Last Leaves from Dunk Island, by E. J. Banfield

Part III

A Spinner of Sand

Human knowledge will be struck off the world’s records before we know all that is to be said about a gnat. — FABRE.

When the smoke of the belated steamer was a mere smudge in still air far to the south-west, and there was naught to do but to wait for tidings, good or bad, from the sick and discomforted world — the din of which actually reaches these placid scenes — was it not meet to study the sand, a field of intense though noiseless industry, of edifying determination, of competitive forces working undesignedly to a common purpose, of exemplary utility?

In treacherous dimples the ferocious ant-lion, with mandibles one-third the length of its body, lies in wait for its prey — no king of the beasts more alert or more sudden or sure. Let a wandering ant venture beyond the verge of the trap, and the loose, fine sand slips under its tread; it slides to the bottom of the pit; there is a heave of the sand, and the ant disappears. But ants and their enemies are not the only intelligences in the raw sand. If that plume of smoke the steamer wears but keeps its distance, another and more primitive creature may make itself known.

If you believe that Nature’s restorative operations are performed unceasingly, with never-failing design and often with the exhibition of wonderful power, you may not be altogether astounded at the antics of seemingly inanimate things. On this flat a year ago was a thick sward of grass, perpetually mulched by millions of needles from the beach oaks. The cyclone buried both the grass and the mulching, so that the new surface was unprotected from shifting winds. To encourage the growth of plant-life retentive of sand, Nature employs certain advance agents, the successive office of each of which is to create ever so meagre an amelioration of the harsh conditions. Behold how one of these agents works.

Ordinarily the fallen needle — or branchlet — of a beach oak (CASUARINA EQUISETIFOLIA) is absolutely passive. Like the tree of the Bible, “In the place that it falleth there shall it be.” But here is one with its terminal spike of withered flowers that moves, though lacking apparent impulse, with a succession of jerks. It may be ten inches long, light of course, yet unaccountably mysterious in its actions. The terminal plume lifts and sways, as if some unfortunate creature were semaphoring signals of distress. May these dry things live and brave the light of day with frolicsome waverings?

Look at the other end, and for a moment the mystery deepens. It is slowly settling upright in the sand. Was ever conjurer’s trick more entertaining! Take hold of the plume; you will find a weak resistance to the strain you exert, and then the needle may be withdrawn. Let it lie for a moment, and again it apparently becomes invested with life. The plume lifts from the sand, wavers, and begins to heave itself upright, the frequent pauses in the operation proving that the task is a mighty one, demanding rests. Carry investigations a trifle further, and you will discover a sand-coloured grub, a trifle more robust of figure than the needle, holding the end with mandibles backed by definite purpose. Not one-tenth the length of the needle, the insect exerts almost magical strength, and is, moreover, endowed with determination to obey the dictates of Nature. Though apparently disliking exposure to the sunlight, yet, should the needle be withdrawn from its grip, the insect after an interval slowly and cautiously emerges, hastens to it, drags it once more to the entrance of its shaft, and withdraws, the waving plume registering each tug.

It is as if a six-foot man were to take hold of a flagstaff about a third the circumference of his own body and ten times his length, and retreat into the sand, dragging the staff with him. There is a circumstance, however, in favour of the herculean grub. Its shaft has been dug beforehand, though the entrance closes automatically and is not discoverable on the surface; further, it has a casing of web, reinforced with minute grains of sand. The shaft may be traced down six and eight inches. When you look about, you will find similar operations in progress by the dozen over every square yard of the sandy area. Indeed, in some places the casings of the shafts are so close together that there may be three or four in the space of a square inch. Some occupants are working on needles, or portions thereof, three and four inches long. The higher-minded grubs, those that tend to improve the conditions of the multitude, try to get ten-inch needles down eight-inch shafts, and not only try but succeed; for do they not nibble away the superfluous length, and as they nibble does not the plume tell of gigantic concentration of effort, crowned with the flourish of success? Thus do these sober-tinted, scarcely discernible grubs check the mobility of sand and make loam upon which plants may feed and be vigorous!

On the brief and hasty excursions of the insect above ground in search of food in the bulk, the mouth of the shaft closes automatically, as if controlled by a sphincter muscle. It seems quite safe to conjecture that it lays an invisible thread of gossamer thence as far as its quest lies, and that it is provided with terminal appendages for the opening of the entrance; for, on seizing the end of a needle, it retreats, with never a glance behind, as briskly as it advanced and with unhesitating precision to the spot whence it emerged. Tail first it descends; the mouth of the shaft closes round the needle, which gradually disappears, leaving not a trace.

By carefully clawing the sand a section of a shaft may be exposed, the casing being so frail that it falls away on the vertical face. The thrifty creature may have stored as many as twelve pieces of its food, varying in length from a quarter of an inch to an inch and a half. Here it is revealed, bolt upright, and so preoccupied with its nibbling that it does not on the instant seem to be aware of the disturbance of its quarters. When it does, it slightly curves itself and becomes passive. The bottom of the shaft is distended into a pocket by the weight of accumulated pellets of excrement. In some cases the quantity is about half a thimbleful. However alluring it may be to elaborate this point, with Darwin’s classic chronicles of the operations of earth-worms in mind, any such attempt would savour of parody. It would appear that the office of the tender caterpillar is that of a maker of manure; and it may have to be more highly organized than an earth-worm so as to perform its special duties in unpromising circumstances. The loose, recently-driven sand, from which all salinity can scarcely yet be leached, the dry, harsh needles, the enormous appetite of the insect — such are the materials and such the impulse with which Nature fulfils a magnificent purpose.

Swift declared that whoever makes two ears of corn, or two blades of grass, grow upon a spot of ground where only one grew before does essential service to his country. The sand-caterpillar and other living instruments of Nature that prepare hostile soil for the first single blade of grass, are they not entitled, also, to some sort of recognition?

To deal particularly with the spinner of sand, let it be said that the few caterpillars sent in spirits to a Museum did not reveal anything upon which to establish the identity of the perfect insect. It therefore became necessary to study the history of the insect throughout its transformations. First attempts to domesticate the caterpillars were successful beyond expectations. They were found to be tractable, or indifferent, under restraint, content and healthful under novel conditions, and submissive to frequent disturbances.

Disappointment having attended many attempts to discover the sand-spinner in the pupal state, it was necessary to confine the larvae and await developments. To this end a dozen were housed in a capacious tin half filled with damp sand, well supplied with casuarina needles strewn on the surface, and enclosed with wire gauze.

The period of the larval stage was not definitely ascertained; but it is safe to assume that it is limited to a month. In the course of a fortnight four had passed into pupae, having converted sections of their silk-lined shafts into cocoons. These were transferred to a glass jar containing damp sand, over the mouth of which linen was stretched and secured.

In its early stages the pupa fidgets on the slightest disturbance; but presently becomes insensible to the lightest touch. The chrysalis is three-eighths of an inch long and dark brown in colour.

On the fourteenth day the perfect insect emerged — a plump moth, silvery grey with pale brown smears, and apparently more comfortable in the dark than in daylight. With nothing to commend it in appearance, the moth is far less engaging than the active, eager, ever-hungry caterpillar; but it displays one quality that excites pity — almost furious resentment of the restraint upon its liberty. With one exception, the moths emerged from the cocoon during hours of darkness.

These specimens and observations were duly communicated to Dr. A. Jefferis Turner, of Brisbane, and from him came an assurance of new knowledge having been added to entomology.

Since it seemed possible to obtain more intimate knowledge of the life-story of the humble little stranger which conceals its doings in the sand, and under the veil of night, further efforts were made. Two full-grown caterpillars being confined in a glass jar half filled with sand and rationed with casuarina needles, both, as fortune would have it, afforded opportunities for the observation of their secretive ways. For two days each seemed to be content to lie passive, just covered with sand. Then both excavated shafts from the surface to the bottom of the jar, one following the inner surface, and thereby exposing the full depth of the shaft. In the making of the shaft the sand was displaced, not removed. the side being compacted until it was firm and smooth.

Food was drawn to the bottom in about half inch lengths. The insect emerged from the shaft, seized the end of a needle, backed to the trap-door mouth, descended tail first, bit off a convenient portion and drew it to the bottom; reascended, drew down a further length, retired with another convenient piece, and so on, to eat and repose.

Four days elapsed before the next process towards security and comfort was undertaken — the silken lining of the shaft, a slow work, apparently pursued with that economy of material in which Nature often rejoices. On the sand-face the shaft in section was delicately cased, but the glass side was not blurred with a single thread.

In his first letter on the subject, after receiving specimens of the moths, Dr. Jefferis Turner remarks that they represent a very interesting discovery. “Not only is this a new observation, but the moth is unknown to science, and its larval habits are most unexpected in the group to which it belongs.” He adds that it belongs to a very large and cosmopolitan family and to the sub-family of CRAMBIDAE, and that he thinks “it is one of the large genus CRAMBUS, though I will not commit myself to this absolutely until I have made more detailed examination. The species of CRAMBUS are mostly grass-feeders, and I believe none of them has habits anything like those you have discovered. Perhaps we may name the species CRAMBUS AMMONTHES— that is to say, ‘A Spinner of Sand.’”

Though the sand-spit is riddled with silk-lined shafts, each caterpillar lives a solitary, independent existence. The whole scheme may be said to represent an organized plan for the conversion of a waste material into a fertilizer, with but little loss, as it would seem, either in bulk or weight. So evident is its singleness of purpose that each humble insect might be deemed to be capable of realizing that its period of activity is far too brief for slackness — that waste of time and opportunities is not to be tolerated.

It is a beneficial work silently performed, and unostentatiously, too, save for the flickering here and there of the disappearing standards; performed, too, without fumbling or blundering by creatures that most of us regard as composed of little else than disagreeable “squash.”

Under natural conditions, a blank exists in the life-story of the insect. Though it is quite easy to obtain specimens of the larvae during a period of six months of the year, and to get them to pupate in confinement, so far not a single specimen of the pupae has been found in the sand or elsewhere. Larvae are to be found in all conditions of size and age, even to the state when they appear to be on the verge of transformation, the grey tint of the body changing to ivory yellow; but, though the pupae of other insects are frequently noticed, this stage is at present a problem except under artificial conditions.

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Last updated Wednesday, March 12, 2014 at 13:32