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larvæ of their own species, and twenty pupa belonging to the negroes (F. fusca), in a glass box, the bottom of which was covered with a thick layer of earth. I placed a little honey in their corner of the prison and cut off all association with their assailants. At first they appeared to pay some little attention to the larvæ; they carried them here and there, but presently replaced them. More than one half of the Amazons (Polyerges rufescens) died of hunger in less than two days. They had not even traced out a dwelling, and the few ants in existence were languid and without strength. I commiserated their condition and gave them one of their black companions. This individual, unassisted, established order, formed a chamber in the earth, gathered together the larvæ, extricated several young ants that were ready to quit the condition of pupæ, and preserved the life of the remaining Amazons.'

The military expeditions for the purpose of capturing slaves of Polyerges rufescens have been well described by Huber and Ebrard, if we except a few errors which Forel has corrected. About the middle of the summer on fine days, from two to five hours after noon, is the best time of witnessing an expedition. At first, there is a continual running to and fro on the top of the nest; then, on a given signal, which they give by striking themselves mutually on the forehead, they start off, not all the inhabitants of the ant-hill, however, for a number always remain at home, but only a part of the militia of the state; the forces vary from a hundred to two thousand soldiers; they march in close ranks; those in front of the column wheel about, and turning back strike the foreheads of all those they meet, till they find themselves at the rear of the army; they in turn are followed by those who now march in front, thus the first become last, the first ranks being continually renewed. What can be the meaning of these repeated signals and interchange of movements? Is it that the ants in the first ranks wish to assure themselves that they are followed by the rest; and are these tappings on the forehead intended as mutual encouragements? Notwithstanding the delay caused by these undulatory movements, the march of the army is very rapid, especially in warm weather on level ground where there is no grass, leaves, or other obstacles. Now they halt for rest or consultation, now they form small detachments for exploration; then again form themselves into marching order; when they meet with an ant-hill of the F. fusca, they throw themselves upon it, invade the gates and enter the galleries, pillage the nest, running off each one with a cocoon in its mouth, and return home. If the spoil of the conquered city is abundant, they place the cocoons at the entrance of their own galleries in small packets, and return for further pillage.

The besieged ants seldom show much fight, and little blood is shed; for the invading host is composed of stout and fierce soldiers, and their military organisation is complete, while those attacked are small and undisciplined. Sometimes these last will pursue the rear-guard of their enemies, in hopes of recovering a few cocoons, but they seldom succeed; the pillagers do not take the trouble to kill them; they appear to add insult to injury, for they show their teeth, and the others, knowing what that means, run away home.

This interesting slave-making ant is not found in England; we have, however, a British species, the Formica sanguinea, which plunders the nests of other ants, carrying off their cocoons and making slaves of the developed nymphæ. It is said to be plentiful in some localities, but is certainly not common. The worker major is three or four lines in length, with a blood-red head and thorax, and a black abdomen; the worker minor is more fuscous than red; this ant makes its galleries in banks; the large workers or soldiers are a bold and a furious race; they capture the cocoons of F. fusca, F. cunicularia, and F. flava. It was Huber who first showed that sanguinea was a slave-making ant, and his account has been verified by other observers; amongst them, our own illustrious Darwin.

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Although fully trusting,' Mr. Darwin says, to the statements of Huber and Mr. Smith, I tried to approach the subject in a sceptical frame of mind, as anyone may well be 'excused for doubting the truth of so extraordinary and odious an instinct as making slaves.' But these slaves, it appears, are not submitted to any cruel bondage. Mr. Darwin examined fourteen nests and found a few slaves of F. fusca, 'the negroes' as Huber calls them, for they are black and not more than half the size of their red masters; it is only the workers of F. fusca that are found in the nests of sanguinea, the males and females occurring in their own ant-hills. But how do we know that the slaves are happy and contented in confinement? They will come out of the nest if it has been disturbed, and in common with their masters, fight in defence of their community, and will seize and carry away the exposed larvæ and nymphæ. These nests have been watched by Mr. F. Smith at various times in the months of May, June, and August, both in Surrey and Hampshire, and the slaves though present

*We have employed the usual expression of 'slave-making' ants; perhaps kidnapping' is a more appropriate term; it is the baby-and in many cases cradle as well-that is stolen.

in large numbers were never seen by him to enter or leave the nest. Hence they are strictly household slaves. Mr. Darwin, however, tells us that he once noticed a few slaves mingled with their masters leaving their nest and marching to a tall Scotch fir-tree twenty-five yards distant, probably in search of aphides or cocci. In Switzerland, the negro-slaves do not confine their attention to household duties to the same extent as in this country; there the principal part of their labour consists in searching for aphides, in closing the doors of their galleries in the evening, and opening them in the morning; for in these species, particular care is taken to close every evening all the avenues, by blocking them up with whatever ' materials they find proper for the purpose.'

M. Forel, speaking of F. fusca, tells us it is a timid species and the one that is most frequently made to work as a slave. We have already seen that when invaded by Polyerges rufescens, this little ant was easily subdued. In their battles with F. sanguinea, however, Mr. Darwin tells us they sometimes get the best of it.

'One day I fortunately witnessed a migration of F. sanguinea from one nest to another, and it was a most interesting spectacle to behold the masters carefully carrying (instead of being carried by, as in the case of F. rufescens), their slaves in their jaws. Another day of attention I was struck by about a score of the slave-makers haunting the same spot, and evidently not in search of food; they approached and were vigorously repulsed by an independent community of the slave species (F. fusca); sometimes as many as three of these ants clinging to the legs of the slave-making F. sanguinea. The latter ruthlessly killed their small opponents, and carried their dead bodies as food to their nest, twenty-nine yards distant; but they were prevented from getting any pupa to rear as slaves. I then dug up a small parcel of the pupe of F. fusca from another nest, and put them down on a bare spot near the place of combat; they were eagerly seized and carried off by the tyrants, who perhaps fancied that after all they had been victorious in the late combat.' (Origin of Species, p. 221, 1st ed.)

There is a small but courageous little yellow ant (F. flava), which is occasionally made into a slave. Mr. Darwin placed some cocoons of this species with the slave-making F. sanguinea, curious to see whether they could distinguish them from those of F. fusca; they were able to distinguish between them, for when they came across the cocoons of the little savage yellow ant, they were much terrified' and ran away; but in about a quarter of an hour, shortly after all the little ' yellow ants had crawled away, they took heart and carried off the pupa.' Mr. Darwin contrasts the instinctive habits of

F. sanguinea with those of the continental Polyerges rufescens. The differences are very remarkable; the latter can neither build, migrate, collect food for its young ones. nor even feed itself; hence it is absolutely dependent upon its slaves for everything; without slaves, that species must become extinct. Formica sanguinea gives the orders to its slaves, determines when and where a new nest shall be made, and when they migrate the masters carry the slaves; in Switzerland the slaves collect aphides for their masters and go out with them; in this country, the slaves of this latter species generally remain within their masters' house, and the masters get less work out of their slaves than they do in Switzerland.

By what steps the instinct of F. sanguinea originated I will not pretend to conjecture. But as ants, which are not slave-makers, will, as I have seen, carry of pupa of other species, if scattered near their nests, it is possible that such pupa originally stored as food might become developed, and the foreign ants thus unintentionally reared would then follow their proper instincts and do what work they could. If their presence proved useful to the species which had seized them— if it were more advantageous to the species to capture workers than to procreate them--the habit of collecting pupa originally for food might by natural selection be strengthened and rendered permanent for the very different purpose of raising slaves. When the instinct was once acquired, if carried out to a much less extent even than in our British F. sanguinea, which is less aided by its slaves than the same species in Switzerland, I can see no difficulty in natural selection increasing and modifying the instinct-always supposing each modification to be of use to the species-until an ant was formed as abjectly dependent on its slaves as is the Formica (Polyerges), rufescens.' (Origin of Species, p. 223.)

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The relation of ants with the plant-lice or aphides and the gall-flies is one of the most curious points in the history of the ant; and here again it is Huber who first gave us the best and fullest information on this subject; he showed that the aphides are the domestic milking cows of the ants, and that they are kept by them for this purpose. The aphides fix themselves upon the leaves and small branches, and insinuate their trunk or sucker between the fibres of the bark, where they find the most substantial nourishment. A portion of this aliment shortly after being taken, is expelled, under the form of small limpid drops, either by the natural passage or by two horns that we commonly observe in the posterior part of the body. This fluid constitutes the principal support of the ants. . They wait the moment the aphides eject this precious manna, pon which the ants immediately seize; but this is the least of eir talents, for they know how to obtain it at any time

'they wish.' (P. 210.) M. Forel has satisfied himself by direct observation that this sweet fluid proceeds from the natural passage, and not from the two well-known horn-like projections at the lower extremity of the aphis; these latter also secrete a substance, less fluid, however, than the sweet liquid drops. When unattended by ants the aphides by a certain jerk of the body throw out this fluid to a distance, but when ants are present, watching the moment of emission, they suck it quickly down. But ants possess the power of making the aphides yield their sweet drops at their pleasure. Huber shall tell us in his own words how the ant thus milks its cow.

He saw

an ant at first pass some aphides without stopping or disturbing them.

'It shortly after stationed itself near one of the smallest and appeared to caress it, by touching the extremity of the body alternately with its antennæ, with an extremely rapid movement. I saw with much surprise the fluid proceed from the body of the aphis, and the ant take it in his mouth. Its antennæ were afterwards directed to a much larger aphis than the first, which, on being caressed after the same manner, discharged the nourishing fluid in greater quantity, which the ant immediately swallowed; it then passed to a third, which it caressed like the preceding, by giving it several gentle blows with the antennæ on the posterior extremity of the body; the liquid was ejected at the same moment, and the ant lapped it up. It then proceeded to a fourth; this, probably already exhausted, resisted its action. The ant, who in all probability knew it had nothing to hope for by remaining there, quitted it for a fifth, from whom it obtained its expected supply. It now returned perfectly contented to its nest.' (P. 213.)

It appears that this tapping with the antennæ is a constant preliminary to the emission of the fluid, and that the aphis voluntarily submits to the operation, giving greater facility for the ant's taps by lowering the head. Should the aphides remain long unmilked by the ants, they deposit their fluid upon the leaves, where the ants find it on their return; the aphides never resist the solicitation of the ants when in a state to satisfy them. This curious alliance, as Forel remarks, between the ants and the aphides consists of an exchange of good services, for the ants protect their cattle against numerous enemies, such as the larva of the ladybird beetles (Coccinella), and of some of the Diptera as the Syrphus. Some kind of ants are in the habit of transporting their cows from one place to another. The greatest cow-keeper of all, perhaps, is the yellow ant (Lasius flavus). This ant is more decidedly a stay-at-home species, and likes to have all its conveniences within reach ; it never goes far from its abode, and does not search the trees for aphides or any kind of food; it is a small yellow ant, the

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