The Mason-Bees Part 5

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 pa.s.sed. 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 a.s.sistant 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, p.r.o.nouncing 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 was.h.i.+ng 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 pa.s.sengers. The more venturesome, partly by their own efforts, partly by good luck, reach the opposite bank without advent.i.tious 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 s.h.i.+fting 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 pa.s.sed, 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 a.s.sisted 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, const.i.tuting 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. (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.--Translator's Note.) 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 enc.u.mbrance to the Wasp in search of a convenient site, the Spider is placed high up, on a tuft of gra.s.s 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 gra.s.s 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 gra.s.s 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 pa.s.sing. 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 gra.s.s 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 gra.s.s; 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.