Chapter VI. The Red Ants
Jean-Henri Fabre Mason-bees
Red Imported Fire Ant (Solenopsis invicta)
The Pigeon transported for hundreds of miles is able to find his way back to his Dove-cot; the Swallow, returning from his winter quarters in Africa, crosses the sea and once more takes possession of the old nest. What guides them on these long journeys? Is it sight? An observer of supreme intelligence, one who, though surpassed by others in the knowledge of the stuffed animal under a glass case, is almost unrivalled in his knowledge of the live animal in its wild state, Toussenel (1), the admirable writer of „L'Esprit des betes“, speaks of sight and meteorology as the Carrier-pigeon's guides:
‚The French bird,‘ he says, ‚knows by experience that the cold weather comes from the north, the hot from the south, the dry from the east and the wet from the west. That is enough meteorological knowledge to tell him the cardinal points and to direct his flight. The Pigeon taken in a closed basket from Brussels to Toulouse has certainly no means of reading the map of the route with his eyes; but no one can prevent him from feeling, by the warmth of the atmosphere, that he is pursuing the road to the south. When restored to liberty at Toulouse, he already knows that the direction which he must follow to regain his Dove-cot is the direction of the north. Therefore he wings straight in that direction and does not stop until he nears those latitudes where the mean temperature is that of the zone which he inhabits. If he does not find his home at the first onset, it is because he has borne a little too much to the right or to the left. In any case, it takes him but a few hours‘ search in an easterly or westerly direction to correct his mistake.'
The explanation is a tempting one when the journey is taken north and south; but it does not apply to a journey east and west, on the same isothermal line. Besides, it has this defect, that it does not admit of generalization. One cannot talk of sight and still less of the influence of a change of climate when a Cat returns home, from one end of a town to the other, threading his way through a labyrinth of streets and alleys which he sees for the first time. Nor is it sight that guides my Mason-bees, especially when they are let loose in the thick of a wood. Their low flight, eight or nine feet above the ground, does not allow them to take a panoramic view nor to gather the lie of the land. What need have they of topography? Their hesitation is short-lived: after describing a few narrow circles around the experimenter, they start in the direction of the nest, despite the cover of the forest, despite the screen of a tall chain of hills which they cross by mounting the slope at no great height from the ground. Sight enables them to avoid obstacles, without giving them a general idea of their road. Nor has meteorology aught to do with the case: the climate has not varied in those few miles of transit. My Mason-bees have not learnt from any experience of heat, cold, dryness and damp: an existence of a few weeks' duration does not allow of this. And, even if they knew all about the four cardinal points, there is no difference in climate between the spot where their nest lies and the spot at which they are released; so that does not help them to settle the direction in which they are to travel.
To explain these many mysteries, we are driven therefore to appeal to yet another mystery, that is to say, a special sense denied to mankind. Charles Darwin, whose weighty authority no one will gainsay, arrives at the same conclusion. To ask if the animal be not impressed by the terrestrial currents, to enquire if it be not influenced by the close proximity of a magnetic needle: what is this but the recognition of a magnetic sense? Do we possess a similar faculty? I am speaking, of course, of the magnetism of the physicists and not of the magnetism of the Mesmers and Cagliostros. Assuredly we possess nothing remotely like it. What need would the mariner have of a compass, were he himself a compass?
And this is what the great scientist acknowledges: a special sense, so foreign to our organism that we are not able to form a conception of it, guides the Pigeon, the Swallow, the Cat, the Mason-bee and a host of others when away from home. Whether this sense be magnetic or no I will not take upon myself to decide; I am content to have helped, in no small degree, to establish its existence. A new sense added to our number: what an acquisition, what a source of progress! Why are we deprived of it? It would have been a fine weapon and of great service in the struggle for life. If, as is contended, the whole of the animal kingdom, including man, is derived from a single mould, the original cell, and becomes self-evolved in the course of time, favouring the best-endowed and leaving the less well-endowed to perish, how comes it that this wonderful sense is the portion of a humble few and that it has left no trace in man, the culminating achievement of the zoological progression? Our precursors were very ill-advised to let so magnificent an inheritance go: it was better worth keeping than a vertebra of the coccyx or a hair of the moustache.
Does not the fact that this sense has not been handed down to us point to a flaw in the pedigree? I submit the little problem to the evolutionists; and I should much like to know what their protoplasm and their nucleus have to say to it.
Is this unknown sense localized in a particular part of the Wasp and the Bee? Is it exercised by means of a special organ? We immediately think of the antennae. The antennae are what we always fall back upon when the insect's actions are not quite clear to us; we gladly put down to them whatever is most necessary to our arguments. For that matter, I had plenty of fairly good reasons for suspecting them of containing the sense of direction. When the Hairy Ammophila (2) is searching for the Grey Worm, it is with her antennae, those tiny fingers continually fumbling at the soil, that she seems to recognize the presence of the underground prey. Could not those inquisitive filaments, which seem to guide the insect when hunting, also guide it when travelling? This remained to be seen; and I did see.
I took some Mason-bees and amputated their antennae with the scissors, as closely as I could. These maimed ones were then carried to a distance and released. They returned to the nest with as little difficulty as the others. I once experimented in the same way with the largest of our Cerceres (Cerceris tuberculata) (3); and the Weevil-huntress returned to her galleries. This rids us of one hypothesis: the sense of direction is not exercised by the antennae. Then where is its seat? I do not know.
What I do know is that the Mason-bees without antennae, though they go back to the cells, do not resume work. They persist in flying in front of their masonry, they alight on the clay cup, they perch on the rim of the cell and there, seemingly pensive and forlorn, stand for a long time contemplating the work which will never be finished; they go off, they come back, they drive away any importunate neighbour, but they fetch and carry no more honey or mortar. The next day, they do not appear. Deprived of her tools, the worker loses all heart in her task. When the Mason-bee is building, the antennae are constantly feeling, fumbling and exploring, superintending, as it were, the finishing touches given to the work. They are her instruments of precision; they represent the builder's compasses, square, level and plumb-line.
Hitherto my experiments have been confined to the females, who are much more faithful to the nest by virtue of their maternal responsibilities. What would the males do if they were taken from home? I have no great confidence in these swains who, for a few days, form a tumultuous throng outside the nests, wait for the females to emerge, quarrel for their possession, amid endless brawls, and then disappear when the works are in full swing. What care they, I ask myself, about returning to the natal nest rather than settling elsewhere, provided that they find some recipient for their amatory declarations? I was mistaken: the males do return to the nest. It is true that, in view of their lack of strength, I did not subject them to a long journey: about half a mile or so. Nevertheless, this represented to them a distant expedition, an unknown country; for I do not see them go on long excursions. By day, they visit the nests or the flowers in the garden; at night, they take refuge in the old galleries or in the interstices of the stone-heaps in the harmas.
The same nests are frequented by two Osmia-bees (Osmia tricornis and Osmia Latreillii), who build their cells in the galleries left at their disposal by the Chalicodomae. The most numerous is the first, the Three-horned Osmia. It was a splendid opportunity to try and discover to what extent the sense of direction may be regarded as general in the Bees and Wasps; and I took advantage of it. Well, the Osmiae (Osmia tricornis), both male and female, can find their way back to the nest. My experiments were made very quickly, with small numbers and over short distances; but the results agreed so closely with the others that I was convinced. All told, the return to the nest, including my earlier attempts, was verified in the case of four species: the Chalicodoma of the Sheds, the Chalicodoma of the Walls, the Three-horned Osmia and the Great or Warted Cerceris (Cerceris tuberculata) (4). Shall I generalize without reserve and allow all the Hymenoptera (5) this faculty of finding their way in unknown country? I shall do nothing of the kind; for here, to my knowledge, is a contradictory and very significant result.
Among the treasures of my harmas-laboratory, I place in the first rank an Ant-hill of Polyergus rufescens, the celebrated Red Ant, the slave-hunting Amazon. Unable to rear her family, incapable of seeking her food, of taking it even when it is within her reach, she needs servants who feed her and undertake the duties of housekeeping. The Red Ants make a practice of stealing children to wait on the community. They ransack the neighbouring Ant-hills, the home of a different species; they carry away nymphs, which soon attain maturity in the strange house and become willing and industrious servants.
When the hot weather of June and July sets in, I often see the Amazons leave their barracks of an afternoon and start on an expedition. The column measures five or six yards in length. If nothing worthy of attention be met upon the road, the ranks are fairly well maintained; but, at the first suspicion of an Ant-hill, the vanguard halts and deploys in a swarming throng, which is increased by the others as they come up hurriedly. Scouts are sent out; the Amazons recognize that they are on a wrong track; and the column forms again. It resumes its march, crosses the garden-paths, disappears from sight in the grass, reappears farther on, threads its way through the heaps of dead leaves, comes out again and continues its search. At last, a nest of Black Ants is discovered. The Red Ants hasten down to the dormitories where the nymphs lie and soon emerge with their booty. Then we have, at the gates of the underground city, a bewildering scrimmage between the defending blacks and the attacking reds. The struggle is too unequal to remain indecisive. Victory falls to the reds, who race back to their abode, each with her prize, a swaddled nymph, dangling from her mandibles. The reader who is not acquainted with these slave-raiding habits would be greatly interested in the story of the Amazons. I relinquish it, with much regret: it would take us too far from our subject, namely, the return to the nest.
The distance covered by the nymph-stealing column varies: it all depends on whether Black Ants are plentiful in the neighbourhood. At times, ten or twenty yards suffice; at others, it requires fifty, a hundred or more. I once saw the expedition go beyond the garden. The Amazons scaled the surrounding wall, which was thirteen feet high at that point, climbed over it and went on a little farther, into a cornfield. As for the route taken, this is a matter of indifference to the marching column. Bare ground, thick grass, a heap of dead leaves or stones, brickwork, a clump of shrubs: all are crossed without any marked preference for one sort of road rather than another.
What is rigidly fixed is the path home, which follows the outward track in all its windings and all its crossings, however difficult. Laden with their plunder, the Red Ants return to the nest by the same road, often an exceedingly complicated one, which the exigencies of the chase compelled them to take originally. They repass each spot which they passed at first; and this is to them a matter of such imperative necessity that no additional fatigue nor even the gravest danger can make them alter the track.
Let us suppose that they have crossed a thick heap of dead leaves, representing to them a path beset with yawning gulfs, where every moment some one falls, where many are exhausted as they struggle out of the hollows and reach the heights by means of swaying bridges, emerging at last from the labyrinth of lanes. No matter: on their return, they will not fail, though weighed down with their burden, once more to struggle through that weary maze. To avoid all this fatigue, they would have but to swerve slightly from the original path, for the good, smooth road is there, hardly a step away. This little deviation never occurs to them.
I came upon them one day when they were on one of their raids. They were marching along the inner edge of the stone-work of the garden-pond, where I have replaced the old batrachians by a colony of Gold-fish. The wind was blowing very hard from the north and, taking the column in flank, sent whole rows of the Ants flying into the water. The fish hurried up; they watched the performance and gobbled up the drowning insects. It was a difficult bit; and the column was decimated before it had passed. I expected to see the return journey made by another road, which would wind round and avoid the fatal cliff. Not at all. The nymph-laden band resumed the parlous path and the Goldfish received a double windfall: the Ants and their prizes. Rather than alter its track, the column was decimated a second time.
It is not easy to find the way home again after a distant expedition, during which there have been various sorties, nearly always by different paths; and this difficulty makes it absolutely necessary for the Amazons to return by the same road by which they went. The insect has no choice of route, if it would not be lost on the way: it must come back by the track which it knows and which it has lately travelled. The Processionary Caterpillars, when they leave their nest and go to another branch, on another tree, in search of a type of leaf more to their taste, carpet the course with silk and are able to return home by following the threads stretched along their road. This is the most elementary method open to the insect liable to stray on its excursions: a silken path brings it home again. The Processionaries, with their unsophisticated traffic-laws, are very different from the Mason-bees and others, who have a special sense to guide them.
The Amazon, though belonging to the Hymenopteron clan, herself possesses rather limited homing-faculties, as witness her compulsory return by her former trail. Can she imitate, to a certain extent, the Processionaries' method, that is to say, does she leave, along the road traversed, not a series of conducting threads, for she is not equipped for that work, but some odorous emanation, for instance some formic scent, which would allow her to guide herself by means of the olfactory sense? This view is pretty generally accepted. The Ants, people say, are guided by the sense of smell; and this sense of smell appears to have its seat in the antennae, which we see in continual palpitation. It is doubtless very reprehensible, but I must admit that the theory does not inspire me with overwhelming enthusiasm. In the first place, I have my suspicions about a sense of smell seated in the antennae: I have given my reasons before; and, next, I hope to prove by experiment that the Red Ants are not guided by a scent of any kind.
To lie in wait for my Amazons, for whole afternoons on end, often unsuccessfully, meant taking up too much of my time. I engaged an assistant whose hours were not so much occupied as mine. It was my grand-daughter Lucie, a little rogue who liked to hear my stories of the Ants. She had been present at the great battle between the reds and blacks and was much impressed by the rape of the long-clothes babies. Well-coached in her exalted functions, very proud of already serving that august lady, Science, my little Lucie would wander about the garden, when the weather seemed propitious, and keep an eye on the Red Ants, having been commissioned to reconnoitre carefully the road to the pillaged Ant-hill. She had given proof of her zeal; I could rely upon it.
One day, while I was spinning out my daily quota of prose, there came a banging at my study-door:
‚It‘s I, Lucie! Come quick: the reds have gone into the blacks' house. Come quick!'
‚And do you know the road they took?‘
‚Yes, I marked it.‘
‚What! Marked it? How?‘
‚I did what Hop-o‘-my-Thumb did: I scattered little white stones along the road.'
I hurried out. Things had happened as my six-year-old colleague said. Lucie had secured her provision of pebbles in advance and, on seeing the Amazon regiment leave barracks, had followed them step by step and placed her stones at intervals along the road covered. The Ants had made their raid and were beginning to return along the track of tell-tale pebbles. The distance to the nest was about a hundred paces, which gave me time to make preparations for an experiment previously contemplated.
I take a big broom and sweep the track for about a yard across. The dusty particles on the surface are thus removed and replaced by others. If they were tainted with any odorous effluvia, their absence will throw the Ants off the track. I divide the road, in this way, at four different points, a few feet a part.
The column arrives at the first section. The hesitation of the Ants is evident. Some recede and then return, only to recede once more; others wander along the edge of the cutting; others disperse sideways and seem to be trying to skirt the unknown country. The head of the column, at first closed up to a width of a foot or so, now scatters to three or four yards. But fresh arrivals gather in their numbers before the obstacle; they form a mighty array, an undecided horde. At last, a few Ants venture into the swept zone and others follow, while a few have meantime gone ahead and recovered the track by a circuitous route. At the other cuttings, there are the same halts, the same hesitations; nevertheless, they are crossed, either in a straight line or by going round. In spite of my snares, the Ants manage to return to the nest; and that by way of the little stones.
The result of the experiment seems to argue in favour of the sense of smell. Four times over, there are manifest hesitations wherever the road is swept. Though the return takes place, nevertheless, along the original track, this may be due to the uneven work of the broom, which has left certain particles of the scented dust in position. The Ants who went round the cleared portion may have been guided by the sweepings removed to either side. Before, therefore, pronouncing judgment for or against the sense of smell, it were well to renew the experiment under better conditions and to remove everything containing a vestige of scent.
A few days later, when I have definitely decided on my plan, Lucie resumes her watch and soon comes to tell me of a sortie. I was counting on it, for the Amazons rarely miss an expedition during the hot and sultry afternoons of June and July, especially when the weather threatens storm. Hop-o'-my-Thumb's pebbles once more mark out the road, on which I choose the point best-suited to my schemes.
A garden-hose is fixed to one of the feeders of the pond; the sluice is opened; and the Ants' path is cut by a continuous torrent, two or three feet wide and of unlimited length. The sheet of water flows swiftly and plentifully at first, so as to wash the ground well and remove anything that may possess a scent. This thorough washing lasts for nearly a quarter of an hour. Then, when the Ants draw near, returning from the plunder, I let the water flow more slowly and reduce its depth, so as not to overtax the strength of the insects. Now we have an obstacle which the Amazons must surmount, if it is absolutely necessary for them to follow the first trail.
This time, the hesitation lasts long and the stragglers have time to come up with the head of the column. Nevertheless, an attempt is made to cross the torrent by means of a few bits of gravel projecting above the water; then, failing to find bottom, the more reckless of the Ants are swept off their feet and, without loosing hold of their prizes, drift away, land on some shoal, regain the bank and renew their search for a ford. A few straws borne on the waters stop and become so many shaky bridges on which the Ants climb. Dry olive-leaves are converted into rafts, each with its load of passengers. The more venturesome, partly by their own efforts, partly by good luck, reach the opposite bank without adventitious aid. I see some who, dragged by the current to one or the other bank, two or three yards off, seem very much concerned as to what they shall do next. Amid this disorder, amid the dangers of drowning, not one lets go her booty. She would not dream of doing so: death sooner than that! In a word, the torrent is crossed somehow or other along the regular track.
The scent of the road cannot be the cause of this, it seems to me, for the torrent not only washed the ground some time beforehand but also pours fresh water on it all the time that the crossing is taking place. Let us now see what will happen when the formic scent, if there really be one on the trail, is replaced by another, much stronger odour, one perceptible to our own sense of smell, which the first is not, at least not under present conditions.
I wait for a third sortie and, at one point in the road taken by the Ants, rub the ground with some handfuls of freshly gathered mint. I cover the track, a little farther on, with the leaves of the same plant. The Ants, on their return, cross the section over which the mint was rubbed without apparently giving it a thought; they hesitate in front of the section heaped up with leaves and then go straight on.
After these two experiments, first with the torrent of water which washes away all traces of smell from the ground and then with the mint which changes the smell, I think that we are no longer at liberty to quote scent as the guide of the Ants that return to the nest by the road which they took at starting. Further tests will tell us more about it.
Without interfering with the soil, I now lay across the track some large sheets of paper, newspapers, keeping them in position with a few small stones. In front of this carpet, which completely alters the appearance of the road, without removing any sort of scent that it may possess, the Ants hesitate even longer than before any of my other snares, including the torrent. They are compelled to make manifold attempts, reconnaissances to right and left, forward movements and repeated retreats, before venturing altogether into the unknown zone. The paper straits are crossed at last and the march resumed as usual.
Another ambush awaits the Amazons some distance farther on. I have divided the track by a thin layer of yellow sand, the ground itself being grey. This change of colour alone is enough for a moment to disconcert the Ants, who again hesitate in the same way, though not for so long, as they did before the paper. Eventually, this obstacle is overcome like the others.
As neither the stretch of sand nor the stretch of paper got rid of any scented effluvia with which the trail may have been impregnated, it is patent that, as the Ants hesitated and stopped in the same way as before, they find their way not by sense of smell, but really and truly by sense of sight; for, every time that I alter the appearance of the track in any way whatever — whether by my destructive broom, my streaming water, my green mint, my paper carpet or my golden sand — the returning column calls a halt, hesitates and attempts to account for the changes that have taken place. Yes, it is sight, but a very dull sight, whose horizon is altered by the shifting of a few bits of gravel. To this short sight, a strip of paper, a bed of mint-leaves, a layer of yellow sand, a stream of water, a furrow made by the broom, or even lesser modifications are enough to transform the landscape; and the regiment, eager to reach home as fast as it can with its loot, halts uneasily on beholding this unfamiliar scenery. If the doubtful zones are at length passed, it is due to the fact that fresh attempts are constantly being made to cross the doctored strips and that at last a few Ants recognize well-known spots beyond them. The others, relying on their clearer-sighted sisters, follow.
Sight would not be enough, if the Amazon had not also at her service a correct memory for places. The memory of an Ant! What can that be? In what does it resemble ours? I have no answers to these questions; but a few words will enable me to prove that the insect has a very exact and persistent recollection of places which it has once visited. Here is something which I have often witnessed. It sometimes happens that the plundered Ant-hill offers the Amazons a richer spoil than the invading column is able to carry away. Or, again, the region visited is rich in Ant-hills. Another raid is necessary, to exploit the site thoroughly. In such cases, a second expedition takes place, sometimes on the next day, sometimes two or three days later. This time, the column does no reconnoitring on the way: it goes straight to the spot known to abound in nymphs and travels by the identical path which it followed before. It has sometimes happened that I have marked with small stones, for a distance of twenty yards, the road pursued a couple of days earlier and have then found the Amazons proceeding by the same route, stone by stone:
‚They will go first here and then there,‘ I said, according to the position of the guide-stones.
And they would, in fact, go first here and then there, skirting my line of pebbles, without any noticeable deviation.
Can one believe that odoriferous emanations diffused along the route are going to last for several days? No one would dare to suggest it. It must, therefore, be sight that directs the Amazons, sight assisted by a memory for places. And this memory is tenacious enough to retain the impression until the next day and later; it is scrupulously faithful, for it guides the column by the same path as on the day before, across the thousand irregularities of the ground.
How will the Amazon behave when the locality is unknown to her? Apart from topographical memory, which cannot serve her here, the region in which I imagine her being still unexplored, does the Ant possess the Mason-bee's sense of direction, at least within modest limits, and is she able thus to regain her Ant-hill or her marching column?
The different parts of the garden are not all visited by the marauding legions to the same extent: the north side is exploited by preference, doubtless because the forays in that direction are more productive. The Amazons, therefore, generally direct their troops north of their barracks; I seldom see them in the south. This part of the garden is, if not wholly unknown, at least much less familiar to them than the other. Having said that, let us observe the conduct of the strayed Ant.
I take up my position near the Ant-hill; and, when the column returns from the slave-raid, I force an Ant to step on a leaf which I hold out to her. Without touching her, I carry her two or three paces away from her regiment: no more than that, but in a southerly direction. It is enough to put her astray, to make her lose her bearings entirely. I see the Amazon, now replaced on the ground, wander about at random, still, I need hardly say, with her booty in her mandibles; I see her hurry away from her comrades, thinking that she is rejoining them; I see her retrace her steps, turn aside again, try to the right, try to the left and grope in a host of directions, without succeeding in finding her whereabouts. The pugnacious, strong-jawed slave-hunter is utterly lost two steps away from her party. I have in mind certain strays who, after half an hour's searching, had not succeeded in recovering the route and were going farther and farther from it, still carrying the nymph in their teeth. What became of them? What did they do with their spoil? I had not the patience to follow those dull-witted marauders to the end.
Let us repeat the experiment, but place the Amazon to the north. After more or less prolonged hesitations, after a search now in this direction, now in that, the Ant succeeds in finding her column. She knows the locality.
Here, of a surety, is a Hymenopteron deprived of that sense of direction which other Hymenoptera enjoy. She has in her favour a memory for places and nothing more. A deviation amounting to two or three of our strides is enough to make her lose her way and to keep her from returning to her people, whereas miles across unknown country will not foil the Mason-bee. I expressed my surprise, just now, that man was deprived of a wonderful sense wherewith certain animals are endowed. The enormous distance between the two things compared might furnish matter for discussion. In the present case, the distance no longer exists: we have to do with two insects very near akin, two Hymenoptera. Why, if they issue from the same mould, has one a sense which the other has not, an additional sense, constituting a much more overpowering factor than the structural details? I will wait until the evolutionists condescend to give me a valid reason.
To return to this memory for places whose tenacity and fidelity I have just recognized: to what degree does it consent to retain impressions? Does the Amazon require repeated journeys in order to learn her geography, or is a single expedition enough for her? Are the line followed and the places visited engraved on her memory from the first? The Red Ant does not lend herself to the tests that might furnish the reply: the experimenter is unable to decide whether the path followed by the expeditionary column is being covered for the first time, nor is it in his power to compel the legion to adopt this or that different road. When the Amazons go out to plunder the Ant-hills, they take the direction which they please; and we are not allowed to interfere with their march. Let us turn to other Hymenoptera for information.
I select the Pompili, whose habits we shall study in detail in a later chapter (6). They are hunters of Spiders and diggers of burrows. The game, the food of the coming larva, is first caught and paralysed; the home is excavated afterwards. As the heavy prey would be a grave encumbrance to the Wasp in search of a convenient site, the Spider is placed high up, on a tuft of grass or brushwood, out of the reach of marauders, especially Ants, who might damage the precious morsel in the lawful owner's absence. After fixing her booty on the verdant pinnacle, the Pompilus casts around for a favourable spot and digs her burrow. During the process of excavation, she returns from time to time to her Spider; she nibbles at the prize, feels, touches it here and there, as though taking stock of its plumpness and congratulating herself on the plentiful provender; then she returns to her burrow and goes on digging. Should anything alarm or distress her, she does not merely inspect her Spider: she also brings her a little closer to her work-yard, but never fails to lay her on the top of a tuft of verdure. These are the manoeuvres of which I can avail myself to gauge the elasticity of the Wasp's memory.
While the Pompilus is at work on the burrow, I seize the prey and place it in an exposed spot, half a yard away from its original position. The Pompilus soon leaves the hole to enquire after her booty and goes straight to the spot where she left it. This sureness of direction, this faithful memory for places can be explained by repeated previous visits. I know nothing of what has happened beforehand. Let us take no notice of this first expedition; the others will be more conclusive. For the moment, the Pompilus, without the least hesitation, finds the tuft of grass whereon her prey was lying. Then come marches and counter-marches upon that tuft, minute explorations and frequent returns to the exact spot where the Spider was deposited. At last, convinced that the prize is no longer there, the Wasp makes a leisurely survey of the neighbourhood, feeling the ground with her antennae as she goes. The Spider is descried in the exposed spot where I had placed her. Surprise on the part of the Pompilus, who goes forward and then suddenly steps back with a start:
‚Is it alive?‘ she seems to ask. ‚Is it dead? Is it really my Spider? Let us be wary!‘
The hesitation does not last long: the huntress grabs her victim, drags her backwards and places her, still high up, on a second tuft of herbage, two or three steps away from the first. She then goes back to the burrow and digs for a while. For the second time, I remove the Spider and lay her at some distance, on the bare ground. This is the moment to judge of the Wasp's memory. Two tufts of grass have served as temporary resting-places for the game. The first, to which she returned with such precision, the Wasp may have learnt to know by a more or less thorough examination, by reiterated visits that escaped my eye; but the second has certainly made but a slight impression on her memory. She adopted it without any studied choice; she stopped there just long enough to hoist her Spider to the top; she saw it for the first time and saw it hurriedly, in passing. Is that rapid glance enough to provide an exact recollection? Besides, there are now two localities to be modelled in the insect's memory: the first shelf may easily be confused with the second. To which will the Pompilus go?
We shall soon find out: here she comes, leaving the burrow to pay a fresh visit to the Spider. She runs straight to the second tuft, where she hunts about for a long time for her absent prey. She knows that it was there, when last seen, and not elsewhere; she persists in looking for it there and does not once think of going back to the first perch. The first tuft of grass no longer counts; the second alone interests her. And then the search in the neighbourhood begins again.
On finding her game on the bare spot where I myself have placed it, the Pompilus quickly deposits the Spider on a third tuft of grass; and the experiment is renewed. This time, the Pompilus hurries to the third tuft when she comes to look after her Spider; she hurries to it without hesitation, without confusing it in any way with the first two, which she scorns to visit, so sure is her memory. I do the same thing a couple of times more; and the insect always returns to the last perch, without worrying about the others. I stand amazed at the memory of that pigmy. She need but catch a single hurried glimpse of a spot that differs in no wise from a host of others in order to remember it quite well, notwithstanding the fact that, as a miner relentlessly pursuing her underground labours, she has other matters to occupy her mind. Could our own memory always vie with hers? It is very doubtful. Allow the Red Ant the same sort of memory; and her peregrinations, her returns to the nest by the same road are no longer difficult to explain.
Tests of this kind have furnished me with some other results worthy of mention. When convinced, by untiring explorations, that her prey is no longer on the tuft where she laid it, the Pompilus, as we were saying, looks for it in the neighbourhood and finds it pretty easily, for I am careful to put it in an exposed place. Let us increase the difficulty to some extent. I dig the tip of my finger into the ground and lay the Spider in the little hole thus obtained, covering her with a tiny leaf. Now the Wasp, while in quest of her lost prey, happens to walk over this leaf, to pass it again and again without suspecting that the Spider lies beneath, for she goes and continues her vain search farther off. Her guide, therefore is not scent, but sight. Nevertheless, she is constantly feeling the ground with her antennae. What can be the function of those organs? I do not know, although I assert that they are not olfactory organs. The Ammophila, in search of her Grey Worm, had already led me to make the same assertion; I now obtain an experimental proof which seems to me decisive. I would add that the Pompilus has very short sight: often she passes within a couple of inches of her Spider without seeing her.
1. Alphonse Toussenel (1803–1885), the author of a number of interesting and valuable works on ornithology.
2. A Sand-wasp who hunts the Grey Worm, or Caterpillar of the Turnip-moth, to serve as food for her grubs. For other varieties of the Ammophila, cf. „Insect Life“: chapter 15.
3. Another Hunting Wasp, who feeds her young on Weevils. Cf. „Insect Life“: chapters 4 and 5.
4. „Insect Life“: chapter 19.
5. The Hymenoptera are an order of insects having four membranous wings and include the Bees, Wasps, Ants, Saw-flies and Ichneumon-flies.
6. For the Wasp known as the Pompilus, or Ringed Calicurgus, cf. „The Life and Love of the Insect“, by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chapter 12.