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HARVESTING ANTS.

PART I.

HARVESTING ANTS.

It was in May, 1869, that Mr. Bentham in his presidential address to the Linnean Society called attention to the want of reliable information as to the existence of such subterranean accumulations of seeds as are popularly supposed to account for the sudden appearance on railway cuttings, gravel from deep pits, and the like, of crops of weeds hitherto unknown in a district.

He suggested that it might repay the trouble if some accurate observers were to take this in hand, and investigate the matter both by examining samples of undisturbed soil taken from various depths,—when, if any seeds of moderate size were present and undecomposed, it would be tolerably easy to distinguish them,—and also by ascertaining what means of transport exist by which seeds may be scattered over exposed surfaces, and thus explain the difficulty without having recourse to hypothetical supplies of sound though long-buried seeds.[1]

[1] M. Kerner of Innspruck has lately adduced some facts bearing on the question of the transport of seeds by the wind, having examined the collections of animal and vegetable substances found on the icy surfaces of glaciers and the plants growing on moraines. Judging from the facts thus obtained, he attributes but a small influence to this agency, as the specimens discovered belonged to the fauna and flora of the immediate vicinity, and not one of these specimens must needs have come from a distance. See abstract of his paper in Gardener's Chronicle, Feb. 3, 1872, p. 143, and in 'Nature' for June 27, 1872, p. 164.

As I listened, the question occurred to me whether the ants, which I had observed carrying seeds to their nests at Mentone, might not be unconscious agents on a small scale, both in the distribution and the subterranean storing of seeds. When at a later time I made this suggestion to some of our leading naturalists, I learned with considerable surprise that the unanimous opinion of our highest modern authorities on the subject is opposed to the belief that European ants ever do systematically collect and make provision of seeds, and that the instances of such occurrences in tropical climates remain as isolated though undoubted facts which it is difficult to explain.

I was not then aware that towards the middle of last century the ancient belief, dating from the time of Solomon, that ants habitually show forethought and husbandry in the collection of supplies of seeds and grain had begun to be called in question, and that our most able observers, such as Huber, Gould, Kirby and Spence, and at the present day Mr. Frederick Smith, had by close scrutiny of the habits of these creatures proved that, wherever personal investigation had enabled them to put the matter to proof, no trace of harvesting was found.[2]

[2] I have myself on many occasions thrown seeds in the track of the common English ants, and my experience was, up to the past summer (1872), similar to that of the above-named naturalists, but I have lately, by the merest chance, become acquainted with a curious exception to this rule. It happened as follows. I was gathering some fresh capsules of the common sweet violet in a garden at Richmond, near London, and in pouring the seeds out of my hand into the paper bag made to receive them, a few were spilled on the ground. In a short time afterwards I was greatly surprised to see some of these spilled seeds in motion, being carried by the common black ant (Formica nigra) into its nest. On seeing this I hastened to get some more fresh violet seeds, and also a quantity of seeds taken from ant's granaries at Mentone, and scattered these where the other seeds had lain. After watching for half an hour a few of the violet seeds were carried in, but not one of the granary seeds was removed, though these were examined with some curiosity. I repeated this experiment twice afterwards on a distinct colony of ants of the same kind and obtained exactly the same result. I opened the nest of the former colony on the day after they had carried in the seeds, but failed to find these or any stores of other seeds.

I am inclined to think that the ants took these seeds believing them to be larvæ of other ants which they might eat; for fresh seeds of violet are not very unlike the larvæ of certain ants, as, for example, those of Atta barbara, figured at Plate I., Fig. E., p. 21, the semi-transparent membranous appendage partly concealing the seed and giving it a fleshy appearance.

I think this the more likely because on two occasions the seeds which had been carried into the nest were subsequently thrown out by the ants, which had I believe discovered their mistake.

However, just as the ancient writers, judging from their own experience and from the reports of others, had erred in attributing to ants in general the habit of seed-storing possessed by certain species commonly found in the south, so have modern naturalists fallen into the mistake of denying it to any of the European species.

The older authors who lived in Greece and Italy, and the mediæval authors who drew their information in great measure from the former, being familiar with the fact that some ants habitually collect large supplies of seed, went so far as to assert, or to imply, that all European ants do so; the authors of the present day, on the other hand, generalizing too freely from their experience of ants found near their northern homes, maintained and maintain the very reverse.

So long as Europe was taught natural history by southern writers the belief prevailed; but no sooner did the tide begin to turn, and the current of information to flow from north to south, than the story became discredited.

It is interesting now to recall a few of the allusions to the harvesting ants made by ancient authors, some of which contain tolerably accurate accounts of what was to them a familiar sight or a universally accepted fact.

The passages in Proverbs[3] are the following: "Go to the ant, thou sluggard: consider her ways and be wise; which, having no guide, overseer, or ruler, provideth her meat in the summer, and gathereth her food in the harvest." "The ants are a people not strong, yet they prepare their meat in the summer." Hesiod[4] speaks of the time

"When the provident one (the ant) harvests the grain."

ὅτἐ τ ιδρις σωρὀυ ἁμαται.

[3] vi. 6-8 and xxx. 25.

[4] Works and Days, 776.

Horace[5] also alludes to the foresight of the ant, who is "haud ignara ac non incauta futuri." Virgil[6] compares the Trojans hastening their departure to harvesting ants, and the passage has been thus rendered by Dryden:—

T' invade the corn, and to their cells convey

The plundered forage of their yellow prey.

The sable troops, along the narrow tracks,

Scarce bear the weighty burden on their backs;

Some set their shoulders to the ponderous grain;

Some guard the spoil; some lash the lagging train;

All ply their several tasks, and equal toil sustain."

[5] Satires I. i. 33.

[6] Æneid, Bk. iv. l. 402.

"The beach is covered o'er

With Trojan bands, that blacken all the shore:

On every side are seen, descending down,

Thick swarms of soldiers, loaden from the town,

Thus, in battalia, march embodied ants,

Fearful of winter, and of future wants,

"Ac velut ingentem formicæ farris acervum

Quum populant, hiemis memores, tectoque reponunt:

It nigrum campis agmen, prædamque per herbas

Convectant calle angusto; pars grandia trudunt

Obnixæ frumenta humeris; pars agmina cogunt,

Castigantque moras; opere omnis semita fervet."

Indeed, it would seem that among the people inhabiting the shores of the Mediterranean it was almost as common to say "as provident as an ant" as it is with us to say "as busy as a bee." Plautus[7] introduces a slave who, when attempting to account for the rapid disappearance of a sum of money of which he had charge, says,

"Confit cito

Quam si tu objicias formicis papaverem."

"It vanished in a twinkling,

Just like poppy seed thrown to the ants."

[7] Trinummus, Act ii. sc. 4, l. 7.

Any one who has seen the eagerness with which certain southern ants seize upon seeds thrown in their path will appreciate the correctness of this simile.

Claudius Ælianus, who lived in the time of Hadrian, gives a detailed account of the habits which he attributes to ants,[8] from which the following is a translation: "In summer time, after harvest, while the ears are being threshed the ants pry about in troops around the threshing floors, leaving their homes, and going singly, in pairs, or sometimes three together. They then select grains of wheat or barley, and go straight home by the way they came. Some go to collect, others to carry away the burden, and they avoid the way for one another with great politeness and consideration, especially the unburdened for the weight carriers. Now these excellent creatures, when they have returned home, and stored their granaries with wheat and barley, bore through each grain of seed in the middle; that which falls off in the process becomes a meal for the ants, and the remainder is unfertile. This these worthy housekeepers do, lest when the rains come the seeds should sprout, as they would do if left entire, and thus the ants should come to want. So we see that the ants have good share in the gifts of nature, in this respect as well as others." Further on[9] he gives a very interesting account of their mode of collecting and preparing the grain, many details of which I can myself substantiate from personal observation, though I have never seen ants actually at work upon the ears of corn. "But when the ants start a foraging, they follow the biggest, who take the lead as generals. And when they come to the crops, the younger ones stand under the stalk, but the leaders ascending gnaw through the culms, as they are called [ὀυραγοὑς, 'the stalk ends on which the ears grow' (Lid. and Scott, Gr. Lex.)], probably meaning that they detach the separate spikelets of which the ears are composed], of the ears [καρπἱμων], which they throw to the people below. These busy themselves with cutting away the chaff and peeling off the envelopes which contain and cover the grain. So the ants, though they need no threshing time, nor men to winnow for them, nor an artificial draught of wind to separate corn and chaff, yet have the food of men who both plough and sow for it." Ælian appears also to have heard reports of the habits of ants in tropical countries, for he says,[10] "Certainly the Indian ant is also a wise creature.... They leave one opening at the top (of the nest), by which they have their exits and entrances, when they come bearing the seeds which they collect." I have never myself found seeds bored through the centre in the way recorded above, but it is possible that different species of ants may treat the seeds in other ways than those observed by me; or, on the other hand, Ælian may have mistaken the gnawing off the radicle of the seed, a process which I shall describe from personal observation below, and imagined that the seed itself was pierced.

[8] Ælian, De Naturâ Animalium, ii. 25.

[9] Ælian, De Nat. Anim., lib. vi. chap. xliii.

[10] Id. lib. xvi. 15.

Aldrovandus, writing in the sixteenth century, speaks[11] of the ants as storing seed and of their gnawing, "illud principium seu acumen grani, è quo germen emitti à tritico solet"—that is to say, the radicle. But it is not clear whether Aldrovandus treats of what he has himself seen or refers to the account given by a certain Bishop, Simon Mariolus, who, he says "in his most pleasant and learned work, introduces a philosopher as taking his walks abroad and examining an ant's nest with its seed store," &c.

[11] Aldrovandus, De Insectis, lib. v. (de Formicis).

The lively fable of the ant and the grasshopper, as related by La Fontaine, has done much towards familiarizing and keeping alive in the minds of many of us the idea that ants habitually provide stores against the winter; but we must not infer from this narration that the witty French author had ever cared to examine for himself whether the fable, which he borrowed from Æsop, had its foundation in fact or not. The following translation from, the Greek original[12] bears in a much higher degree the impress of personal and accurate observation.

[12] For this translation and all the foregoing extracts from ancient and mediæval authors I have to thank my brother, M. W. Moggridge.

Μὑρμηκες καἰ Τἑττιξ: The Ants and the Grasshopper. Once in winter time the ants were sunning their seed-store which had been soaked by the rains. A grasshopper saw them at this, and being famished and ready to perish, he ran up and begged for a bit. To the ant's question, "What were you doing in summer, idling, that you have to beg now?" he answered, "I lived for pleasure then, piping and pleasing travellers." "O, ho!" said they, with a grin, "dance in winter, if you pipe in summer. Store seed for the future when you can, and never mind playing and pleasing travellers."[13] It would be easy to multiply instances in which the older authors allude to this habit, but enough have been given to afford a sample of what may easily be found repeated elsewhere, and I will now quote a few instances which illustrate the more modern belief, utterly opposed to that so long maintained by the ancients.

[13] Æsopicæ Fabulæ (Tauchnitz edition), p. 92.

Messrs. Kirby and Spence[14] discuss the matter in the following terms:—"When we find the writers of all nations and ages unite in affirming that, having deprived it of the power of vegetating, ants store up grain in their nests, we feel disposed to give larger credit to their assertions. Writers in general have taken ... (this) ... for granted. But when observers of nature began to examine the manners and economy of these creatures more narrowly, it was found, at least with respect to the European species of ants, that no such hoards of grain were made by them; and, in fact, that they had no magazines in their nests in which provisions of any kinds were stored up."

[14] Entomology, ed. 7 (1856), p. 313.

They then proceed to explain how easily the white pupæ, which the ants carry about in their jaws, may have been mistaken for grains of wheat, and to inform us that the accurate observations of Mr. Gould, published in 1747, were among the first which led to the correction of this error. "However," they continue, "it may be otherwise with exotic ants, for although during the cold of our winters they are generally torpid and need scarcely any food, yet in warmer regions, during the rainy seasons, when they are probably confined to their nests, a store of provisions may be necessary for them."

The author of the article on ants in Smith's Dictionary of the Bible says, in reference to the assertion that ants store seed, that "observation of the habits of ants does not confirm this belief."

Latreille[15] denies it in the following emphatic terms: "N'attribuons pas à la fourmi une prévoyance inutile: engourdie pendant l'hiver, pourquoi formeroit elle des greniers pour cette saison?"

[15] Hist. Nat. des Fourmis, 1802.

Huber again throws the weight of his great authority into the scale against the ants, when he says,[16] "I am naturally led to speak in this place of the manner in which ants subsist in the winter, since we have relinquished the opinion that they amass wheat and other grain, and that they gnaw the corn to prevent it from germinating." He then goes on to show how the ants are frequently torpid during the winter, and that when it happens that a few warmer days wake them up to life, they can always find a few aphides also on the alert; for, strange to say, the same degree of warmth which rouses the ants calls forth the aphides also. It would appear that ants in the northern parts of Europe feed on the honey-dew of aphides, and on animal matter when they can get it; and up to the present time the belief prevails among our modern naturalists that they are limited to the same diet in all parts of Europe.

[16] Huber, on Ants, translated by J. R. Johnson, 1820.

It is now well known, however, that exceptions must probably be made in tropical countries, for the observations of Lieut.-Col. Sykes[17] and Dr. Jerdon[18] have shown that many ants in India collect grain in large quantities, robbing the crops and plants cultivated in gardens, and even stealing seeds put away in drawers, the inference being that they employ them for food. The same observers have recorded how the ants may be seen after wet weather bringing out the grain to dry in the sun.

[17] Lieut.-Col. Sykes, Description of New Indian Ants, in Trans. Ent. Soc. Lond., i. 103 (1836), where a single species of ant, which he names Atta providens, is described, and its habit of harvesting recorded.

[18] Dr. Jerdon, Madras Journal Lit. and Sc. (1851), where three species are stated to harvest seeds on a large scale—namely, Œcodoma (or Atta) providens, Œcodoma diffusa, and Atta rufa, all of which belong to the same section of ants as our Mentonese harvesters, Atta barbara, Atta structor, and Pheidole (or Atta) megacephala. These very interesting observations of Dr. Jerdon's, as well as those of Lieut.-Col. Sykes, will be found in Appendix B.

Dr. Lincecum has also given a very interesting account[19] of the habits of the "agricultural ant" inhabiting Texas, Myrmica (Atta) barbata, which not only stores the grain of a particular rice-like grass, but is said to maintain a clean crop of this plant around its nest, suffering no weed to appear among it, and harvesting the crop in its proper season.

[19] Published in the Journal of the Linnean Society of London, vol. vi. p. 29. 1861.

The Sauba ant (Œcodoma cephalotes) has been seen by Mr. Bates plundering baskets containing mandioca meal (an impure form of tapioca) in Brazil, and this in so wholesale a manner as shortly to threaten the loss of the entire supply; and Dr. Delacoux records[20] the presence in New Granada of a monstrous ant, called by the natives Arieros, a word which, I am informed, is of Arabic extraction, and means the carrier, which emptied an entire sack of maize belonging to him in a single night.

[20] Notice sur les Mœurs et les Habitudes de quelques Espèces de Formiciens des Climats Chauds. Rev. Zool., Mai, 1848, p. 1849.

It seems strange that while travellers have reported the seed-storing habits of ants in far distant countries, our naturalists at home should have not only remained unaware of its existence in Europe, but even strenuously denied it. It is certain, however, that naturalists and others in southern Europe are more or less aware of the fact, but I have been unable to learn that any accurate account of the habits of harvesting ants has hitherto been published, or that any one has taken pains to discover what becomes of the seed so laboriously obtained.

It is true that in the Enciclopedia Popolare[21] extracts are given from the remarks made by M. Gené[22] on the subject, in which he assumes that the fact that ants collect and carry to their nest large supplies of grain and seed is well known, but states that he is at a loss to conceive how they employ them, unless it may be that they use them as materials for the construction of their galleries, for they cannot eat such hard substances, all their food being either liquid or of the nature of juices, "gli alimenti sono sempre materie liquide o materie sugose. Quanto ai corpi duri e secchi che le formiche raccolgono, io non so altrimenti riguardarli che come materiali di costruzione." It will be understood, I think, from what has gone before, that thus far nothing has really been ascertained as to the exact state of the case; for though the Italian author just quoted was aware that certain ants in the Mediterranean region do store seed, his knowledge went no further. Nor am I aware that any French author has published an account of this habit and its object; and in a recent abundantly illustrated volume founded on a work by M. Emile Blanchard, I find, on the contrary, the following very emphatic denial of its existence:—"The curious idea which appears to have commenced in very remote times, and to have been carried down by tradition, and which was assisted by the results of careless observations, concerning the habits of the ants in collecting and storing up provisions, as it were under the influence of a wise foresight, is evidently incorrect."[23] There was, therefore, clearly an opening here for close observation, and this I determined to do my best to supply.

[21] Article Formica, vol. v. p. 143-4. (Turin, 1845).

[22] Memorie per servire alla Storia Naturale di alcuni imenotteri, published at Modena, in 1842.

[23] The Transformations of Insects: an adaptation for English readers of M. Emile Blanchard's Metamorphoses, Mœurs, et Instincts des Insectes, p. 196. London. 1871.

When I set out again from England in October, 1871, on my way to Mentone, I had obtained an idea of some of the leading points which needed to be cleared up, and I was greatly encouraged in my attempt by the interest expressed in the subject by several of our leading naturalists, among whom I may especially mention Mr. Frederick Smith.[24]

[24] am very greatly indebted to Mr. Smith for much kind assistance, and especially for having named the specimens which I collected.

Plainly the first thing to do was to determine whether the seeds which I had watched the ants carry to their nests were separately stored in subterranean granaries, as they would be if the ant really provides for the future; or whether they were merely strewed here and there, or used as building materials.

Next I must, if possible, obtain conclusive evidence as to the use to which the ants put the seeds thus collected; whether they eat them or turn them to some other account. Again I must observe whether the seed-collecting ants also search for aphides, and what other kinds of food they obtain. Then another very interesting question remained—namely, whether all southern ants uniformly collect seed, and to the same extent, or whether the habit is peculiar to certain species.

These, and many other subjects of inquiry connected with them, readily suggested themselves to my mind, and it will now be my endeavour to show how far I have been able to throw light upon them.

The habits recorded in the following pages refer exclusively, unless special notice is given to the contrary, to Atta barbara, the black ant represented on Plate I. We have, as far as I am aware, only four bonâ fide harvesting ants on the Riviera—namely, Atta barbara under two forms, the one wholly black the other red-headed; Atta structor, a creature very similar to barbara, but of a claret-brown colour; and a minute yellow ant, the large workers of which have gigantic heads, named Pheidole (or Atta) megacephala.

My renewed observations at Mentone were carried on from October, 1871, to May, 1872, and I was able during that interval to become a frequent visitor to a warm and sheltered valley, which lay but a few minutes' walk from the house in which I lived, and in which thirty nests of the most active of the seed-storing ants were to be found.

Full therefore of my intention to resolve this difficulty if possible, I set out on October 29, 1871, immediately after my return to Mentone, to revisit this valley, where, in the previous May, I had seen the ants busily engaged in cutting, carrying, and sorting their harvest.

The spot in question was a rough slope of soft sandstone rock, with accumulations of sandy soil in the hollows, covered with a sparse and scrubby vegetation, composed of Cistus (C. salvifolius), pot-herb thyme, black lavender (Lavandula stæchas), spiny broom (Calycotome spinosa), overshadowed here and there by a few scattered stone and maritime pines, and intermixed with coarse grasses and some smaller plants.

Cultivated lemon terraces lay on the edge of the wild ground lower down in the valley, and at this season, as also in the late spring, these terraces were overgrown with a rank crop of weeds, most of which were in seed.

I had scarcely set foot on the garrigue, as this kind of wild ground is called, to distinguish it from meadows or terraced land, before I was met by a long train of ants, forming two continuous lines, hurrying in opposite directions, the one with their mouths full, the others with their mouths empty.

It was easy enough to find the nest to which these ants belonged, for it was only necessary to follow the line of ants burdened with seeds, grain, or entire capsules, which had their heads turned homewards, and there, sure enough, at about ten yards distance, and partly shaded by some small Cistus bushes, lay the nest, to and from the entrances of which the incessant stream of incomers and outgoers kept flowing.

The proceedings of the ants were the same as those previously observed in the late spring (April and May), the workers usually seeking their harvest at some distance from the nest, and going in search of it as far as the cultivated ground, where the crops of weeds were more abundant and more varied.

In a few cases, however, where the terraces were too far distant, they contented themselves with plundering the grasses, pea-flowers, honeywort, and the other denizens of the garrigue. In one case I was able to follow the thread-like column of workers from the nest to the weedy terrace where the plants grew from which they were gathering the seeds, and found that the nearly continuous double line measured twenty-four yards. Even this gives but an inadequate idea of the number of ants actively employed in the service of this colony, for hundreds of them were dispersed among the weeds on the terrace, and many were also employed in sorting the materials and in attending to the internal economy of the nest. Still this affords some evidence of the systematic and extensive scale on which foraging is carried on by this ant, and of the high importance which these creatures attach to their provision of grain.

It is not a little surprising to see that the ants bring in not only seeds of large size and fallen grain, but also green capsules, the torn stalks of which show that they have been freshly gathered from the plant. The manner in which they accomplish this feat is as follows. An ant ascends the stem of a fruiting plant, of Shepherd's-purse (Capsella Bursa pastoris) let us say, and selects a well-filled but green pod about midway up the stem, those below being ready to shed their seeds at a touch. Then, seizing it in its jaws, and fixing its hind legs firmly as a pivot, it contrives to turn round and round, and so strain the fibres of the fruit-stalk that at length they snap. It then descends the stem, patiently backing and turning upwards again as often as the clumsy and disproportionate burden becomes wedged between the thickly set stalks, and joins the line of its companions on their way to the nest. In this manner capsules of chickweed (Alsine media) and entire calyces, containing the nutlets of Calaminth, are gathered; two ants also sometimes combine their efforts, when one stations itself near the base of the peduncle and gnaws it at the point of greatest tension, while the other hauls upon and twists it. I have never seen a capsule severed from its stalk by cutting alone, and the mandibles of this ant are perhaps incompetent to perform such a task. I have occasionally seen ants engaged in cutting the capsules of certain plants drop them and allow their companions below to carry them away; and this corresponds with the curious account given by Ælian[25] of the manner in which the spikelets of corn are severed and thrown down "to the people below," τω δἡμω κἁτω..