Chapter XIV. The Halicti: Parthenogenesis
Sweat Bee (Halictus rubicundus)
The Halictus opens up another question, connected with one of life's obscurest problems. Let us go back five-and-twenty years. I am living at Orange. My house stands alone among the fields. On the other side of the wall enclosing our yard, which faces due south, is a narrow path overgrown with couch-grass. The sun beats full upon it; and the glare reflected from the whitewash of the wall turns it into a little tropical corner, shut off from the rude gusts of the north-west wind.
Here the Cats come to take their afternoon nap, with their eyes half-closed; here the children come, with Bull, the House-dog; here also come the haymakers, at the hottest time of the day, to sit and take their meal and whet their scythes in the shade of the plane-tree; here the women pass up and down with their rakes, after the hay-harvest, to glean what they can on the niggardly carpet of the shorn meadow. It is therefore a very much frequented footpath, were it only because of the coming and going of our household: a thoroughfare ill-suited, one would think, to the peaceful operations of a Bee; and nevertheless it is such a very warm and sheltered spot and the soil is so favourable that every year I see the Cylindrical Halictus (H. cylindricus, FAB.) hand down the site from one generation to the next. It is true that the very matutinal, even partly nocturnal character of the work makes the insect suffer less inconvenience from the traffic.
The burrows cover an extent of some ten square yards, and their mounds, which often come near enough to touch, average a distance of four inches at the most from one another. Their number is therefore something like a thousand. The ground just here is very rough, consisting of stones and dust mixed with a little mould and held together by the closely interwoven roots of the couch-grass. But, owing to its nature, it is thoroughly well drained, a condition always in request among Bees and Wasps that have underground cells.
Let us forget for a moment what the Zebra Halictus and the Early Halictus have taught us. At the risk of repeating myself a little, I will relate what I observed during my first investigations. The Cylindrical Halictus works in May. Except among the social species, such as Common Wasps, Bumble-bees, Ants and Hive-bees, it is the rule for each insect that victuals its nests either with honey or game to work by itself at constructing the home of its grubs. Among insects of the same species there is often neighbourship; but their labours are individual and not the result of co-operation. For instance, the Cricket-hunters, the Yellow-winged Sphex, settle in gangs at the foot of a sandstone cliff, but each digs her own burrow and would not suffer a neighbour to come and help in piercing the home.
In the case of the Anthophorae, an innumerable swarm takes possession of a sun-scorched crag, each Bee digging her own gallery and jealously excluding any of her fellows who might venture to come to the entrance of her hole. The Three-pronged Osmia, when boring the bramble-stalk tunnel in which her cells are to be stacked, gives a warm reception to any Osmia that dares set foot upon her property.
Let one of the Odyneri who make their homes in a road-side bank mistake the door and enter her neighbour's house: she would have a bad time of it! Let a Megachile, returning with her leafy disk in her legs, go into the wrong basement: she would be very soon dislodged! So with the others: each has her own home, which none of the others has the right to enter. This is the rule, even among Bees and Wasps established in a populous colony on a common site. Close neighbourhood implies no sort of intimate relationship.
Great therefore is my surprise as I watch the Cylindrical Halictus' operations. She forms no society, in the entomological sense of the word: there is no common family; and the general interest does not engross the attention of the individual. Each mother occupies herself only with her own eggs, builds cells and gathers honey only for her own larvae, without concerning herself in any way with the upbringing of the others' grubs. All that they have in common is the entrance-door and the goods-passage, which ramifies in the ground and leads to different groups of cells, each the property of one mother. Even so, in the blocks of flats in our large towns, one door, one hall and one staircase lead to different floors or different portions of a floor where each family retains its isolation and its independence.
This common right of way is extremely easy to perceive at the time for victualling the nests. Let us direct our attention for a while to the same entrance-aperture, opening at the top of a little mound of earth freshly thrown up, like that accumulated by the Ants during their works. Sooner or later we shall see the Halicti arrive with their load of pollen, gathered on the Cichoriaceae of the neighbourhood.
Usually, they come up one by one; but it is not rare to see three, four or even more appearing at the same time at the mouth of one burrow. They perch on the top of the mound and, without hurrying in front of one another, with no sign of jealousy, they dive down the passage, each in her turn. We need but watch their peaceful waiting, their tranquil dives, to recognize that this indeed is a common passage to which each has as much right as another.
When the soil is exploited for the first time and the shaft sunk slowly from the outside to the inside, do several Cylindrical Halicti, one relieving the other, take part in the work by which they will afterwards profit equally? I do not believe it for a moment. As the Zebra Halictus and the Early Halictus told me later, each miner goes to work alone and makes herself a gallery which will be her exclusive property. The common use of the passage comes presently, when the site, tested by experience, is handed down from one generation to another.
A first group of cells is established, we will suppose, at the bottom of a pit dug in virgin soil. The whole thing, cells and pit, is the work of one insect. When the moment comes to leave the underground dwelling, the Bees emerging from this nest will find before them an open road, or one at most obstructed by crumbly matter, which offers less resistance than the neighbouring soil, as yet untouched. The exit-way will therefore be the primitive way, contrived by the mother during the construction of the nest. All enter upon it without any hesitation, for the cells open straight on it. All, coming and going from the cells to the bottom of the shaft and from the shaft to the cells, will take part in the clearing, under the stimulus of the approaching deliverance.
It is quite unnecessary here to presume among these underground prisoners a concerted effort to liberate themselves more easily by working in common: each is thinking only of herself and invariably returns, after resting, to toil at the inevitable path, the path of least resistance, in short the passage once dug by the mother and now more or less blocked up.
Among the Cylindrical Halicti, any one who wishes emerges from her cell at her own hour, without waiting for the emergence of the others, because the cells, grouped in small stacks, have each their special outlet opening into the common gallery. The result of this arrangement is that all the inhabitants of one burrow are able to assist, each doing her share, in the clearing of the exit-shaft. When she feels fatigued, the worker retires to her undamaged cell and another succeeds her, impatient to get out rather than to help the first. At last the way is clear and the Halicti emerge. They disperse over the flowers around as long as the sun is hot; when the air cools, they go back to the burrows to spend the night there.
A few days pass and already the cares of egg-laying are at hand. The galleries have never been abandoned. The Bees have come to take refuge there on rainy or very windy days; most, if not all, have returned every evening at sunset, each doubtless making for her own cell, which is still intact and which is carefully impressed upon her memory. In a word, the Cylindrical Halictus does not lead a wandering life; she has a fixed residence.
A necessary consequence results from these settled habits: for the purpose of her laying, the Bee will adopt the identical burrow in which she was born. The entrance-gallery is ready therefore. Should it need to be carried deeper, to be pushed in new directions, the builder has but to extend it at will. The old cells even can serve again, if slightly restored.
Thus resuming possession of the native burrow in view of her offspring, the Bee, notwithstanding her instincts as a solitary worker, achieves an attempt at social life, because there is one entrance-door and one passage for the use of all the mothers returning to the original domicile. There is thus a semblance of collaboration without any real co-operation for the common weal. Everything is reduced to a family inheritance shared equally among the heirs.
The number of these coheirs must soon be limited, for a too tumultuous traffic in the corridor would delay the work. Then fresh passages are opened inwards, often communicating with depths already excavated, so that the ground at last is perforated in every direction with an inextricable maze of winding tunnels.
The digging of the cells and the piercing of new galleries take place especially at night. A cone of fresh earth on top of the burrow bears evidence every morning to the overnight activity. It also shows by its volume that several navvies have taken part in the work, for it would be impossible for a single Halictus to extract from the ground, convey to the surface and heap up so large a stack of rubbish in so short a time.
At sunrise, when the fields around are still wet with dew, the Cylindrical Halictus leaves her underground passages and starts on her foraging. This is done without animation, perhaps because of the morning coolness. There is no joyous excitement, no humming above the burrows. The Bees come back again, flying low, silently and heavily, their hind-legs yellow with pollen; they alight on the earth-cone and at once dive down the vertical chimney. Others come up the pipe and go off to their harvesting.
This journeying to and fro for provisions continues until eight or nine in the morning. Then the heat begins to grow intense and is reflected by the wall; then also the path is once more frequented. People pass at every moment, coming out of the house or elsewhence. The soil is so much trodden under foot that the little mounds of refuse surrounding each burrow soon disappear and the site loses every sign of underground habitation.
All day long, the Halicti remain indoors. Withdrawing to the bottom of the galleries, they occupy themselves probably in making and polishing the cells. Next morning, new cones of rubbish appear, the result of the night's work, and the pollen-harvest is resumed for a few hours; then everything ceases again. And so the work goes on, suspended by day, renewed at night and in the morning hours, until completely finished.
The passages of the Cylindrical Halictus descend to a depth of some eight inches and branch into secondary corridors, each giving access to a set of cells. These number six or eight to each set and are ranged side by side, parallel with their main axis, which is almost horizontal. They are oval at the base and contracted at the neck. Their length is nearly twenty millimetres (1) and their greatest width eight (2). They do not consist simply of a cavity in the ground; on the contrary, they have their own walls, so that the group can be taken out in one piece, with a little precaution, and removed neatly from the earth in which it is contained.
The walls are formed of fairly delicate materials, which must have been chosen in the coarse surrounding mass and kneaded with saliva. The inside is carefully polished and upholstered with a thin waterproof film. We will cut short these details concerning the cells, which the Zebra Halictus has already shown us in greater perfection, leave the home to itself and come to the most striking feature in the life-history of the Halicti.
The Cylindrical Halictus is at work in the first days of May. It is a rule among the Hymenoptera for the males never to take part in the fatiguing work of nest-building. To construct cells and to amass victuals are occupations entirely foreign to their nature. This rule seems to have no exceptions; and the Halicti conform to it like the rest. It is therefore only to be expected that we should see no males shooting the underground rubbish outside the galleries. That is not their business.
But what does astonish us, when our attention is directed to it, is the total absence of any males in the vicinity of the burrows. Although it is the rule that the males should be idle, it is also the rule for these idlers to keep near the galleries in course of construction, coming and going from door to door and hovering above the work-yards to seize the moment at which the unfecundated females will at last yield to their importunities.
Now here, despite the enormous population, despite my careful and incessant watch, it is impossible for me to distinguish a single male. And yet the distinction between the sexes is of the simplest. It is not necessary to take hold of the male. He can be recognized even at a distance by his slenderer frame, by his long, narrow abdomen, by his red sash. They might easily suggest two different species. The female is a pale russet-brown; the male is black, with a few red segments to his abdomen. Well, during the May building-operations, there is not a Bee in sight clad in black, with a slender, red-belted abdomen; in short, not a male.
Though the males do not come to visit the environs of the burrows, they might be elsewhere, particularly on the flowers where the females go plundering. I did not fail to explore the fields, insect-net in hand. My search was invariably fruitless. On the other hand, those males, now nowhere to be found, are plentiful later, in September, along the borders of the paths, on the close-set flowers of the eringo.
This singular colony, reduced exclusively to mothers, made me suspect the existence of several generations a year, whereof one at least must possess the other sex. I continued therefore, when the building, who was over, to keep a daily watch on the establishment of the Cylindrical Halictus, in order to seize the favourable moment that would verify my suspicions. For six weeks, solitude reigned above the burrows: not a single Halictus appeared; and the path, trodden by the wayfarers, lost its little heaps of rubbish, the only signs of the excavations. There was nothing outside to show that the warmth down below was hatching populous swarms.
July comes and already a few little mounds of fresh earth betoken work going on underground in preparation for an exodus in the near future. As the males, among the Hymenoptera, are generally further advanced than the females and quit their natal cells earlier, it was important that I should witness the first exits made, so as to dispel the least shadow of a doubt. A violent exhumation would have a great advantage over the natural exit: it would place the population of the burrows immediately under my eyes, before the departure of either sex. In this way, nothing could escape from me and I was dispensed from a watch which, for all its attentiveness, was not to be relied upon absolutely. I therefore resolve upon a reconnaissance with the spade.
I dig down to the full depth of the galleries and remove large lumps of earth which I take in my hands and break very carefully so as to examine all the parts that may contain cells. Halicti in the perfect state predominate, most of them still lodged in their unbroken chambers. Though they are not quite so numerous, there are also plenty of pupae. I collect them of every shade of colour, from dead-white, the sign of a recent transformation, to smoky-brown, the mark of an approaching metamorphosis. Larvae, in small quantities, complete the harvest. They are in the state of torpor that precedes the appearance of the pupa.
I prepare boxes with a bed of fresh, sifted earth to receive the larvae and the pupae, which I lodge each in a sort of half-cell formed by the imprint of my finger. I will await the transformation to decide to which sex they belong. As for the perfect insects, they are inspected, counted and at once released.
In the very unlikely supposition that the distribution of the sexes might vary in different parts of the colony, I make a second excavation, at a few yards' distance from the other. It supplies me with another collection both of perfect insects and of pupae and larvae.
When the metamorphosis of the laggards is completed, which does not take many days, I proceed to take a general census. It gives me two hundred and fifty Halicti. Well, in this number of Bees, collected in the burrow before any have emerged, I perceive none, absolutely none but females; or, to be mathematically accurate, I find just one male, one alone; and he is so small and feeble that he dies without quite succeeding in divesting himself of his nymphal bands. This solitary male is certainly accidental. A female population of two hundred and forty-nine Halicti implies other males than this abortion, or rather implies none at all. I therefore eliminate him as an accident of no value and conclude that, in the Cylindrical Halictus, the July generation consists of females only.
The building-operations start again in the second week of July. The galleries are restored and lengthened; new cells are fashioned and the old ones repaired. Follow the provisioning, the laying of the eggs, the closing of the cells; and, before July is over, there is solitude again. Let me also say that, during the building-period, not a male appears in sight, a fact which adds further proof to that already supplied by my excavations.
With the high temperature of this time of the year, the development of the larvae makes rapid progress: a month is sufficient for the various stages of the metamorphosis. On the 24th of August there are once more signs of life above the burrows of the Cylindrical Halictus, but under very different conditions. For the first time, both sexes are present. Males, so easily recognized by their black livery and their slim abdomen adorned with a red ring, hover backwards and forwards, almost level with the ground. They fuss about from burrow to burrow. A few rare females come out for a moment and then go in again.
I proceed to make an excavation with my spade; I gather indiscriminately whatever I come across. Larvae are very scarce; pupae abound, as do perfect insects. The list of my captures amounts to eighty males and fifty-eight females. The males, therefore, hitherto impossible to discover, either on the flowers around or in the neighbourhood of the burrows, could be picked up to-day by the hundred, if I wished. They outnumber the females by about four to three; they are also further developed, in accordance with the general rule, for most of the backward pupae give me only females.
Once the two sexes had appeared, I expected a third generation that would spend the winter in the larval state and recommence in May the annual cycle which I have just described. My anticipation proved to be at fault. Throughout September, when the sun beats upon the burrows, I see the males flitting in great numbers from one shaft to the other. Sometimes a female appears, returning from the fields, but with no pollen on her legs. She seeks her gallery, finds it, dives down and disappears.
The males, as though indifferent to her arrival, offer her no welcome, do not harass her with their amorous pursuits; they continue to visit the doors of the burrows with a winding and oscillating flight. For two months, I follow their evolutions. If they set foot on earth, it is to descend forthwith into some gallery that suits them.
It is not uncommon to see several of them on the threshold of the same burrow. Then each awaits his turn to enter; they are as peaceable in their relations as the females who are joint owners of a burrow. At other times, one wants to go in as a second is coming out. This sudden encounter produces no strife. The one leaving the hole withdraws a little to one side to make enough room for two; the other slips past as best he can. These peaceful meetings are all the more striking when we consider the usual rivalry between males of the same species.
No rubbish-mound stands at the mouth of the shafts, showing that the building has not been resumed; at the most, a few crumbs of earth are heaped outside. And by whom, pray? By the males and by them alone. The lazy sex has bethought itself of working. It turns navvy and shoots out grains of earth that would interfere with its continual entrances and exits. For the first time I witness a custom which no Hymenopteron had yet shown me: I see the males haunting the interior of the burrows with an assiduity equalling that of the mothers employed in nest-building.
The cause of these unwonted operations soon stands revealed. The females seen flitting above the burrows are very rare; the majority of the feminine population remain sequestered under ground, do not perhaps come out once during the whole of the latter part of summer. Those who do venture out go in again soon, empty-handed of course and always without any amorous teasing from the males, a number of whom are hovering above the burrows.
On the other hand, watch as carefully as I may, I do not discover a single act of pairing out of doors. The weddings are clandestine, therefore, and take place under ground. This explains the males' fussy visits to the doors of the galleries during the hottest hours of the day, their continual descents into the depths and their continual reappearances. They are looking for the females cloistered in the retirement of the cells.
A little spade-work soon turns suspicion into certainty. I unearth a sufficient number of couples to prove to me that the sexes come together underground. When the marriage is consummated, the red-belted one quits the spot and goes to die outside the burrow, after dragging from flower to flower the bit of life that remains to him. The other shuts herself up in her cell, there to await the return of the month of May.
September is spent by the Halictus solely in nuptial celebrations. Whenever the sky is fine, I witness the evolutions of the males above the burrows, with their continual entrances and exits; should the sun be veiled, they take refuge down the passages. The more impatient, half-hidden in the pit, show their little black heads outside, as though peeping for the least break in the clouds that will allow them to pay a brief visit to the flowers round about. They also spend the night in the burrows. In the morning, I attend their levee; I see them put their head to the window, take a look at the weather and then go in again until the sun beats on the encampment.
The same mode of life is continued throughout October, but the males become less numerous from day to day as the stormy season approaches and fewer females remain to be wooed. By the time that the first cold weather comes, in November, complete solitude reigns over the burrows. I once more have recourse to the spade. I find none but females in their cells. There is not one male left. All have vanished, all are dead, the victims of their life of pleasure and of the wind and rain. Thus ends the cycle of the year for the Cylindrical Halictus.
In February, after a hard winter, when the snow had lain on the ground for a fortnight, I wanted once more to look into the matter of my Halicti. I was in bed with pneumonia and at the point of death, to all appearances. I had little or no pain, thank God, but extreme difficulty in living. With the little lucidity left to me, being able to do no other sort of observing, I observed myself dying; I watched with a certain interest the gradual falling to pieces of my poor machinery. Were it not for the terror of leaving my family, who were still young, I would gladly have departed. The after-life must have so many higher and fairer truths to teach us.
My hour had not yet come. When the little lamps of thought began to emerge, all flickering, from the dusk of unconsciousness, I wished to take leave of the Hymenopteron, my fondest joy, and first of all of my neighbour, the Halictus. My son Emile took the spade and went and dug the frozen ground. Not a male was found, of course; but there were plenty of females, numbed with the cold in their cells.
A few were brought for me to see. Their little chambers showed no efflorescence of rime, with which all the surrounding earth was coated. The waterproof varnish had been wonderfully efficacious. As for the anchorites, roused from their torpor by the warmth of the room, they began to wander about my bed, where I followed them vaguely with my fading eyes.
May came, as eagerly awaited by the sick man as by the Halicti. I left Orange for Serignan, my last stage, I expect. While I was moving, the Bees resumed their building. I gave them a regretful glance, for I had still much to learn in their company. I have never since met with such a mighty colony.
These old observations on the habits of the Cylindrical Halictus may now be followed by a general summary which will incorporate the recent data supplied by the Zebra Halictus and the Early Halictus.
The females of the Cylindrical Halictus whom I unearth from November onwards are evidently fecundated, as is proved by the assiduity of the males during the preceding two months and most positively confirmed by the couples discovered in the course of my excavations. These females spend the winter in their cells, as do many of the early-hatching melliferous insects, such as Anthophorae and Mason-bees, who build their nests in the spring, the larvae reaching the perfect state in the summer and yet remaining shut up in their cells until the following May. But there is this great difference in the case of the Cylindrical Halictus, that in the autumn the females leave their cells for a time to receive the males under ground. The couples pair and the males perish. Left alone, the females return to their cells, where they spend the inclement season.
The Zebra Halicti, studied first at Orange and then, under better conditions, at Serignan, in my own enclosure, have not these subterranean customs: they celebrate their weddings amid the joys of the light, the sun and the flowers. I see the first males appear in the middle of September, on the centauries. Generally there are several of them courting the same bride. Now one, then another, they swoop upon her suddenly, clasp her, leave her, seize hold of her again. Fierce brawls decide who shall possess her. One is accepted and the others decamp. With a swift and angular flight, they go from flower to flower, without alighting. They hover on the wing, looking about them, more intent on pairing than on eating.
The Early Halictus did not supply me with any definite information, partly through my own fault, partly through the difficulty of excavation in a stony soil, which calls for the pick-axe rather than the spade. I suspect her of having the nuptial customs of the Cylindrical Halictus.
There is another difference, which causes certain variations of detail in these customs. In the autumn, the females of the Cylindrical Halictus leave their burrows seldom or not at all. Those who do go out invariably come back after a brief halt upon the flowers. All pass the winter in the natal cells. On the other hand, those of the Zebra Halictus move their quarters, meet the males outside and do not return to the burrows, which my autumn excavations always find deserted. They hibernate in the first hiding-places that offer.
In the spring, the females, fecundated since the autumn, come out: the Cylindrical Halicti from their cells, the Zebra Halicti from their various shelters, the Early Halicti apparently from their chambers, like the first. They work at their nests in the absence of any male, as do also the Social Wasps, whose whole brood has perished excepting a few mothers also fecundated in the autumn. In both cases, the assistance of the males is equally real, only it has preceded the laying by about six months.
So far, there is nothing new in the life of the Halicti; but here is where the unexpected appears: in July, another generation is produced; and this time without males. The absence of masculine assistance is no longer a mere semblance here, due to an earlier fecundation: it is a reality established beyond a doubt by the continuity of my observations and by my excavations during the summer season, before the emergence of the new Bees. At this period, a little before July, if my spade unearth the cells of any one of my three Halicti, the result is always females, nothing but females, with exceedingly rare exceptions.
True, it may be said that the second progeny is due to the mothers who knew the males in autumn and who would be able to nidify twice a year. The suggestion is not admissible. The Zebra Halictus confirms what I say. She shows us the old mothers no longer leaving the home but mounting guard at the entrance to the burrows. No harvesting- or pottery-work is possible with these absorbing doorkeeping-functions. Therefore there is no new family, even admitting that the mothers' ovaries are not depleted.
I do not know if a similar argument is valid in the case of the Cylindrical Halictus. Has she any general survivors? As my attention had not yet been directed on this point in the old days, when I had the insect at my door, I have no records to go upon. For all that, I am inclined to think that the portress of the Zebra Halictus is unknown here. The reason of this absence would be the number of workers at the start.
In May, the Zebra Halictus, living by herself in her winter retreat, founds her house alone. When her daughters succeed her, in July, she is the only grandmother in the establishment and the post of portress falls to her. With the Cylindrical Halictus, the conditions are different. Here the May workers are many in the same burrow, where they dwell in common during the winter. Supposing that they survive when the business of the household is finished, to whom will the office of overseer fall? Their number is so great and they are all so full of zeal that disorder would be inevitable. But we can leave this small matter unsettled pending further information.
The fact remains that females, females exclusively, have come out of the eggs laid in May. They have descendants, of that there is no room for doubt; they procreate though there are no males in their time.
From this generation by a single sex, there spring, two months later, males and females. These mate; and the same order of things recommences.
Sweat Bee (Halictus farinosus)
To sum up, judging by the three species that form the subject of my investigations, the Halicti have two generations a year: one in the spring, issuing from the mothers who have lived through the winter after being fecundated in the autumn; the other in the summer, the fruit of parthenogenesis, that is to say, of reproduction by the powers of the mother alone. Of the union of the two sexes, females alone are born; parthenogenesis gives birth at the same time to females and males.
When the mother, the original genitrix, has been able once to dispense with a coadjutor, why does she need one later? What is the puny idler there for? He was unnecessary. Why does he become necessary now? Shall we ever obtain a satisfactory answer to the question? It is doubtful. However, without much hope of succeeding we will one day consult the Gall-fly, who is better-versed than we in the tangled problem of the sexes.
1. .78 inch.
2. .312 inch.