Animal Intelligence Part 5

_Habit of making Slaves._--This habit, or instinct, obtains among at least three species of ant, viz., _Formica rufescens_, _F. sanguinea_, and _strongylognathus_. It was originally observed by P. Huber in the first-named species. Here the species enslaved is _F. fusca_, which is appropriately coloured black. The slave-making ants attack a nest of _F.

fusca_ in a body; there is a great fight with much slaughter, and, if victorious, the slave-makers carry off the pupae of the vanquished nest in order to hatch them out as slaves. Mr. Darwin gives an account of a battle which he himself observed.[29]

When the pupae hatch out in the nest of their captors, the young slaves begin their life of work, and seem to regard their master's home as their own; for they never attempt to escape, and they fight no less keenly than their masters in defence of the nest. _F. sanguinea_ content themselves with fewer slaves than do _F. rufescens_; and the work that devolves upon the slaves differs according to the species which has enslaved them. In the nests of _F. sanguinea_ the comparatively few captives are kept as household slaves; they never either enter or leave the nest, and so are never seen unless the nest is opened. They are then very conspicuous from the contrast which their black colour and small size present to the red colour and much larger size of _F. rufescens_.

As the slaves are by this species kept strictly indoors, all the outdoor work of foraging, slave-capturing, &c., is performed by the masters; and when for any reason a nest has to migrate, the masters carry their slaves in their jaws. _F. rufescens_, on the other hand, a.s.signs a much larger share of labour to the slaves, which, as we have already seen, are present in much larger numbers to take it. In this species the males and fertile females do no work of any kind; and the workers, or sterile females, though most energetic in capturing slaves, do no other kind of work. Therefore the whole community is absolutely dependent upon its slaves. The masters are not able to make their own nests or to feed their own larvae. When they migrate, it is the slaves that determine the migration, and, reversing the order of things that obtains in _F.

sanguinea_, carry their masters in their jaws. Huber shut up thirty masters without a slave and with abundance of their favourite food, and also with their own larvae and pupae as a stimulus to work; but they could not feed even themselves, and many died of hunger. He then introduced a single slave, and she at once set to work, fed the surviving masters, attended to the larvae, and made some cells.

In order to confirm this observation, Lespes placed a piece of sugar near a nest of slave-makers. It was soon found by one of the slaves, which gorged itself and returned to the nest. Other slaves then came out and did likewise. Then some of the masters came out, and, by pulling the legs of the feeding slaves, reminded them that they were neglecting their duty. The slaves then immediately began to serve their masters with the sugar. Forel also has confirmed all these observations of Huber. Indeed, in the case of _F. rufescens_, the structure of the animal is such as to render self-feeding physically impossible. Its long and narrow jaws, adapted to pierce the head of an enemy, do not admit of being used for feeding, unless liquid food is poured into them by the mouth of a slave. This fact shows of how ancient an origin the instinct of slave-making must be; it has altered in an important manner a structure which could not have been so altered prior to the establishment of the instinct in question.

Mr. Darwin thus sums up the differences in the offices of the slaves in the nests of _F. sanguinea_ and _F. rufescens_ respectively:--

The latter does not build its own nest, does not determine its own migrations, does not collect food for itself or for its fellows, and cannot even feed itself; it is absolutely dependent on its numerous slaves. _Formica sanguinea_, on the other hand, possesses much fewer slaves, and in the early part of the summer extremely few; the masters determine when and where a new nest shall be formed, and when they migrate, the masters carry the slaves. Both in Switzerland and England the slaves seem to have the exclusive care of the larvae, and the masters alone go on slave-making expeditions. In Switzerland the slaves and masters work together, making and bringing materials for the nest; both, but chiefly the slaves, tend and milk, as it may be called, their aphides; and thus both collect food for the community. In England the masters alone usually leave the nest to collect building materials and food for themselves, their slaves and larvae. So that the masters in this country receive much less service from their slaves than they do in Switzerland.

Mr. Darwin further observes that 'this difference in the usual habits of the masters and slaves in the two countries probably depends merely on the slaves being captured in greater numbers in Switzerland than in England;' and records that he has observed in a community of the English species having an unusually large stock of slaves that 'a few slaves mingled with their masters leaving the nest, and marched along the same road to a tall Scotch fir tree, twenty-five yards distant, which they ascended together, probably in search of aphides or cocci.' And, according to Huber, the princ.i.p.al office of the slaves in Switzerland is to search for aphides.

Mr. Darwin also made the following observation:--'Desiring to ascertain whether _F. sanguinea_ could distinguish the pupae of _F. fusca_, which they habitually make into slaves, and which are an unwarlike species, from _F. flava_, which they rarely capture, and never without a severe fight,' he found 'it was evident that they did at once distinguish them;' for while 'they eagerly and instantly seized the pupae of _F.

fusca_, they were much terrified when they came across the pupae, or even the earth from the nest, of _F. flava_, and quickly ran away; but in about a quarter of an hour, shortly after the little yellow ants had crawled away (from their nest having been disturbed by Mr. Darwin), they took heart and carried off the pupae.'

Concerning the origin of this remarkable instinct, Mr. Darwin writes:--

As ants which are not slave-makers will, as I have seen, carry off pupae of other species if scattered near their nests, it is possible that such pupae 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 pupae, 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, as we have seen, is less aided by its slaves than the same species in Switzerland, natural selection might increase and modify the instinct, always supposing such modification to be of use to the species, until an ant was found as abjectly dependent on its slave as is the _Formica rufescens_.

Ants do not appear to be the only animals of which ants make slaves; for there seems to be at least one case in which these wonderful insects enslave insects of another species, which therefore may be said to stand to the ants in the relation of beasts of burden. The case to which I allude is one that is recorded in Perty's 'Intellectual Life of Animals'

(2nd ed. p. 329), and is as follows:--

According to Audubon certain leaf-bugs are used as slaves by the ants in the Brazilian forests. When these ants want to bring home the leaves which they have bitten off the trees, they do it by means of a column of these bugs, which go in pairs, kept in order on either side by accompanying ants. They compel stragglers to re-enter the ranks, and laggards to keep up by biting them. After the work is done the bugs are shut up within the colony and scantily fed.

_Wars._--On the wars of ants a great deal might be said, as the facts of interest in this connection are very numerous; but for the sake of brevity I shall confine myself to giving only a somewhat meagre account.

One great cause of war is the plundering of ants' nests by the slave-making species. Observers all agree that this plundering is effected by a united march of the whole army composing a nest of the slave-making species, directed against some particular nest of the species which they enslave. According to Lespes and Forel, single scouts or small companies are first sent out from the nest to explore in various directions for a suitable nest to attack. These scouts afterwards serve as guides to the marauding excursion. Forel saw several of these scouts of the species _F. rufescens_ or Amazon carefully inspecting a nest of _F. fusca_ which they had found, investigating especially the entrances. These are purposely made difficult to find by their architects, and it not unfrequently happens that after all precautions and inspections on the part of the invaders, an expedition fails on account of not finding the city gates.

When the scouts have been successful in discovering a suitable nest to plunder, and have completed their strategical investigations of the locality to their satisfaction, they return straight to their own nest or fortress. Forel has then seen them walking about on the surface of their nest for a long time, as if in consultation, or making up their minds. Then some of them entered the nest, soon after which hosts of warriors streamed out of the entrances, and ran about tapping each other with their heads and antennae. They then formed into column and set out to pillage the nest of the slave ants. The following is the account which Lespes gives of such expeditions:--

They only take place towards the end of the summer and in autumn. At this time the winged members of the slave species (_F. fusca_ and _F. cunicularia_) have left the nest, and the Amazons will not take the trouble to bring back useless consumers. When the sky is clear our robbers leave their town in the afternoon at about three or four o'clock. At first no order is perceptible in their movements, but when they are all gathered together they form a regular column, which then moves forward quickly, and each day in a different direction. They march closely pressed together, and the foremost always appear to be seeking for something on the ground. They are each moment overtaken by others, so that the head of the column is continually growing. They are in fact seeking the traces of the ants which they propose to plunder, and it is scent that guides them. They snuff over the ground like hounds following the track of a wild animal, and when they have found it they plunge headlong forward, and the whole column rushes on behind. The smallest armies I saw consisted of several hundred individuals, but I have also seen some four times as large. They then form columns which may be five metres long, and as much as fifty centimetres wide. After a march, which often lasts a full hour, the column arrives at the nest of the slave species.

The _F. cuniculariae_, which are the strongest, offer keen opposition, but without much result. The Amazons soon penetrate within the nest, to come out again a moment later, while the a.s.sailed ants at the same time rush out in ma.s.ses. During the whole time attention is directed solely to the larvae and pupae, which the Amazons steal while the others try to save as many as possible. They know very well that the Amazons cannot climb, so they fly with their precious burdens to the surrounding bushes or plants, whereto their enemies cannot follow them. They then pursue the retreating robbers and try to take away from them as much of their booty as possible. But the latter do not trouble themselves much about them, and hasten on home. On their return they do not follow the shortest road, but exactly the one by which they came, finding their way back by smell. Arrived at their nest, they immediately hand over their booty to the slaves, and trouble themselves no more about it. A few days afterwards the stolen pupae or nymphae emerge, without memory of their childhood, and immediately and without compulsion take part in all tasks.

According to Buchner's account,[30]--

From time to time the army makes a short halt, partly to let the rearguard close up, partly because different opinions arise as to the direction of the host, or because the place at which they are is unknown to them. Forel several times saw the army completely lose its way--an incident only once observed by Huber. Forel puts the number of warriors in such an army at from one hundred to more than two thousand. Its speed is on an average a metre per minute, but varies much according to circ.u.mstances, and is naturally least when returning laden with booty. If the distance be very great, such bodily fatigue may at last be felt that the whole attack on the hostile nest is given up, and a retreat is begun; Forel once saw this happen after they had pa.s.sed over a distance of two hundred and forty yards. Sometimes it seems as though, on coming within sight of the hostile nest, a kind of discouragement took possession of them, and prevented their making the attack. If the nest cannot at once be found, the whole army halts, and some divisions are sent forward to search for it, and these are gradually seen returning towards the centre. Forel also saw such an army only searching the first day, advancing zigzag, and with frequent halts, whereas on the following day it went forward to its aim swiftly and without delay, having found out the road. It seems that a single ant, even if it knows the way and the place, is not able alone to lead a large army, but that a considerable number must be employed in this duty. Mistakes as to the road occur with special ease during the return journey, because the several ants are laden with booty and cannot readily understand each other. Individual ants are then seen to wander about in every direction often for a long time, until they at last reach a spot known to them, and then advance swiftly to their goal. Many never come back at all. These mistakes easily occur when the robbers which have pa.s.sed into a hostile nest do not come out again at the same holes whereby they entered, but by others at some distance--for instance, by a subterranean ca.n.a.l. Coming out thus in a strange neighbourhood, they do not know which way to take, and only some chance to find the right road during their aimless wanderings about, and recognise and follow it by smell. On the other hand, such mistakes scarcely ever happen to individuals in an unladen train, kept in good array. Other species of ants (_F. fusca_, _rufa_, _sanguinea_) know better how to manage under such circ.u.mstances than do the Amazons. The laden ones lay down their loads, first find where they are, and only take them up again after they have found their way. If the booty seized in the nest first attacked is too large to be all taken at once, the robbers return once, or oftener, so as to complete their work... .

The ants, as already said, have no regular leaders nor chiefs, yet it is certain that in each expedition, alteration of road, or other change, the decision during that event comes from a small knot of individuals, which have previously come to an understanding, and carry the rest and the undecided along with them. These do not always follow immediately, but only after they have received several taps on the head from the members of the 'ring.' The procession does not advance until the leaders have convinced themselves by their own eyesight that the main part of the army is following.

One day Forel saw some Amazons on the surface of a nest of the _F. fusca_ seeking and sounding in all directions, without being able to find the entrance.

At last one of them found a very little hole, hardly as large as a pin's head, through which the robbers penetrated. But since, owing to the smallness of the hole, the invasion went on slowly, the search was continued, and an entrance was found further off, through which the Amazon army gradually disappeared.

All was quiet. About five minutes later Forel saw a booty-laden column emerge from each hole. Not a single ant was without a load. The two columns united outside and retreated together.

A marauding excursion of the Amazons against the _F.

rufibarbis_, a sub-species of the _F. fusca_, or small black ants, took place as follows:--The vanguard of the robber army found that it had reached the neighbourhood of the hostile nest more quickly than it had expected; for it halted suddenly and decidedly, and sent a number of messengers which brought up the main body and the rearguard with incredible speed. In less than thirty seconds the whole army had closed up, and hurled itself in a ma.s.s on the dome of the hostile nest. This was the more necessary as the _rufibarbes_ during the short halt had discovered the approach of the enemy, and had utilised the time to cover the dome with defenders. An indescribable struggle followed, but the superior numbers of the Amazons overcame, and they penetrated into the nest, while the defenders poured by thousands out of the same holes, with their larvae and pupae in their jaws, and escaped to the nearest plants and bushes, running over the heaps of their a.s.sailants. These looked on the matter as hopeless, and began to retreat. But the _rufibarbes_, furious at their proceedings, pursued them, and endeavoured to get away from them the few pupae they had obtained, by trying to seize the Amazons' legs and to s.n.a.t.c.h away the pupae. The Amazon lets its jaws slip slowly along the captive pupa, as far as the head of its opponent, and pierces it, if it does not, as generally happens, draw back. But it often manages to seize the pupa at the instant at which the Amazon lets it go and flies with it. This is managed yet more easily when a comrade holds the robber by the legs, and compels it to loose its prey in order to guard itself against its a.s.sailant. Sometimes the robbers seize empty coc.o.o.ns and carry them away, but they leave them on the road when they have discovered their mistake. In the above case the strength of the _rufibarbes_ proved at last so great that the rearguard of the retreating army was seriously pressed, and was obliged to give up its booty. A number of the Amazons also were overpowered and killed, but not without the _rufibarbes_ also losing many people. None the less did some individuals, as though desperate, rush into the thickest hosts of the enemy, penetrated again into the nest, and carried off several pupae by sheer audacity and skill. Most of them left their prey to go to the help of their comrades when a.s.sailed by the _rufibarbes_. Ten minutes after the commencement of the retreat all the Amazons had left the nest, and, being swifter than their opponents, they were only pursued for about halfway back. Their attack had failed on account of a short delay!

On another occasion observed by Forel, in which several fertile Amazons also took part and killed many enemies, the nest was thoroughly ravished, but the retreat was also in this case very much disturbed and hara.s.sed by the superior numbers of the enemy. There were many slain on both sides. That in spite of the above-mentioned unanimity different opinions among the members of an expedition sometimes hinder its conduct, the following observation seems to show:--An advancing column divided after it had gone about ten yards from the nest. Half turned back, while the other half went on, but after some time hesitated and also turned back. Arrived at home, it found those which had formerly turned back putting themselves in motion in a new direction. The newly returned followed them, and the reunited army, after various wheelings, halts, &c., at last turned home again by a long way round.

The whole business looked like a promenade. But apparently different parties had different nests in view, while others were entirely against the expedition. Yet perhaps it was only a march for exercise.

Outer obstacles do not, as a rule, hinder the Amazons when they are once on the march. Forel saw them wade through some shallow water, although many were drowned in it, and then march over a dusty high road, although the wind blew half of them away. As they returned, booty-laden, neither wind, nor dust, nor water could make them lay down their prey. They only got back with great trouble, and turned back again to bring fresh booty, although many lost their lives.

The following is also quoted from Buchner's excellent epitome of Forel's observations in this connection:--

The most terrible enemy of the Amazons is the sanguine ant (_F. sanguinea_), which also keeps slaves, and thereby often comes into collision with the Amazons on their marauding excursions. It is not equal to it in bodily strength or fighting capacity, but surpa.s.ses it in intelligence; according to Forel it is the most intelligent of all the species of ants. If Forel, for instance, poured out the contents of a sack filled with a nest of the slave species near an Amazon nest, the Amazons apparently generally regarded the tumbled together heap of ants, larvae, pupae, earth, building materials, &c., as the dome of a hostile nest, and took all imaginable but useless pains to find out the entrances thereinto, leaving on one side for this investigation their only object, the carrying off the pupae; but the sanguine ants under similar circ.u.mstances did not allow themselves to be deceived, but at once ransacked the whole heap.

On another occasion, while a procession of Amazon ants was on its way to plunder a nest of _F. fusca_, before it arrived Forel poured out a sack-full of sanguine ants, and made a break in the nest:--

The sanguine ants pressed in, while the _fusca_ came out to defend themselves. At this moment the first Amazons arrived. When they saw the sanguine ants they drew back and awaited the main army, which appeared much disturbed at the news. But once united, the bold robbers rushed at their foes. The latter gathered together and beat back the first attack, but the Amazons closed up their ranks and made a second a.s.sault, which carried them on to the dome and into the midst of the enemy. These were overthrown, as well as a number of _F. pratensis_, which Forel at this moment poured out on the nest. The conquerors delayed for a moment on the dome after their victory, and then entered the nest to bring out a little of the valuable booty. A few Amazons which were mad with anger did not return with the main army, but went on slaughtering blindly among the conquered and the fugitives of the three species, _fusca_, _pratensis_, and _sanguinea_.

The ravished _rufibarbes_ once became so desperate at their overthrow that they followed the robbers to their own nest, and the latter had some trouble in defending it. The _rufibarbes_ let themselves be killed in hundreds, and really seemed as though they courted death. A small number of the Amazons also sank under the bites of their enemies. The nest contained slaves of the _rufibarbis_ species, which on this emergency fought actively against their own race.

There were also slaves of the species _fusca_, so that the nest included three different species of ants.

The same nest is often revisited many times on the same day or at different periods, until either there is no more to steal, or the plundered folk have hit upon better mode of defence. A column which was in the act of going back to such a plundered nest turned when halfway there, and halted, apparently on no other ground than because it had met the rearguard of the army, and had learned that the nest was exhausted, and that there was nothing more to be had there. The robbers then went off to a _rufibarbis_ nest which was in the neighbourhood, and killed half the inhabitants while plundering the nest. The surviving _rufibarbes_ returned after the robbery and brought up new progeny; but thirteen days later the Amazons again reaped a rich harvest from the same nest. The Amazon army often severs itself into two separate divisions when there is not enough for both to do at the same spot.

Sometimes one division finds something and the other nothing, and they then reunite. If any obstacle be placed in their way they try to overcome it, in doing which some leave the main army, lose themselves, and only find their way home again with difficulty. Forel has tried to establish the normal frequency of expeditions, and found that a colony watched by himself for a s.p.a.ce of thirty days sent out no less than forty-four marauding excursions. Of these about eight-and-twenty were completely, nine partially, and the remainder not at all successful. He four times saw the army divide into two. Half the expeditions were levelled against the _rufibarbes_, half against the _fuscae_. On an average a successful expedition would bring back to the colony a thousand pupae or larvae. On the whole, the number of future slaves stolen by a strong colony during a favourable summer may be reckoned at forty thousand!

The internecine battles which occasionally break out among the Amazons themselves are naturally the most cruel. They tear each other to pieces with incredible fury, and knots of five or six individuals which have pierced each other may be seen rolling over each other on the ground, it being impossible to distinguish between friend and foe. Civil wars among men are also known to be the most embittered and the most b.l.o.o.d.y.

The mode of attack practised by the other best known species of slave-making ant, _sanguinea_, is somewhat different:--

They march in small troops which, in case of need, summon reinforcements, and therefore as a rule only reach their goal slowly. Between the individual troops messengers or scouts run continually backwards and forwards. The first troop which arrives at the hostile nest does not rush at it, as do the Amazons, but contents itself with making provisional reconnaissances, wherein some of the a.s.sailants are generally made prisoners by the enemy, which have time to bethink and to collect themselves. Reinforcements are now brought up, and a regular siege of the nest begins. A sudden invasion, like that of the Amazons, is never seen. The besieging army forms a complete ring round the hostile nest, and the besiegers hold this with mandibles open and antennae drawn back, without going nearer. In this position they beat off all a.s.saults of the besieged, until they feel themselves strong enough to advance to the attack.

This attack scarcely ever fails, and has for its chief object the mastering of the entrances and outlets of the nest. A special troop guards each opening, and only allows such of the besieged to pa.s.s out as carry no pupae. This manoeuvre gives rise to a number of comical and characteristic scenes. By this means the sanguine ants in a few minutes manage to have all the defenders out of the nests and the pupae left behind.

This is the case at least with the _rufibarbes_, while the rather less timid _fuscae_ try, even at the last moment when it is useless, to stop up or barricade the entrances. The sanguine ants do not indeed possess the terrible weapons and the warlike impetuosity of the Amazons, but they are stronger and larger. If a _fusca_ or a _rufibarbis_ fights with a sanguine ant for the possession of a pupa, it is generally very soon overcome. While the main part of the army is penetrating into the nest to steal the pupae, some divisions pursue the fugitives, to take away from them the few pupae which may chance to have been saved. They drive them even out of the cricket-holes in which they have meanwhile taken refuge. In short, it is a _razzia_, or sweeping burglary, as complete as can be imagined. In the retreat the robbers in no wise hurry themselves, for they know that they are threatened by no danger and no loss, and the complete emptying of a large and distant nest often takes several days in accomplis.h.i.+ng. The ants which have been so thoroughly robbed scarcely ever return to their former abode.

It must be admitted that a human army, robbing a foreign town or fortress, could not behave better or more prudently.

Huber gives the following account of a battle waged by sanguine ants:--

At ten, in a July morning, he noticed a small band of them emerge from their nest, and march rapidly towards a nest of negroes, around which it dispersed. A number of the blacks rushed out, gave battle, and succeeded in defeating their invaders, and in making several of them prisoners. Upon this, the remainder of the attacking force waited for a reinforcement. When this came up, they still declined further proceedings, and sent more aides-de-camp to their own nest. The result of these messages was a much larger reinforcement; but even yet the pirates appeared to shun the combat. At last, the negroes marched out from their nest in a phalanx of about two feet square, and a number of skirmishes began, which soon ended in a general _melee_. Long before the event seemed certain, the negroes carried off their pupae to the most distant part of the nest; and when, after a longer encounter, they appeared to think further resistance vain, they retreated, attempting to take with them their young.

In this, however, they were prevented, and the invaders obtained possession of their nest and the booty. When they had done this, they put in a garrison, and occupied the night and the succeeding day in carrying off their spoil.

Buchner says--

Battles between ants of the same species often end with a lasting alliance, especially when the number of the workers on both sides is comparatively small. The wise little animals under such circ.u.mstances discover, much more quickly and better than men, that they can only destroy each other by fighting, while union would benefit both parties. Sometimes they drive each other out of their nests in a quite friendly way. Forel laid on a table a piece of bark with a nest of the gentle _Leptothorax acervorum_, and then put on it the contents of another nest of the same species. The last comers were by far the more numerous, and soon possessed themselves of the nest, driving out the inmates. But the latter did not know whither to go, and turned back again. They were then seized by their opponents one after the other, carried away as far as possible from the nest, and there put down. The oftener they came back the further were they carried away. One of the carriers arrived in this fas.h.i.+on at the edge of the table, and after it had by means of its feelers convinced itself that it had reached the end of the world, mercilessly let its burden drop into the fathomless abyss. It waited a moment to see if it had attained its object, and then turned back to the nest. Forel picked up the ant which had fallen on the floor, and put it down right in front of the returning ant. The latter repeated the same manoeuvre as at first, only stretching its neck further over the edge of the table. He several times reiterated his experiment, and always with the same result. Later the two colonies were shut up together in a gla.s.s case, and gradually learned to agree.

At other times, however, warlike ants show great and needless cruelty to one another:--

They slowly pull from their victim, that is rendered defenceless by wounds, exhaustion, or terror, first one feeler and then the other, then the legs one after another, until they at last kill it, or pull it in a completely mutilated and helpless condition to some out-of-the-way spot where it perishes miserably. Yet some compa.s.sionate hearts are to be found among the victors, which only pull the conquered to a distant place in order to get rid of them, and there let them go without injuring them.

The following account is also taken from Buchner's 'Mind in Animals,' p.

87:--

The doors are often guarded by special sentries, which fulfil their important duty in various ways. Forel saw a nest of the _Colobopsis truncata_, the two or three very small round openings of which were watched by soldiers, arranged so that their thick cylindrical heads stopped them up, just as a cork stops up the mouth of a bottle. The same observer saw the _Myrmecina Latreillei_ defend themselves against the invasions of the slave-making _Strongylognathus_, by placing a worker at each of the little openings of the nest, which quite stops up the opening either with its head or abdomen. The _Camponotus_ species also defend their nests by stretching their heads in front of the openings, drawing back the antennae. Each approaching enemy thus receives a sharp blow or bite delivered with the whole weight of the body. MacCook noticed in the nests of the soon to be described Pennsylvanian mound-building ants, the employment of special sentries, which lay watching within the nest entrances, and sprang out at the first sight of danger to attack the enemy; and it was wonderful to see with what swiftness the news of such an alarm spread through the nest, and how the inhabitants came out _en ma.s.se_ to meet the enemy. The _Lasius_ species defend their large, strong, and very extensive nests against hostile attack or sieges with equal courage and skill, while other timid species seek to fly as speedily as possible with their larvae, pupae, and fruitful queens.

There is, as Forel tells us, a regular barricade fight. Pa.s.sage after pa.s.sage is stopped and defended to the uttermost, so that the a.s.sailants can only advance step and step. Unless the latter are in an enormous majority, the struggle may last a very long time with these tactics. During this time, other workers are busy preparing subterranean pa.s.sages backwards for eventual flight. Generally such pa.s.sages are already made, and during a fight a new dome of the _Lasius_ may be seen rising at a distance, it not being difficult for them to make this with the help of their extended subterranean pa.s.sages and communications.

The _F. exsecta_ or _pressilabris_ fights in a peculiar way, which is due to care of their small and very tender bodies. It avoids all single combats, and always fights in closed ranks. Only when it thinks victory secure does it spring on its enemy's back. But its chief strength lies in the fact that many together always attack a foe. They nail down their opponent by seizing its legs and holding them firmly to the ground, while a comrade springs on the back of the defenceless creature and tries to bite through its neck. But if threatened the holders sometimes take flight, and so it happens that in battles between the _exsectae_ and the much stronger _pratenses_ not a few of the latter are seen running about with a small enemy clutching their shoulders, and making violent efforts to tear the neck of its foe. If the bearer is then seized with cramp, the nervous cord has been injured. On the other hand, if an _exsecta_ is seized by the back by a _pratensis_ it is at once lost.

The tactics of the turf ants resemble those of the _exsectae_, three or four of them seizing an opponent and pulling off his legs. In similar fas.h.i.+on the attack of the _Lasius_ species is chiefly directed against the legs of its enemies, three, four, or five uniting in the effort. They understand barricade fighting particularly well in their large well-built dwellings, and if it comes to the worst fly by subterranean pa.s.sages. They are feared by most ants on account of their numerical superiority. Forel one day poured the contents of ten nests of _pratenses_ in front of a tree trunk inhabited by _Lasius fuliginosus_ (jet ant). The siege at once began; but the jet ants called in help from the nests connected with their colony, and thick black columns were at once seen coming out from the surrounding trees. The _pratenses_ were obliged to fly, and left behind them a ma.s.s of dead as well as their pupae, which last were carried off by the victors to their nests to be eaten.