Let us create a disturbance among the globular group by stirring it with a straw. All wake up at once. The cluster softly dilates and spreads, as though set in motion by some centrifugal force; it becomes a transparent orb wherein thousands and thousands of tiny legs quiver and shake, while threads are extended along the way to be followed. The whole work resolves itself into a delicate veil which swallows up the scattered family. We then see an exquisite nebula against whose opalescent tapestry the tiny animals gleam like twinkling orange stars.
This straggling state, though it last for hours, is but temporary. If the air grow cooler, if rain threaten, the spherical group reforms at once. This is a protective measure. On the morning after a shower, I find the families on either bamboo in as good condition as on the day before. The silk veil and the pill formation have sheltered them well enough from the downpour. Even so do Sheep, when caught in a storm in the pastures, gather close, huddle together and make a common rampart of their backs.
The assembly into a ball-shaped mass is also the rule in calm, bright weather, after the morning's exertions. In the afternoon, the climbers collect at a higher point, where they weave a wide, conical tent, with the end of a shoot for its top, and, gathered into a compact group, spend the night there. Next day, when the heat returns, the ascent is resumed in long files, following the shrouds which a few pioneers have rigged and which those who come after elaborate with their own work.
Collected nightly into a globular troop and sheltered under a fresh tent, for three or four days, each morning, before the sun grows too hot, my little emigrants thus raise themselves, stage by stage, on both bamboos, until they reach the sun-unit, at fifteen feet above the ground. The climb comes to an end for lack of foothold.
Under normal conditions, the ascent would be shorter. The young Spiders have at their disposal the bushes, the brushwood, providing supports on every side for the threads wafted hither and thither by the eddying air- currents. With these rope-bridges flung across space, the dispersal presents no difficulties. Each emigrant leaves at his own good time and travels as suits him best.
My devices have changed these conditions somewhat. My two bristling poles stand at a distance from the surrounding shrubs, especially the one which I planted in the middle of the yard. Bridges are out of the question, for the threads flung into the air are not long enough. And so the acrobats, eager to get away, keep on climbing, never come down again, are impelled to seek in a higher position what they have failed to find in a lower. The top of my two bamboos probably fails to represent the limit of what my keen climbers are capable of achieving.
We shall see, in a moment, the object of this climbing-propensity, which is a sufficiently remarkable instinct in the Garden Spiders, who have as their domain the low-growing brushwood wherein their nets are spread; it becomes a still more remarkable instinct in the Lycosa, who, except at the moment when she leaves her mother's back, never quits the ground and yet, in the early hours of her life, shows herself as ardent a wooer of high places as the young Garden Spiders.
Let us consider the Lycosa in particular. In her, at the moment of the exodus, a sudden instinct arises, to disappear, as promptly and for ever, a few hours later. This is the climbing-instinct, which is unknown to the adult and soon forgotten by the emancipated youngling, doomed to wander homeless, for many a long day, upon the ground. Neither of them dreams of climbing to the top of a grass-stalk. The full-grown Spider hunts trapper-fashion, ambushed in her tower; the young one hunts afoot through the scrubby grass. In both cases there is no web and therefore no need for lofty contact-points. They are not allowed to quit the ground and climb the heights.
Yet here we have the young Lycosa, wishing to leave the maternal abode and to travel far afield by the easiest and swiftest methods, suddenly becoming an enthusiastic climber. Impetuously she scales the wire trellis of the cage where she was born; hurriedly she clambers to the top of the tall mast which I have prepared for her. In the same way, she would make for the summit of the bushes in her waste-land.
We catch a glimpse of her object. From on high, finding a wide space beneath her, she sends a thread floating. It is caught by the wind and carries her hanging to it. We have our aeroplanes; she too possesses her flying-machine. Once the journey is accomplished, naught remains of this ingenious business. The climbing-instinct conies suddenly, at the hour of need, and no less suddenly vanishes.
CHAPTER VII: THE SPIDERS' 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, {28} 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.