THE KERMES OF THE OAK

The nest, that notable expression of maternal skill and care, is rivalled by other modes of rearing which often reveal the most wonderful tenderness. The Lycosa drags behind her, hanging to her spinnerets, the wallet of eggs that bangs against her legs; and for half the year she carries about on her back her young, fore-gathered in a serried group. In like fashion does the Scorpion nurse her offspring on her back; for a fortnight she allows them to gather strength against the moment of emancipation. Exuding a white wax, the Dorthesia contrives at the tip of the abdomen an exquisite [312]muff into which the young are born, and in which they adorn themselves with cottony tufts and peacefully grow ripe for the exodus. The downy refuge, with its narrow opening, allows the secluded offspring to emerge, one by one, as they become capable of settling down upon the fostering spurge.

Lowly among the lowliest, the Kermes of the oak has invented something even better: the mother, transformed into an unassailable fortress, bequeaths to her family, as its cradle, her skin, toughened into an ebony bastion.

In May let us patiently examine, in sunny corners, the slender twigs of the holm-oak or evergreen oak. Let us also inspect that cross-grained shrub with small prickly leaves, known to the Provençal peasant as the avaus, and to botanists as the kermes oak. This wretched brushwood, which one can pass over in a single stride, is really an oak, a genuine oak, as is proved by its handsome acorns, set in their rough, prickly cups. We will gather our harvest here as well as on the holm-oak. But we shall pass by the ordinary or English oak; we should find on it nothing in the least like what we [313]are seeking to-day. Only the two species first mentioned will repay exploration.

On these we shall see, a few here and a few there, but never in abundance, certain globules of a glossy black, about the bigness of a moderate-sized pea. Here we have the Kermes, one of the strangest of insects. But is this an insect? Is it of the animal kingdom? The uninitiated would never suspect such a thing; he would take the object for a berry, some species of black current. The mistake is all the more natural in that the globule, if bitten into, cracks, and yields a sweetish flavour, offset by a slight bitterness.

And this all but delicious fruit, we are told, is of the animal kingdom; it is an insect. Let us look at the creature closely, through the pocket microscope. We look for a head, an abdomen, and legs. There is absolutely not a vestige of a head, nor of an abdomen, nor of legs; all there is to be seen is a sort of large bead, fit for that cheap jewellery which is made of jet. Is there not at least that division into segments, which is the documentary proof of the insect? No! A pebble is not more lifeless.

Perhaps we shall find on the under surface [314]of the globule, in the part in contact with the twig, some trace of animal structure? The bead comes away easily and without breaking, like a berry. The base is slightly flattened and powdered with a white waxy substance which acts as a cement and causes the bead to adhere to the twig. Soaked in alcohol for twenty-four hours this substance dissolves and leaves uncovered the part to be examined.

Careful examination with the lens fails to reveal on the base of the bead the legs, or claws, however minute, which would serve to establish the fact of animal life. Nor does it reveal the sucker which, implanted in the bark, would imbibe the sap, that indispensable aliment. Although less smooth than the back, this portion is as bare as the rest. One would say, in fact, that the Kermes adheres to the twig because it is cemented to it, but has no other connection with it.

This cannot be the case. The black bead feeds itself; it grows; and without cessation it pours forth a product which might be the work of the distiller. To make up for such expenditure it must at least possess a rostrum to perforate the juicy bark. It assuredly [315]does possess such an organ, but so small that my worn eyes are powerless to detect it.

At the very moment of detaching the Kermes from its support the implement of suction may possibly withdraw itself, shrinking into itself to the point of becoming invisible.

In that half of the sphere which lies toward the base of the twig, the globule is traversed by a wide furrow which occupies the greater part of the half-meridian. At the lower edge of this furrow, on the confines of the supporting base, is a narrow opening, in the shape of a button-hole. By this opening only is the Kermes in touch with the outer world. It is a gate which serves many functions, and first of all, that of a fountain of syrup.

Let us cull a few twigs of evergreen oak peopled by Kermes and place the cut ends in a glass of water. The foliage will remain fresh for some time—a condition which will suffice to ensure the insects’ welfare. We shall see, ere long, a colourless, transparent fluid which, in the course of a couple of days, collects itself into a drop equal in volume to [316]the flask from which it oozes. If it becomes too heavy the drop falls, but without flowing over the Kermes, for the outlet is as it were a postern gate. Another drop at once begins to form. The spring is not intermittent, but perpetual; uninterrupted it sheds its solitary tears.

With the tip of the little finger let us gather this drop from the still and taste it. Delicious! In taste and aroma it is very nearly equal to honey. If the Kermes were to lend itself to wholesale rearing as well as to the easy harvesting of its product, we should have in it a valuable sugar-refiner. But it is for others to exploit it with the needful diligence and devotion.

These others are the Ants, those patient harvesters. They make for the Kermes even more eagerly than for the Plant-louse or Green-fly. The latter is niggardly in the matter of yielding its ambrosia; the Ant has to solicit it with patience; tickling its paunch before she can obtain even a meagre sip from the tips of its tiny horns. The Kermes is a spendthrift. Fully consenting, and at any moment, it permits all comers to [317]quench their thirst from its cellar, and its liquid largesse is offered in streams.

The Ants, therefore, crowd about the distillery; they form quite a company; by threes and fours they lick the opening of the gourd-like vessel; and however high the Kermes is installed amidst the foliage of the oak, they possess a most wonderful power of discovering it. When I see one slowly climbing I have only to follow her with my eyes; she takes me straight to the Ant’s tavern. She is my infallible guide when, still in its early youth, the Kermes by its minuteness would escape the glance of an eye not warned and on the alert. Even the very tiny insects are perambulating taverns and are well frequented like the big ones.

On the tree, in the full liberty of the fields, the diligence of the Ants, collecting the syrup as it oozes forth, will hardly permit us to estimate the value of the spring. The little round barrel, incessantly drained dry, shows barely a trace of moisture round the bung-hole. We must take an isolated twig, far from thirsty drinkers, to determine the true value of this flask of nectar. Then, in [318]the absence of the Ants, we see the liquor collecting with considerable rapidity in a drop of surprising volume. The extravasated fluid exceeds the capacity of the beaker, and the trickling continues, as evenly and abundantly as before. The sugar-refinery is now in permanent business; when there is no syrup left there is still plenty to come.

The Ants rear the Plant-lice, their milch-cows. What herds they would amass, what incalculable benefits they would derive therefrom, if the Kermes could only be reared in captivity! But it is found only in isolated groups, which, for that matter, are not numerous in themselves, and it cannot be moved from spot to spot. Removed from its position it dies, unable to take root elsewhere. The Ants exploit it where they find it, without the slightest effort to gather together a flock of Lice in a leafy chalet. Their ingenuity wisely draws back when confronted by the impossible.

What is the purpose of this nectar, so plentiful and so highly appreciated by the connoisseur? Can it be that it flows forth for the benefit of the Ants? After all, why not? In virtue of their number and their [319]activity as harvesters, they perform a function of far-reaching significance in the general picnic of living creatures. As the price of their services, they are granted the horn-shaped nectar of the Plant-louse and the fountain of the Kermes.

At the end of May let us break open the black capsule. Beneath the envelope, hard and brittle, a hasty dissection shows us eggs: nothing but eggs. We looked for the apparatus of a distiller of liqueurs, for rows of retorts; we find only an obtrusive ovary. The Kermes is little more than a coffer bursting with germs.

The germs are white, and assembled to the number of thirty or thereabouts, in little groups or clusters, which remind us, as regards their arrangement, of the masses of seeds in the buttercup. Tufts of extremely fine tracheal filaments encompass the glomeruli, surrounding them with an inextricable litter which makes an exact count impossible. A rough approximation gives us a hundred. The total of the eggs would therefore be some thousands.

What does the Kermes want with this prodigious number of offspring? An alchemist [320]of the general food supply, it does as do so many others among the humble creatures predestined to the elaboration of nutritive molecules: by means of excess numbers it seeks to avert the extermination with which it is threatened. With its liquor it provides the Ant, an importunate guest perhaps, but not a dangerous one, with a delicious beverage; on the other hand, with its eggs it nourishes a consumer who would lead to the extinction of the Kermes, were it not itself subjected to a drastic thinning out.

It has so happened that I have found the lover of omelettes at work. It is a negligible little grub which creeps from one tiny cluster to another, emptying his eggs still enclosed in their natal sheath. As a usual thing it is alone; sometimes it has companions—two, three or more. Ten, according to my notes, is the largest number recorded by its holes of exit.

How did it find its way into the strong-box, armoured on every side with impenetrable horn? We may be sure that it was introduced while yet a germ through the button-hole aperture whence oozes the syrup. A mother must have chanced this way, who, [321]discovering the orifice, took a sip, and then, turning herself about, plunged her oviduct into the opening. Here, without use of violence, the enemy entered the citadel.

The enemy belongs to the tribe of Chalcidians, those zealous ransackers of entrails. An extremely rapid worker, she acquires her adult form and emerges from the shell in the early part of June. In comparison with the offspring of the Kermes she is a giant, being no less than a twelfth part of an inch in length. The narrow dormer-window by which the germ was introduced being no longer able to give it passage, the recluse, with his patient, steely tooth, opens a door of emergence for himself through the wall of the shell, so that the latter is finally pierced with as many round openings as there were fellow-feasters. When they have departed the coffer is empty; there is no trace left of the plentiful omelette.

This ravager of ovaries is of a deep bluish-black colour; dark, concave wings, closely pressed down after the fashion of the elytral apron, giving it a vague look of the Beetle family. The head is flattened, projecting beyond the corselet on either side; [322]the powerful mandibles are such as are needed to perforate the tough, leathery wall. The long antennæ, incessantly vibrating, bent at an angle, slightly dilated at the tip, are ornamented with a white ring. Dumpy and thickset, the tiny creature runs swiftly along, polishing its wings and brushing its antennæ; it is full of delight at having emptied the belly of a Kermes. Has it a name in our scientific catalogue? I do not know, and am not especially anxious to know. A label in barbarous Latin would afford the reader no more information than would a few lines of history.

June is nearly over. For some time the sugary oozing has ceased; the Ants no longer come to their restaurant, a sign of profound alteration within. The outer aspect, however, has undergone no modification. We still have the small, black, glossy sphere, smooth and firmly fixed on its base, which is whitened with wax. With the point of a pen-knife let us break open the ebony casket, at the upper pole, at a point opposite the point of adhesion. Its wall is quite as hard and brittle as the wing-cover of a Scarabæus. Within, not a trace remains of the [323]juicy pulp: the contents consist of a dry meal, a mixture of red and white specks.

Let us collect this powder in a small glass tube; let us reinforce our sight by a magnifying-glass, and examine it. The appearance of the stuff is amazing. This dust is moving, these ashes are alive, and with life so numerous that the very idea of computation becomes alarming. It is the legion of the uncountable. In safeguarding a Louse fecundity knows no limits.

By their white hue we may distinguish those eggs that are not yet ripe for hatching. Now, at the end of June, these are the less numerous. The others, coloured by the tiny creatures within them, are bright red or orange yellow. Preponderant over all is the collection of white specks, the tattered husks of the eggs which have been hatched.

Now these discarded husks are arranged in radiating clusters, just as were the germs in the glomerulus of the ovary. This detail informs us that there was no period of egg-laying; that is, not only were the eggs not conveyed to a point external to the mother’s body, but they were not even conveyed to any particular point of the enclosure [324]bounded by the carapace, by a common protecting roof. They were hatched on the very site of their formation. The bunches of eggs, their arrangement and position remaining unchanged, have become clusters of offspring.

The Psyche has already provided an example of that singular genesis which exempts the mother from the process of egg-laying, the family being hatched out on the spot occupied by the eggs. Let us recall the shapeless moth, whose appearance is even more miserable than that of the caterpillar. She withdraws herself into the husk of her chrysalid, and there she wastes away, swollen with eggs which will be hatched on the spot. The mother Psyche becomes a lifeless bag whence emerges her living family. This is likewise the case of the Kermes.

I witness the process of birth. The new-born insects are struggling to escape from their envelopes. Many of them succeed in doing so by leaving the delicate husk of the egg where it is fastened, still included in the radiating pattern. Others, no less numerous, drag their sheath from its place and for a long time trail it after them, hanging [325]to their hinder parts. It adheres so firmly that the tiny creature is able to cross the threshold of the shell with its moulted husk, completing its liberation in the open air. Thus it is that we find on the natal twig, at some distance from the maternal pill, numbers of white discarded husks, which, if one had not closely followed the progress of events, would give one reason to believe that the eggs were hatched outside the Kermes. These filmy envelopes are deceptive; for the whole family was hatched inside the coffer.

Having collected the living dust with which it is now filled, let us glance at the ebony box itself. The cavity is divided into two storeys by a transverse partition, a fine-spun relic of the dessicated animal. The individual substance of the Kermes was so little that it is now represented by a delicate film. The rest of the mass enclosed by the shell appertains to the ovaries. The upper storey is therefore occupied by the newly born no less than the lower.

It is easy to emerge from this latter compartment when the time of the exodus has arrived; at its base is an ever-open door, [326]a fissure shaped like a button-hole. But how is it possible to escape from the upper storey, separated from the other as it is by a partition? The newly-hatched young are so feeble, so tiny, that they would never be able to break through the membrane. Let us look more closely. The partition is pierced in the centre by a round manhole! The inhabitants of the lower storey can make immediate use of the door of their dwelling-house, the button-hole exit; those of the upper storey can reach it by means of the hole in the floor. Magnificent foresight on the part of the mechanism of the dessication! The mother Kermes, of whom no more is left than an unsubstantial ceiling, contrives in her substance a trap-door without which half her family would die imprisoned.

Owing to its minute proportions, the tiny insect all but escapes the unaided eye. A good magnifying-glass shows it as a tiny Louse, shaped like an egg, the large end of the egg to the fore, and in colour a delicate reddish brown. It has six very active legs. Its motionless future, its lifeless maturity, are prefaced by a quick, toddling walk. The [327]long antennæ are in constant vibration; on the hinder part of the body are two long, diaphanous cirri, which will escape remark unless we look for them with sustained attention. There are two black eye-spots.

In the small glass test-tube in which I am observing it, the tiny creature appears to be extremely busy. It strays hither and thither, the antennæ outspread and waving to and fro; it climbs, descends, and climbs again, wandering this way and that, colliding as it goes with the torn skins of the hatched eggs. It is making ready for departure, that is evident. This mere speck of life is about to adventure into the wide world. What does it want? Apparently a sprig of its food plant. I have had an eye to its requirements.

In the orchard is an evergreen oak, one single specimen, a small but sturdy tree some ten to twelve feet in height. About the middle of June, when the young are beginning to appear, I place there some thirty Kermes, still adhering to their supporting twig.

In spite of all my pains, it will be no easy matter to follow the peregrinations of the Kermes’ family, should it disperse itself [328]over the tree, as I suppose it will. The traveller is too small and the country to be explored too vast. Moreover, to examine the tips of all the boughs with the magnifying-glass, leaf by leaf, twig by twig, is impracticable; no one’s patience would suffice to the task.

A few days later I inspect those that are within my range. Many migrations have taken place, as is proved by the white filmy skins left by the roadside. As for the young, I cannot see them anywhere, neither on the bark of the twigs, nor on the leaves. Is it possible that they have all attained the inaccessible tips of the boughs? Or can they have gone elsewhere? This is the first problem to be solved, and it must be solved under such conditions that the emigrants cannot escape my gaze.

I transplant some young evergreen oaks ten to twenty inches in height, into flowerpots filled with leaf-mould. On the twigs of each young tree I fix, with a little drop of gum, five or six Kermes, taking especial care not to obstruct the door of emergence. This miniature artificial coppice is placed where it is sheltered from the fiercest heat [329]of the sun, in my study, facing one of the windows.

On the 2nd of July I witness a migration. At the hottest time of the day, about two o’clock, the new-born Lice leave their fortress in an innumerable swarm. The young Kermes emerge hastily from the door of their dwelling, the button-hole-shaped cleft; many of them dragging behind them the discarded husk of the egg. For a moment they stand motionless on the domed roof of their spherical house; then they scatter over the neighbouring twigs. Several of them climb upwards and reach the summit of the plant, without appearing to gain much satisfaction from their ascent; some of them climb downwards along their twig, so that I cannot possibly guess what objective the swarm is seeking. It may be that we are witnessing a brief period of disorder, due to the joy of the first few steps in a world of unrestricted freedom; the tiny creatures may be wandering at random, abandoned to the delights of emancipation. Let them do as they will; they will soon quiet down.

On the following day, indeed, I can no longer see a single Louse on the tree; all [330]have found their way downwards to the black leaf-mould in the flowerpot, not far from the main stem. This mould, recently watered, is rich in the savours of foliage which has rotted and fallen into dust. There, on a surface barely larger than one’s fingernail, the little creatures have gathered into a closely packed flock. Not one of them moves, so well satisfied do they seem with their pasture, or rather their watering-place. As far as I can see they are feeding, motionless in their well-being.

I do what I can to increase their felicity. To keep the place cool and to provide a little shadow I cover it with a few dead leaves from the evergreen oak, previously moistened in a glass of water. And now, little Lice, you must proceed after your own fashion; I have done for you all that I can!

I have just learned of one essential point of your history, one detail, without which all the rest of my investigations must inevitably have come to naught. My first conjectures, although perfectly reasonable, were unfounded. Instead of settling down on some twig, as their mother did before them, the young Lice descend to the ground at the [331]foot of their natal tree. There, in the midst of the mosses and dead leaves, they find a shelter offering some degree of coolness, which will nourish them with its exudations, at all events at the outset.

And what do they live upon later?—I am not in a position to say. For five or six days I find them on the same spot, a motionless flock. Not one of them leaves the flock, not one of them descends underground. Then their numbers begin to diminish; little by little they all disappear, evaporating as it were, returning to that nothingness from which they were so little removed. The flock of atomies has left not a trace.

Apparently the flowerpot with its evergreen oak did not sufficiently fulfil the conditions of prosperity. There should have been also some grasses with underground rootstocks: in short, a jungle of herbaceous vegetation, rich in superficial root-fibres in which the young Kermes would have implanted their suckers. Is this the trouble?

I continue my investigations in the open country, at the foot of some evergreen oaks which, I noted, were thickly populated in May. The families of Lice are certainly [332]there, within a fairly small radius, for the puny little creatures are incapable of a lengthy journey. I inspect the varied vegetation covering the ground beneath the trees; I dig, uproot, and patiently, lens in hand, examine one by one the roots and stems grubbed up. Repeatedly resumed, in winter as well as in autumn, my laborious investigations are fruitless; the tiny Louse cannot be found.

The following year, on the return of spring, I was to learn that the presence of vegetation at the foot of the tree is not a necessity. Let us go back to the evergreen oak in the orchard. I peopled its foliage with some thirty Kermes which had reached maturity. There emerged from it, caravan by caravan, a multitude of Lice. Now, at the foot of this tree and all around it, for a distance of some yards, the soil is perfectly bare. Not a blade of grass, not a weed of any sort, has sprouted on this surface, so recently excavated by the spade. As for the roots of the oak itself, it is, as far as I can judge, useless to take them into account; for they lie at depths which the tiny Louse could never attain.[333]

Yet in May the tree, hitherto exempt from Kermes, is covered with black pills. My sowing has prospered; the young Lice which emerged from the shells have passed the winter underground, and on the advent of warm weather have returned to the tree, there to transform themselves into globules. What did they live on in this ungrateful soil, which contains not a single root-fibre? Probably on nothing at all.

They descend to earth in search of shelter rather than refreshment. Their refuge against the inclemencies of winter is precarious indeed, if it consists, as everything seems to declare, in a few cracks in some lump of earth, not far from the surface. In a hard winter, how many of these ill-protected creatures must disappear? To the ravages of the devourers of new-laid eggs we must add the more dreadful depredations of winter; and thus it is that in order to preserve one life the Kermes gives birth to thousands upon thousands.

The remainder of its story is not easily discovered. It is now the beginning of April. My three children, the joy of my declining years, lend me the keen sight of [334]youth. Without their assistance I should abandon all thought of the chase, which I now propose to pursue on the confines of invisibility. The previous year certain thickets of evergreen oak, well within the reach of the observer, were marked down as being thickly peopled by the Kermes. At that time I marked every populated twig with a white thread.

It is here that my little collaborators patiently pursue their investigations, leaf by leaf, and twig by twig. After a brief glimpse through my lens the harvest is placed in a botanist’s specimen box; a more scrupulous examination will be made in my study, with all the conveniences which the observer may require.

On the seventh of April, just as I am beginning to despair of my investigations, the tiny insect crosses the field of my pocket microscope. This is she, actually this is she! Just as I saw her last year emerging from her natal shell, so once more I behold her now. No change whatever is visible: neither of aspect, nor shape, nor colouration, nor size. She goes bustling along as though [335]busy in the extreme, searching doubtless for a spot to her liking. At every moment the smallest wrinkle in the bark conceals her from sight. I place the twig that bears the precious atomy under a bell-glass. On the following day I expect a moult. The bustling little insect is replaced by a motionless corpuscle. This is the first stage of the globular Kermes. Fortune has only once vouchsafed me such a “find,” which would have been examined in greater detail had I possessed a sufficient number of subjects. My inspection of the evergreen oaks was somewhat in arrears; I ought to have made it in March. At this period, I imagine, I should have caught the insect emerging from the soil and returning to the foliage of its oak-tree, in order there to undergo transformation. Instead of one single subject I should have had many, though even then I could not have counted upon a numerous collection, for the hardships of winter have certainly thinned out those families, which were in the beginning so numerous. They descended from the tree in their hundreds of thousands; they [336]climb it again in scanty groups, as is attested by the scarcity of the black globules in the warm weather.

As for what becomes of the climbers, my single specimen tells us plainly enough. It has become a spherical speck, the indubitable sign of the future Kermes. In a few days’ time it has dried up, despite the glass of water into which the base of the twig was immersed. Fortunately I have a few other similar corpuscles, a little more developed. My gleanings give me two kinds of corpuscle.

The more numerous are spherical in shape, their size varying according to their age. The smallest are rarely a millimetre2 in diameter. The ventral surface is flat, and surrounded by a snowy cushion, the rough foundation of the waxy base. The dorsal surface is rounded, and in colour of a rusty red or pale chestnut with delicate white tufts distributed without any orderly arrangement. In this costume the young Kermes reminds us of a certain shell found in tropical seas: the striped or tiger cowry. The sugar refinery is already at work. At the back of the shell a limpid drop is gathering, to [337]which the Ants repair in order to quench their thirst. In a few weeks’ time the colour has changed to an ebony black, the sphere has attained the size of a pea and the Kermes has reached its final state.

The minority stretch themselves out in the likeness of a tiny half-contracted slug. The ventral surface is flat and its whole area is closely applied to the twig. The dorsal surface is convex, and its colour a more or less vivid amber yellow. It is sprinkled with protuberant specks of a snowy white, arranged in longitudinal rows to the number of five or seven. With its amber yellow colouration and its ornamentation of white specks, the tiny creature has something of the look of a certain kind of pastry which is sprinkled with spots of white sugar. There is no oozing of a syrupy liquid to the rear of the insect, so that the Ants do not visit it.

I have conjectured that this second form is the larval state of the males. From this, I imagine, will emerge winged insects ready for mating. To verify this guess of mine is impossible. My slug-like specimens die on their withering twig, and to follow their development beyond the walls of my study [338]would be an undertaking too great for my patience.

Of this very incomplete history of the Kermes of the oak-tree, one point especially should be remembered. The mother, an enormous ovary, exempt from the labours of egg-laying, contracts into a strong-box in which the family is hatched without the removal of the eggs. Within this shrivelled relic the family swarms in its thousands until the moment of exodus. Simplifying to the very extreme the usual method of procreation, the insect turns into a boxful of young.