The Spider's Exodus
Seeds, when ripened in the fruit, are disseminated, that is to say, scattered on the surface of the ground, to sprout in spots as yet unoccupied and fill the expanses that realize favourable conditions.
Amid the wayside rubbish grows one of the gourd family, Ecbalium elaterium, commonly called the squirting cucumber, whose fruit—a rough and extremely bitter little cucumber—is the size of a date. When ripe, the fleshy core resolves into a liquid in which float the seeds. Compressed by the elastic rind of the fruit, this liquid bears upon the base of the footstalk, which is gradually forced out, yields like a stopper, breaks off and leaves an orifice through which a stream of seeds and fluid pulp is suddenly ejected. If, with a novice hand, under a scorching sun, you shake the plant laden with yellow fruit, you are bound to be somewhat startled when you hear a noise among the leaves and receive the cucumber's grapeshot in your face.
The fruit of the garden balsam, when ripe, splits, at the least touch, into five fleshy valves, which curl up and shoot their seeds to a distance. The botanical name of Impatiens given to the balsam alludes to this sudden dehiscence of the capsules, which cannot endure contact without bursting.
In the damp and shady places of the woods there exists a plant of the same family which, for similar reasons, bears the even more expressive name of Impatiens noli-me-tangere, or touch-me-not.
The capsule of the pansy expands into three valves, each scooped out like a boat and laden in the middle with two rows of seeds. When these valves dry, the edges shrivel, press upon the grains and eject them.
Light seeds, especially those of the order of Compositae, have aeronautic apparatus—tufts, plumes, fly-wheels—which keep them up in the air and enable them to take distant voyages. In this way, at the least breath, the seeds of the dandelion, surmounted by a tuft of feathers, fly from their dry receptacle and waft gently in the air.
Next to the tuft, the wing is the most satisfactory contrivance for dissemination by wind. Thanks to their membranous edge, which gives them the appearance of thin scales, the seeds of the yellow wall-flower reach high cornices of buildings, clefts of inaccessible rocks, crannies in old walls, and sprout in the remnant of mould bequeathed by the mosses that were there before them.
The samaras, or keys, of the elm, formed of a broad, light fan with the seed cased in its centre; those of the maple, joined in pairs and resembling the unfurled wings of a bird; those of the ash, carved like the blade of an oar, perform the most distant journeys when driven before the storm.
Like the plant, the insect also sometimes possesses travelling-apparatus, means of dissemination that allow large families to disperse quickly over the country, so that each member may have his place in the sun without injuring his neighbour; and these apparatus, these methods vie in ingenuity with the elm's samara, the dandelion-plume and the catapult of the squirting cucumber.
Let us consider, in particular, the Epeirae, those magnificent Spiders who, to catch their prey, stretch, between one bush and the next, great vertical sheets of meshes, resembling those of the fowler. The most remarkable in my district is the Banded Epeira (Epeira fasciata, WALCK.), so prettily belted with yellow, black and silvery white. Her nest, a marvel of gracefulness, is a satin bag, shaped like a tiny pear. Its neck ends in a concave mouthpiece closed with a lid, also of satin. Brown ribbons, in fanciful meridian waves, adorn the object from pole to pole.
Open the nest. We have seen, in an earlier chapter, what we find there; let us retell the story. Under the outer wrapper, which is as stout as our woven stuffs and, moreover, perfectly waterproof, is a russet eiderdown of exquisite delicacy, a silky fluff resembling driven smoke. Nowhere does mother-love prepare a softer bed.
In the middle of this downy mass hangs a fine, silk, thimble-shaped purse, closed with a movable lid. This contains the eggs, of a pretty orange-yellow and about five hundred in number.
All things considered, is not this charming edifice an animal fruit, a germ-casket, a capsule to be compared with that of the plants? Only, the Epeira's wallet, instead of seeds, holds eggs. The difference is more apparent than real, for egg and grain are one.
How will this living fruit, ripening in the heat beloved of the Cicadae, manage to burst? How, above all, will dissemination take place? They are there in their hundreds. They must separate, go far away, isolate themselves in a spot where there is not too much fear of competition among neighbours. How will they set to work to achieve this distant exodus, weaklings that they are, taking such very tiny steps?
I receive the first answer from another and much earlier Epeira, whose family I find, at the beginning of May, on a yucca in the enclosure. The plant blossomed last year. The branching flower-stem, some three feet high, still stands erect, though withered. On the green leaves, shaped like a sword-blade, swarm two newly-hatched families. The wee beasties are a dull yellow, with a triangular black patch upon their stern. Later on, three white crosses, ornamenting the back, will tell me that my find corresponds with the Cross or Diadem Spider (Epeira diadema, WALCK.).
When the sun reaches this part of the enclosure, one of the two groups falls into a great state of flutter. Nimble acrobats that they are, the little Spiders scramble up, one after the other, and reach the top of the stem. Here, marches and countermarches, tumult and confusion reign, for there is a slight breeze which throws the troop into disorder. I see no connected manoeuvres. From the top of the stalk they set out at every moment, one by one; they dart off suddenly; they fly away, so to speak. It is as though they had the wings of a Gnat.
Forthwith they disappear from view. Nothing that my eyes can see explains this strange flight; for precise observation is impossible amid the disturbing influences out of doors. What is wanted is a peaceful atmosphere and the quiet of my study.
I gather the family in a large box, which I close at once, and instal it in the animals' laboratory, on a small table, two steps from the open window. Apprised by what I have just seen of their propensity to resort to the heights, I give my subjects a bundle of twigs, eighteen inches tall, as a climbing-pole. The whole band hurriedly clambers up and reaches the top. In a few moments there is not one lacking in the group on high. The future will tell us the reason of this assemblage on the projecting tips of the twigs.
The little Spiders are now spinning here and there at random: they go up, go down, come up again. Thus is woven a light veil of divergent threads, a many-cornered web with the end of the branch for its summit and the edge of the table for its base, some eighteen inches wide. This veil is the drill-ground, the work-yard where the preparations for departure are made.
Here hasten the humble little creatures, running indefatigably to and fro. When the sun shines upon them, they become gleaming specks and form upon the milky background of the veil a sort of constellation, a reflex of those remote points in the sky where the telescope shows us endless galaxies of stars. The immeasurably small and the immeasurably large are alike in appearance. It is all a matter of distance.
But the living nebula is not composed of fixed stars; on the contrary, its specks are in continual movement. The young Spiders never cease shifting their position on the web. Many let themselves drop, hanging by a length of thread, which the faller's weight draws from the spinnerets. Then quickly they climb up again by the same thread, which they wind gradually into a skein and lengthen by successive falls. Others confine themselves to running about the web and also give me the impression of working at a bundle of ropes.
The thread, as a matter of fact, does not flow from the spinneret; it is drawn thence with a certain effort. It is a case of extraction, not emission. To obtain her slender cord, the Spider has to move about and haul, either by falling or by walking, even as the rope-maker steps backwards when working his hemp. The activity now displayed on the drill-ground is a preparation for the approaching dispersal. The travellers are packing up.
Soon we see a few Spiders trotting briskly between the table and the open window. They are running in mid-air. But on what? If the light fall favourably, I manage to see, at moments, behind the tiny animal, a thread resembling a ray of light, which appears for an instant, gleams and disappears. Behind, therefore, there is a mooring, only just perceptible, if you look very carefully; but, in front, towards the window, there is nothing to be seen at all.
In vain I examine above, below, at the side; in vain I vary the direction of the eye: I can distinguish no support for the little creature to walk upon. One would think that the beastie were paddling in space. It suggests the idea of a small bird, tied by the leg with a thread and making a flying rush forwards.
But, in this case, appearances are deceptive: flight is impossible; the Spider must necessarily have a bridge whereby to cross the intervening space. This bridge, which I cannot see, I can at least destroy. I cleave the air with a ruler in front of the Spider making for the window. That is quite enough: the tiny animal at once ceases to go forward and falls. The invisible foot-plank is broken. My son, young Paul, who is helping me, is astounded at this wave of the magic wand, for not even he, with his fresh, young eyes, is able to see a support ahead for the Spiderling to move along.
In the rear, on the other hand, a thread is visible. The difference is easily explained. Every Spider, as she goes, at the same time spins a safety-cord which will guard the rope-walker against the risk of an always possible fall. In the rear, therefore, the thread is of double thickness and can be seen, whereas, in front, it is still single and hardly perceptible to the eye.
Obviously, this invisible foot-bridge is not flung out by the animal: it is carried and unrolled by a gust of air. The Epeira, supplied with this line, lets it float freely; and the wind, however softly blowing, bears it along and unwinds it. Even so is the smoke from the bowl of a pipe whirled up in the air.
This floating thread has but to touch any object in the neighbourhood and it will remain fixed to it. The suspension-bridge is thrown; and the Spider can set out. The South-American Indians are said to cross the abysses of the Cordilleras in travelling-cradles made of twisted creepers; the little Spider passes through space on the invisible and the imponderable.
But to carry the end of the floating thread elsewhither a draught is needed. At this moment, the draught exists between the door of my study and the window, both of which are open. It is so slight that I do not feel its; I only know of it by the smoke from my pipe, curling softly in that direction. Cold air enters from without through the door; warm air escapes from the room through the window. This is the drought that carries the threads with it and enables the Spiders to embark upon their journey.
I get rid of it by closing both apertures and I break off any communication by passing my ruler between the window and the table. Henceforth, in the motionless atmosphere, there are no departures. The current of air is missing, the skeins are not unwound and migration becomes impossible.
It is soon resumed, but in a direction whereof I never dreamt. The hot sun is beating on a certain part of the floor. At this spot, which is warmer than the rest, a column of lighter, ascending air is generated. If this column catch the threads, my Spiders ought to rise to the ceiling of the room.
The curious ascent does, in fact, take place. Unfortunately, my troop, which has been greatly reduced by the number of departures through the window, does not lend itself to prolonged experiment. We must begin again.
The next morning, on the same yucca, I gather the second family, as numerous as the first. Yesterday's preparations are repeated. My legion of Spiders first weaves a divergent framework between the top of the brushwood placed at the emigrants' disposal and the edge of the table. Five or six hundred wee beasties swarm all over this work-yard.
While this little world is busily fussing, making its arrangements for departure, I make my own. Every aperture in the room is closed, so as to obtain as calm an atmosphere as possible. A small chafing-dish is lit at the foot of the table. My hands cannot feel the heat of it at the level of the web whereon my Spiders are weaving. This is the very modest fire which, with its column of rising air, shall unwind the threads and carry them on high.
Let us first enquire the direction and strength of the current. Dandelion-plumes, made lighter by the removal of their seeds, serve as my guides. Released above the chafing-dish, on the level of the table, they float slowly upwards and, for the most part, reach the ceiling. The emigrants' lines should rise in the same way and even better.
The thing is done: with the aid of nothing that is visible to the three of us looking on, a Spider makes her ascent. She ambles with her eight legs through the air; she mounts, gently swaying. The others, in ever-increasing numbers, follow, sometimes by different roads, sometimes by the same road. Any one who did not possess the secret would stand amazed at this magic ascent without a ladder. In a few minutes, most of them are up, clinging to the ceiling.
Not all of them reach it. I see some who, on attaining a certain height, cease to go up and even lose ground, although moving their legs forward with all the nimbleness of which they are capable. The more they struggle upwards, the faster they come down. This drifting, which neutralizes the distance covered and even converts it into a retrogression, is easily explained.
The thread has not reached the platform; it floats, it is fixed only at the lower end. As long as it is of a fair length, it is able, although moving, to bear the minute animal's weight. But, as the Spider climbs, the float becomes shorter in proportion; and the time comes when a balance is struck between the ascensional force of the thread and the weight carried. Then the beastie remains stationary, although continuing to climb.
Presently, the weight becomes too much for the shorter and shorter float; and the Spider slips down, in spite of her persistent, forward striving. She is at last brought back to the branch by the falling threads. Here, the ascent is soon renewed, either on a fresh thread, if the supply of silk be not yet exhausted, or on a strange thread, the work, of those who have gone before.
As a rule, the ceiling is reached. It is twelve feet high. The little Spider is able, therefore, as the first product of her spinning-mill, before taking any refreshment, to obtain a line fully twelve feet in length. And all this, the rope-maker and her rope, was contained in the egg, a particle of no size at all. To what a degree of fineness can the silky matter be wrought wherewith the young Spider is provided! Our manufacturers are able to turn out platinum-wire that can only be seen when it is made red-hot. With much simpler means, the Spiderling draws from her wire-mill threads so delicate that, even the brilliant light of the sun does not always enable us to discern them.
We must not let all the climbers be stranded on the ceiling, an inhospitable region where most of them will doubtless perish, being unable to produce a second thread before they have had a meal. I open the window. A current of lukewarm air, coming from the chafing-dish, escapes through the top. Dandelion-plumes, taking that direction, tell me so. The wafting threads cannot fail to be carried by this flow of air and to lengthen out in the open, where a light breeze is blowing.
I take a pair of sharp scissors and, without shaking the threads, cut a few that are just visible at the base, where they are thickened with an added strand. The result of this operation is marvellous. Hanging to the flying-rope, which is borne on the wind outside, the Spider passes through the window, suddenly flies off and disappears. An easy way of travelling, if the conveyance possessed a rudder that allowed the passenger to land where he pleases! But the little things are at the mercy of the winds: where will they alight? Hundreds, thousands of yards away, perhaps. Let us wish them a prosperous journey.
The problem of dissemination is now solved. What would happen if matters, instead of being brought about by my wiles, took place in the open fields? The answer is obvious. The young Spiders, born acrobats and rope-walkers, climb to the top of a branch so as to find sufficient space below them to unfurl their apparatus. Here, each draws from her rope-factory a thread which she abandons to the eddies of the air. Gently raised by the currents that ascend from the ground warmed by the sun, this thread wafts upwards, floats, undulates, makes for its point of contact. At last, it breaks and vanishes in the distance, carrying the spinstress hanging to it.
The Epeira with the three white crosses, the Spider who has supplied us with these first data concerning the process of dissemination, is endowed with a moderate maternal industry. As a receptacle for the eggs, she weaves a mere pill of silk. Her work is modest indeed beside the Banded Epeira's balloons. I looked to these to supply me with fuller documents. I had laid up a store by rearing some mothers during the autumn. So that nothing of importance might escape me, I divided my stock of balloons, most of which were woven before my eyes, into two sections. One half remained in my study, under a wire-gauze cover, with, small bunches of brushwood as supports; the other half were experiencing the vicissitudes of open-air life on the rosemaries in the enclosure.
These preparations, which promised so well, did not provide me with the sight which I expected, namely, a magnificent exodus, worthy of the tabernacle occupied. However, a few results, not devoid of interest, are to be noted. Let us state them briefly.
The hatching takes place as March approaches. When this time comes, let us open the Banded Epeira's nest with the scissors. We shall find that some of the youngsters have already left the central chamber and scattered over the surrounding eiderdown, while the rest of the laying still consists of a compact mass of orange eggs. The appearance of the younglings is not simultaneous; it takes place with intermissions and may last a couple of weeks.
Nothing as yet suggests the future, richly-striped livery. The abdomen is white and, as it were, floury in the front half; in the other half it is a blackish-brown. The rest of the body is pale-yellow, except in front, where the eyes form a black edging. When left alone, the little ones remain motionless in the soft, russet swan's-down; if disturbed, they shuffle lazily where they are, or even walk about in a hesitating and unsteady fashion. One can see that they have to ripen before venturing outside.
Maturity is achieved in the exquisite floss that surrounds the natal chamber and fills out the balloon. This is the waiting-room in which the body hardens. All dive into it as and when they emerge from the central keg. They will not leave it until four months later, when the midsummer heats have come.
Their number is considerable. A patient and careful census gives me nearly six hundred. And all this comes out of a purse no larger than a pea. By what miracle is there room for such a family? How do those thousands of legs manage to grow without straining themselves?
The egg-bag, as we learnt in Chapter II., is a short cylinder rounded at the bottom. It is formed of compact white satin, an insuperable barrier. It opens into a round orifice wherein is bedded a lid of the same material, through which the feeble beasties would be incapable of passing. It is not a porous felt, but a fabric as tough as that of the sack. Then by what mechanism is the delivery effected?
Observe that the disk of the lid doubles back into a short fold, which edges into the orifice of the bag. In the same way, the lid of a saucepan fits the mouth by means of a projecting rim, with this difference, that the rim is not attached to the saucepan, whereas, in the Epeira's work, it is soldered to the bag or nest. Well, at the time of the hatching, this disk becomes unstuck, lifts and allows the new-born Spiders to pass through.
If the rim were movable and simply inserted, if, moreover, the birth of all the family took place at the same time, we might think that the door is forced open by the living wave of inmates, who would set their backs to it with a common effort. We should find an approximate image in the case of the saucepan, whose lid is raised by the boiling of its contents. But the fabric of the cover is one with the fabric of the bag, the two are closely welded; besides, the hatching is effected in small batches, incapable of the least exertion. There must, therefore, be a spontaneous bursting, or dehiscence, independent of the assistance of the youngsters and similar to that of the seed-pods of plants.
When fully ripened, the dry fruit of the snap-dragon opens three windows; that of the pimpernel splits into two rounded halves, something like those of the outer case of a fob-watch; the fruit of the carnation partly unseals its valves and opens at the top into a star-shaped hatch. Each seed-casket has its own system of locks, which are made to work smoothly by the mere kiss of the sun.
Well, that other dry fruit, the Banded Epeira's germ-box, likewise possesses its bursting-gear. As long as the eggs remain unhatched, the door, solidly fixed in its frame, holds good; as soon as the little ones swarm and want to get out, it opens of itself.
Come June and July, beloved of the Cicadae, no less beloved of the young Spiders who are anxious to be off. It were difficult indeed for them to work their way through the thick shell of the balloon. For the second time, a spontaneous dehiscence seems called for. Where will it be effected?
The idea occurs off-hand that it will take place along the edges of the top cover. Remember the details given in an earlier chapter. The neck of the balloon ends in a wide crater, which is closed by a ceiling dug out cup-wise. The material is as stout in this part as in any other; but, as the lid was the finishing touch to the work, we expect to find an incomplete soldering, which would allow it to be unfastened.
The method of construction deceives us: the ceiling is immovable; at no season can my forceps manage to extract it, without destroying the building from top to bottom. The dehiscence takes place elsewhere, at some point on the sides. Nothing informs us, nothing suggests to us that it will occur at one place rather than another.
Moreover, to tell the truth, it is not a dehiscence prepared by means of some dainty piece of mechanism; it is a very irregular tear. Somewhat sharply, under the fierce heat of the sun, the satin bursts like the rind of an over-ripe pomegranate. Judging by the result, we think of the expansion of the air inside, which, heated by the sun, causes this rupture. The signs of pressure from within are manifest: the tatters of the torn fabric are turned outwards; also, a wisp of the russet eiderdown that fills the wallet invariably straggles through the breach. In the midst of the protruding floss, the Spiderlings, expelled from their home by the explosion, are in frantic commotion.
The balloons of the Banded Epeira are bombs which, to free their contents, burst under the rays of a torrid sun. To break they need the fiery heat-waves of the dog-days. When kept in the moderate atmosphere of my study, most of them do not open and the emergence of the young does not take place, unless I myself I have a hand in the business; a few others open with a round hole, a hole so neat that it might have been made with a punch. This aperture is the work of the prisoners, who, relieving one another in turns, have, with a patient tooth, bitten through the stuff of the jar at some point or other.
When exposed to the full force of the sun, however, on the rosemaries in the enclosure, the balloons burst and shoot forth a ruddy flood of floss and tiny animals. That is how things occur in the free sun-bath of the fields. Unsheltered, among the bushes, the wallet of the Banded Epeira, when the July heat arrives, splits under the effort of the inner air. The delivery is effected by an explosion of the dwelling.
A very small part of the family are expelled with the flow of tawny floss; the vast majority remain in the bag, which is ripped open, but still bulges with eiderdown. Now that the breach is made, any one can go out who pleases, in his own good time, without hurrying. Besides, a solemn action has to be performed before the emigration. The animal must cast its skin; and the moult is an event that does not fall on the same date for all. The evacuation of the place, therefore, lasts several days. It is effected in small squads, as the slough is flung aside.
Those who sally forth climb up the neighbouring twigs and there, in the full heat of the sun, proceed with the work of dissemination. The method is the same as that which we saw in the case of the Cross Spider. The spinnerets abandon to the breeze a thread that floats, breaks and flies away, carrying the rope-maker with it. The number of starters on any one morning is so small as to rob the spectacle of the greater part of its interest. The scene lacks animation because of the absence of a crowd.
To my intense disappointment, the Silky Epeira does not either indulge in a tumultuous and dashing exodus. Let me remind you of her handiwork, the handsomest of the maternal wallets, next to the Banded Epeira's. It is an obtuse conoid, closed with a star-shaped disk. It is made of a stouter and especially a thicker material than the Banded Epeira's balloon, for which reason a spontaneous rupture becomes more necessary than ever.
This rupture is effected at the sides of the bag, not far from the edge of the lid. Like the ripping of the balloon, it requires the rough aid of the heat of July. Its mechanism also seems to work by the expansion of the heated air, for we again see a partial emission of the silky floss that fills the pouch.
The exit of the family is performed in a single group and, this time, before the moult, perhaps for lack of the space necessary for the delicate casting of the skin. The conical bag falls far short of the balloon in size; those packed within would sprain their legs in extracting them from their sheaths. The family, therefore, emerges in a body and settles on a sprig hard by.
This is a temporary camping-ground, where, spinning in unison, the youngsters soon weave an open-work tent, the abode of a week, or thereabouts. The moult is effected in this lounge of intersecting threads. The sloughed skins form a heap at the bottom of the dwelling; on the trapezes above, the flaylings take exercise and gain strength and vigour. Finally, when maturity is attained, they set out, now these, now those, little by little and always cautiously. There are no audacious flights on the thready airship; the journey is accomplished by modest stages.
Hanging to her thread, the Spider lets herself drop straight down, to a depth of nine or ten inches. A breath of air sets her swinging like a pendulum, sometimes drives her against a neighbouring branch. This is a step towards the dispersal. At the point reached, there is a fresh fall, followed by a fresh pendulous swing that lands her a little farther afield. Thus, in short tacks, for the thread is never very long, does the Spiderling go about, seeing the country, until she comes to a place that suits her. Should the wind blow at all hard, the voyage is cut short: the cable of the pendulum breaks and the beastie is carried for some distance on its cord.
To sum up, although, on the whole, the tactics of the exodus remain much the same, the two spinstresses of my region best-versed in the art of weaving mothers' wallets failed to come up to my expectations. I went to the trouble of rearing them, with disappointing results. Where shall I find again the wonderful spectacle which the Cross Spider offered me by chance? I shall find it—in an even more striking fashion—among humbler Spiders, whom I had neglected to observe.