bringing out refuse materials, gnawed and empty seed-coats, the ends of radicles, and root fibres which had penetrated their nest, and laying sprouted seeds in the air to dry after having gnawed off the radicle in order to arrest their growth.

I was also in this way able to see for myself much that I otherwise could not have seen. Thus I was able to watch the operation of removing roots which had pierced through their galleries, belonging to seedling plants growing on the surface, and which was performed by two ants, one pulling at the free end of the root, and the other gnawing at its fibres where the strain was greatest, until at length it gave way. Again the habit of throwing sick and apparently dead ants into the water, the object of which was in part, I imagine, to be rid of them, and partly perhaps with a view to effecting a possible cure, for I have seen one ant carry another down the twig which formed their path to the surface of the water, and, after dipping it in for a minute, carry it laboriously up again, and lay it in the sun to dry and recover; thirdly, the stripping off the coats and husks of seed and grain swelling and on the point of sprouting, previous to eating it; and finally, the actual eating of the contents of the seed.

Most of these operations are usually performed below ground, and even in my captive nest it was but rarely that I could get a glimpse of their subterranean life, as they avoided the glass as much as possible, though it was carefully covered with flannel and black paper; and it was only by having the nest constantly before me on my table, and thus becoming a witness of their operations day and night during four months, that I detected them in positions which permitted me to watch these actions of theirs.

The ants were in the habit of coming out in numbers of an evening to enjoy the warmth and light of my lamp, and it was on one of these occasions that I first observed them in the act of eating. I perceived that in the midst of the black mass of ants gathered together on the side of the glass jar one was holding up a white roundish mass about as big as a large pin's head. Having turned a stream of bright light passed through a condenser on this group, and being permitted by the ants to make free use of my pocket lens, I was able to see the details with great precision. The white mass appeared to be the floury portion of a grain of millet, and I could see that two or three ants at a time would scrape off minute particles with their toothed mandibles, and take them into their mouths, repeating the operation many times, before giving place to other ants, and often returning again. It certainly appeared to be a _bonâ fide_ meal that they were making, and not merely an act performed for the benefit of the larvæ, as when they detach crumbs from a piece of bread and carry them below into the nest. However, I must own that, though I subsequently dissected ants taken in this act, which I suppose to be that of eating, I was unable by the use of the iodine test to detect starch grains in their stomachs.

Still it seems quite possible that this failure may have been due to my not having allowed the ants sufficient time to swallow their food, as I killed them almost immediately after disturbing them at their meal.

After having twice observed the ants eating as above described, I made some experiments in feeding them myself.

They immediately seized and set to work upon a minute ball of flour which I cut out from the centre of a grain of millet, taken from a heap in front of a nest of _A. structor_, which had begun to sprout and been deprived of its radicle and dried. A similar ball taken from a sprouting grain of millet, but the growth of which had not been arrested, was also partially eaten; but the hard, dry flour taken from a grain of the same in its natural state, not moistened, was at once rejected and thrown on the rubbish heap. The fat, oily seed leaves of the hemp, however, were eagerly taken, though not softened by water, their peculiar texture allowing the ants to scrape off particles, as in the case of the ball of flour of the sprouted millet. Under ordinary circumstances the hard shell of the hemp-seed, and the coats of most other small fruits, grain, and seeds, would prevent the ants from getting at the contents while dry, but in the earliest stage of sprouting the shell parts of itself, allowing the radicle to protrude, and then they find their opportunity. (See Figs. A, A 2, Plate VI., p. 35.)

It has always been supposed that ants, from the delicate nature of their mouth organs, were only able to lap up liquids or to swallow very soft animal tissues, and one of the great difficulties in the way of admitting that they might collect seeds for food, lay in the apparent impossibility of their eating such hard substances. But it has generally been overlooked that not only are all seeds soft when moistened with water and ready to grow, but also that there are certain kinds of seeds the contents of which are naturally soft.

The most important organs in an ant's mouth are shown in Fig. D 2, and D 3, in Plate I., p. 21. D 3 represents one of the horny, toothed mandibles, which serve admirably for scraping off particles of flour from the seeds. Within these are the parts shown at D 2, where the outermost pieces are the maxillæ and their four-jointed palpi or feelers, and the innermost piece the labium and its three-jointed palpi, between which the end of the delicate membranous tongue appears.

I repeatedly placed leaves from the orange trees covered with cocci and aphides from rose-bushes and pine trees, all of which are eagerly sought by several other kinds of ants, in the captive nest, but the ants never looked twice at them, and this corresponds with the fact that I have never seen either _structor_ or _barbara_ attending on or searching for aphides and the like. These captives took part of a small quantity of honey which I placed in the nest, but displayed no eagerness about it, and soon neglected and allowed it to be covered up with earth thrown out from the nest.

The ants work very frequently at night during the dark,[32] and this is the case in the wild as well as in the captive nests. A friend, at my request twice visited a nest of _structor_ ants in the garden of an hotel at Mentone, when it was quite dark (in March, between seven and eight o'clock P.M.) and no moon, but the light of a candle showed that the workers, both large and small, were busily engaged in carrying into the nest seeds which had been purposely scattered in their neighbourhood. I have myself seen _Pheidole megacephala_ similarly engaged at about nine P.M. on a warm night in April, when it was perfectly dark, not even the stars showing; but in this case the ants were collecting from the weeds in the garden. On the same occasion I also observed long and active trains of _Formica emarginata_ [a rather small dusky ant, with a yellow thorax], making for the orange-trees in search of cocci and aphides, just as if it were broad day.

[Footnote 32: This bears out the much-questioned assertion of Aristotle, though he only claimed that ants work "by night when the moon is at the full."--Hist. Anim., lib. ix. cap. xxvi.]

Before leaving Mentone, on May 1, I turned out this second captive nest, and found that the colony appeared perfectly healthy, and did not seem to have diminished materially in numbers. The queen ant and the larvæ seemed to be in just the same state as when they were taken. The earth in the lower part of the jar was honeycombed with galleries, granaries, and cells, constructed quite as in the wild nests, but more crowded together. The granaries were in many instances full of seeds, which, though very wet, [the surrounding soil being extremely moist on account of there being no drainage to carry off the water which I was obliged to sprinkle from time to time over the surface of the nest], still showed no trace of germination that I could detect. The ants were therefore able to exercise the same influence over these seeds, under the strange conditions of their captive state, that they do in their natural homes.

The foregoing remarks, as has been stated above, refer for the most part to only one of the three kinds of harvesting ants which I have observed on the Riviera--that is to say, to _Atta barbara_, the jet-black ant.

As far as the manner of collecting and storing the seed is concerned, all that has been said of _Atta barbara_ applies with equal truth to _A. structor_.

_A. structor_ is, however, less frequently seen above ground from December to March than _barbara_, and is more frequently found in or near the streets and gardens of a town.

The fourth species, on the other hand, the little _Pheidole megacephala_, differs in several particulars. This ant appears to shun the daylight, and to be most active at night, when, in the warm weather at the end of April, it may frequently be seen carrying large quantities of seeds into its nest. I have rarely observed it at work in the daylight, so that my knowledge of its habits is but small. Nor have I succeeded in discovering its subterranean granaries, though I have opened several nests. Still, I believe that it is a true harvesting ant, and not merely a casual collector of seeds. Of the habits of _Pheidole pallidula_, a very closely allied and similar species, but one less frequently met with, I cannot speak with certainty, though it is quite possible that it also may be a true harvester, in which case it would add a fifth species to this class.

Both _Pheidole megacephala_ and _Ph. pallidula_ appear to remain inactive, or nearly so, during the months from November to April, and it is probable that they are only to be seen in full activity during the summer when I am not there to watch them.

There can be little doubt that any naturalist who will take the pains to note the habits of ants on the shores of the Mediterranean through June, July, August, and September, might collect a most interesting series of observations on harvesting and other species, and add to, and perhaps modify, those which my limited opportunities have enabled me to make.

There are three other ants[33]--namely, _Formica emarginata_, _F. fusca_, and _Myrmica cæspitum_, which may also occasionally be found carrying a few seeds, but this is the rare exception, as far as my experience goes, these species living on honey dew, sweet secretions, and animal matter, like the great majority of ants all over the world. I have never found seeds in the nests of any ants except those of _Atta barbara_ and _A. structor_, though I have carefully searched for them in most of the nests of the sixteen species of ants whose habits I have watched.

[Footnote 33: For some details of the habits of the sixteen species of ants observed on the Riviera, see Appendix A.]

There is every probability that these harvesting ants will be found all round the shores of the Mediterranean, but the only points at which I have positively heard of the existence of the habit besides Mentone, Cannes, and Marseilles, are Capri[34] and Algiers. I am indebted to Miss Forster for having, during a short visit to Algiers, devoted some time to watching the habits of the ants in a garden at that place. These observations were made in April last (1872), when the three following species were watched:--

[Footnote 34: Where a harvester, probably _Atta barbara_, has been observed by Mr. Buchanan White. See Appendix C.]

(1) _Formica (Cataglyphis) viatica_, a large, long-legged, blackish ant, with orange-red and semi-transparent thorax, which never carried seeds, but lived on animal food, especially flies. (2) _Formica (Tapinoma) nigerrima_,[35] a rather small dusky ant, which brought in some seeds to its nest, but principally "animal food, flies, small worms," &c., and which did not carry the hemp and canary seed strewed in their path, though on one occasion when Miss Forster scattered some split hemp seed, they eagerly fastened upon the contents, and ate some on the spot, while they transported the greater part to their nest, and (3) _Atta barbara_, which, as on the Riviera, was a true and most active harvester, and eagerly seized upon the hemp and canary seed when these were placed in its way.

[Footnote 35: Mr. Smith thinks that this ant is either _F. nigerrima_, of Nylander, or a new species, but it was not possible for him to pronounce with absolute certainty as he had only two specimens of workers from which to judge.]

_Recapitulation and Concluding Remarks._

There are some points of interest suggesting openings for future observation, to which I will now allude, making at the same time a partial recapitulation of what has gone before.

We have learned in the first place that the ancients had facts on their side when they said that the ant is one of the very few creatures which lays up supplies of food sufficient to last for months, or even perhaps, as Bochart says, for a whole year; and though we cannot quite accept the statement that "there is no animal except men, mice, and ants, that stores its food,"[36] they were right in saying that the habit is a most singular and interesting one. It is probable, however, that the old writers may have fallen into the error of supposing that all ants were harvesters, though the truth appears to be, that even in hot climates, it is only a very small number of species that are so. The fact that certain ants in Southern Europe do store large quantities of sound seed in damp soil, and check their tendency to germinate, may be thought to favour the possibility of the existence of those deeply hidden supplies of seed which, though they have never been detected, are popularly supposed to explain the sudden appearance of the crops of weeds on soil newly brought out from great depths.

[Footnote 36: Sophian, quoted by Bochart in his Hierozoïcon, ii. cap. xxi, p. 497.]

The argument may be stated thus: seeds remain for months undecayed, and still capable of germination, at depths varying from one to twenty inches below the surface of the soil in certain ants' nests, why should they not lie hidden for indefinite periods in ordinary soil?

To answer this positively, experiments should be made[37] in order that we might learn whether these seeds can retain their vitality without sprouting in moist soil; but the general belief is that under these conditions they will do one of two things, they will either grow or rot. Be this as it may, one of the most curious points that we have learned about these ants, is that they know how to preserve seeds intact, even when within from one to three inches of the surface of the ground, that is to say, at the actual depth at which a gardener most frequently sows his seeds, though if these very seeds are taken out of the granary and sowed by hand, they will germinate in the ordinary way. It is possible that this may be in part due to the compact nature of the floors and ceilings of the granaries, these excluding air in some measure, though as moisture freely passes through them, and there are always two or three open galleries leading into the granaries, and which communicate directly with the open air, I can scarcely accept this explanation as complete.

[Footnote 37: In order to try the experiment fairly, seeds taken from ants' nests, or seeds of the same species as those which are habitually found in ants' nests, should be placed at different depths in the earth and examined after the lapse of six or eight months.

Why it is that certain seeds resist the influences which destroy the vitality of other seeds of closely allied species is another and a very curious but complicated problem, the explanation of which may perhaps lie in the different chemical properties of the seeds in question, in the more or less permeable character of their seed-coats, or their general texture.]

The seeds do occasionally sprout in the nest, though it is extremely rare to find instances of this, and then the ants nip off the little root, and carry each seed out into the air and sun, exactly as the old writers have described, and when the growth has been checked and the seed malted by exposure, they fetch them in again. It is in this condition that the ants like best to eat them, as I have proved by experiments among my captives.

As the ants often travel some distance from their nest in search of food, they may certainly be said to be, in a limited sense, agents in the dispersal of seeds, for they not unfrequently drop seeds by the way, which they fail to find again, and also among the refuse matter which forms the kitchen midden in front of their entrances, a few sound seeds are often present, and these in many instances grow up and form a little colony of stranger plants. This presence of seedlings foreign to the wild ground in which the nest is usually placed, is quite a feature where there are old established colonies of _Atta barbara_, as is shown at Fig. A in Plate I., p. 21, where young plants of fumitory, chickweed, cranesbill, _Arabis Thaliana_, &c., may be seen on or near the rubbish heap.

It would be interesting to make a list of all these ant-imported plants, and I think it quite likely that, if a sufficiently large number of nests were visited, some seedlings of cultivated species might be found amongst them, for we have seen that garden plants are frequently put under contribution.

One can imagine cases in which the ants during the lapse of long periods of time might pass the seeds of plants from colony to colony, until after a journey of many stages, the descendants of the ant-borne seedlings might find themselves transported to places far removed from the original home of their immediate ancestors. It is a true cause, but at the same time it may be one which has, like many true causes, exceedingly small effects. One can scarcely look at the teeming population of an ant's nest, without asking whether there are any checks to their increase, and if so, what these checks are. I know very little of what foreign enemies they may have, though I have occasionally seen them captured by lizards, _Cicindela_ beetles, and spiders,[38] and it is well known that the females are eagerly sought for by birds at the season when they are above ground, and about to found new colonies; but I believe that ants are the ants' worst enemies, for fearful slaughter and mutilation often result from the encounter of armies of the same race, but belonging to different nests.

[Footnote 38: I have seen the remains of ants at the bottom of the tube of trap-door spider nests, and watched a hunting spider, _Lycosa_, capture a large black ant (_Formica pubescens_), by entangling it in threads, which it deftly spun about its limbs, while running rapidly round the struggling victim in a circle, and dodging out of the way of the ant's mandibles. In England one may frequently see ants caught in the spiders' webs among the rose-bushes, and Mr. Blackwall says, in his Spiders of Great Britain and Ireland, that _Theridion riparium_ lives principally on ants.]

Harvesting ants have nothing to do, as far as I have been able to discover, with aphides, cocci, and the like, nor do they seek for any of those sweet secretions which are the staple food of the generality of ants; they live, however, on very friendly terms with certain yellowish-white and satiny-coated "silver-fish" (_Lepisma_), which are found in the passages and chambers of the nests; but what their relations are to these creatures and to certain beetles which have been found in the nests of _Atta barbara_ in Spain and Syria is unknown. It is possible that by carefully watching captive ants in company with these creatures under very favourable conditions, something further might be learned on this head. My captive ants constructed all their chambers, granaries, and almost all their galleries away from the glass, and in the interior of the earth, though I tried to tempt them to work in parts more accessible to sight by swathing the jar in flannel.

There is much to be learned, I do not doubt, about the friends and enemies of harvesting ants; and another great desideratum is further information as to the parts of the world in which they are found and what causes may be assigned for the limitation of the habit.

What is the geographical distribution of the harvesting species, and what the geographical distribution of the habit? For instance, to quote Mr. F. Smith,[39] _Atta structor_, though not "found in England, is scattered over a great part of Europe, having occurred in France, Italy, Germany, Austria, Dalmatia, and Switzerland; it has also been found in Algeria" and Syria; and _A. barbara_ is almost as widely spread. May we then conclude that these species are harvesters wherever they are found, and that they store seed in Germany and Switzerland as freely as they do on the shores of the Mediterranean? If this be really so, then Huber, whose attention was specially directed to this point, and a host of laborious and scrupulous observers of the Continent, have had the very fact under their eyes, though they have been at considerable pains expressly to deny it. I cannot think that this is likely, but it is a matter which could easily be settled by those who travel or reside in Germany, Northern France, or Switzerland.

[Footnote 39: Mr. F. Smith, On Some New Species of Ants from the Holy Land, in Journ. Linnean Soc., London, vol. vi. p. 35.]

It seems to me more probable, however, that they do store in the south, but not in the north; for all the difficulties which attend the preservation of the seed in the granaries in the south would be greatly increased in the wet climates of Northern Europe, and there, moreover, the greater cold would render the ants torpid almost throughout the winter, when food would not be required. But the question is plainly an open one. We may also ask why it is that only a very few out of the many species of ants which inhabit the shores of the Mediterranean should possess this habit of collecting seeds, and differ so widely in their manner of living, from their neighbours?

If we wish to put ourselves in the way to answer these queries, the first thing we should do would be to examine and compare the structure of the digestive organs and parts of the mouth in harvesters and non-harvesters, with a view to seeing whether there may not be some capital difference here.

These observations demand some skill in dissection and preparation, and in regretting that it has not been in my power to make them, I can only hope that some one more skilled than I am may undertake the subject.

It seems probable, that in warmer latitudes there are many conditions which favour the rapid increase of ants, so that a given tract of country in Southern Europe, for example, must have on an average more colonies to support than a similar tract in the north, and that to meet this increase of population, it has therefore become necessary for these creatures to seek their subsistence from as many and as dissimilar sources as possible. The fierce conflicts over booty both between rival nests of the same and of distinct species, tend to show that, even as things are, they frequently have to fight for their food.

Hitherto, as far as I have been able to learn, only nineteen true harvesting ants have been detected in the whole world, limiting this term to those species which make the collection of seeds the principal occupation of their outdoor lives, and are evidently in the main dependent upon this kind of food for subsistence.

Now if we compare these nineteen species of ants[40] together a very curious fact forces itself upon our notice--namely, that all of them are closely related, so much so that not only do all belong to the same division of ants (the tribe _Myrmicineæ_), but that with one exception (_Pseudomyrma_) all would have been placed by the great Fabricius in one genus, _Atta_, and the one exception is not far removed from it.

[Footnote 40: These are _Myrmica (Atta) barbata_, from Texas and Mexico; _Œcodoma (Atta) cephalotes_, from Brazil and Mexico; _Œcodoma (Atta) providens_, from India; _Œcodoma (Atta) diffusa_, from India; _Atta rufa_, from India; _Pheidole (Atta) megacephala_, from South France; _Atta barbara_, from South France, Capri, and Algiers; _Atta structor_, from South France; and _Pseudomyrma rufo nigra_, from India.]

We must not forget, however, that, as has been stated, there are other ants which do occasionally collect seeds, and thus appear to show traces of this remarkable instinct; but as far as I have yet seen, it is always possible to distinguish them readily from true harvesters. Still I think it very likely that in hot climates the division between harvesters and non-harvesters may be bridged over by a complete chain of intermediates. Here two more questions suggest themselves for more complete future solution. (1) Do true harvesters which store seed in granaries ever attend upon aphides and seek for sweet secretions? (2) Do occasional harvesters ever form granaries?

In any case the name of "the provident one" is only, I suspect, fully deserved by a limited number of ants, and Æsop, in his well-known fable, might as properly have made the dialogue which ends in the recommendation to "dance in winter as he piped in summer," take place between two ants as between an ant and a grasshopper, as far at least as their respective foresight is concerned.

Why it is that one ant should require stores of food in the winter of which other ants have no need, is one of the many problems which only patient watching and careful comparison and experiment can help us to solve.

There are not wanting those among the many winter visitors of the south who have time in abundance or superabundance at their disposal, and might help to clear up these and many other mysteries, and to them I would strongly recommend the study of the habits of plants and animals as a pastime, if nothing more.

The way is open: it is not difficult to follow, and it leads to very pleasant places.