Years ago scientific visitors to a coral islet found almost innumerable sea birds and eggs. The multitude of birds and their prodigious fecundity inspired the thought that the “rookery” for the whole breadth of the Indian Ocean had been discovered. Investigations showed that the islet was also the abiding-place of a certain species of lizard which subsisted entirely on eggs. It was calculated that not one egg in several hundred was hatched out; yet in spite of such an extraordinary natural check the islet was enormously overpopulated. Thousands of birds every year laid eggs for the maintenance of fat and pompous reptiles, without reflecting that there were other and lizardless isles on which the vital function of incubation might be performed without loss. Years after other men of science sought the isle. Birds seemed to be as numerous as ever, but the lizards had disappeared. Had the birds been wise enough to perceive that the plague of lizards had been sent as reproof for overcrowding, or did the lizards become victims to physical deterioration incident upon gluttony and sloth?
“Into every instinctive act there is an intrusion of reasoned act.” No doubt; but in the case of the terns—sea-frequenting and sea-loving—which had not the wit to lay their eggs beyond the reach of spring tides, the reasoning is the merest intrusion. Yet an instance of what seems to be the reasoned act of a wasp may be cited. The insect had selected a dead log of soft wood as a site for its egg-shaft. It was at a spot to which the occupations of the season took me daily, so that the boring operations were watched from beginning to end. The work was done rapidly and neatly, and when all was ready for the deposit of the eggs the insect constructed from papier-mache-like material a disc-shaped lid exactly fitting the mouth of the excavation, to which it was attached on its upper edge by a hinge. Then round and about the disc similar stuff was plastered, so as to form an irregular splash, imitative of a bird's droppings to the-degree of perfect deception. In the centre was the lid with the hinge, and whensoever the insect visited its nursery the lid swung up, closing behind it. On departure it fell into position. Unless the insect by its presence betrayed its secret, the shrewdest observer at close quarters would have been misled.
There are reasons for the belief that green tree-ants understand and respect the laws of neutrality. There are several communities in the mango-trees, and since some of the trees overhang the fence, the top wire is used as a highway. When a gate is opened traffic is suspended. In a minute or two of a busy day there will be considerable gatherings on the latch-style, and if the intervening space is narrowed by the swing of the gate the impatient insects begin to make a living bridge across the perilous gap. At one particular gate, which is opened and shut many times a day, it has been noticed that the ants never seem to resent interruptions or to be vexed by them. If they happen to get on the hands or fingers, they submit to be restored to the gate; but go to the formicary on the mango-tree half a dozen yards away and offer a friendly finger, and you will find dozens of pugnacious individuals ready to defend their home. Do they recognise that they are but pilgrims of the fence, enjoying certain rights on sufferance, that it is a path of peace on which belligerents must not intrude, a neutral tract under the custody of the law of nations, which ants, as well as men, must respect? Whatsoever the reason, the deportment of the truculent ant on the highway is that of an upholder of peace at any price. It is to be doubted if the animal world holds more illustrious examples of heroism than a green tree-ants' nest. Two or three individuals may be despised as long as their assaults are confined to the less sensitive parts of the body; but let a huge colony up among the branches of an orange-tree be disturbed, and the first army corps instantly mobilised, and it will not be cowardly hastily to retreat. So eager for the fray are the warriors, so well organised, so completely devoted to the self-sacrificing duty of protecting the community, that two distinct methods of advance and attack are exercised forthwith in the midst of what appears to be calamitous confusion. Swarming on the extremity of the branches among which the formicary is constructed, the defenders, projecting their terminal segments as far into space as possible, eject formic acid in the direction of the enemy. Like shrapnel from machine guns, the liquid missile sweeps a considerable area. Against the sunlight it appears as a continuous spray, and should one infinitesimal drop descend into the eye the stoutest mortal will blink. Attacks are made singly and in detachments. Heroes actually hurl themselves from the branches, and, failing to reach the enemy, run along the ground and, scaling his legs, inflict punishment on the first convenient patch of unprotected skin. Detachments muster in blobs, fall in a mass to the ground, and charge. If one of these forlorn hopes happens to be successful, the observant man will retire with little of his dignity remaining.
It is interesting to note how readily birds acquire tastes for the sweet fruits which man cultivates. One of the honey-eaters, the diet of which ranges from nectar to the juice of one of the native cucumbers, as bitter as colocynth, has become an ardent advocate for the thorough ripening of bananas. While on the plant the fruit is not appreciated, but after the bunch has been hung for a week or so and the first fruits are changing colour the bird is enthusiastic. Formerly bunches were ripened in a thatched building for the the most part open, and the bird got the very best of the bunch. Now the process takes place where the bird has to venture through wire-netting. It has no fear, entering without ceremony, loudly complaining when inadvertently disturbed, and flying to other parts of the house to express remonstrance when the supply is exhausted.
Scarcity of surface-water sharpens the powers of observation of some birds and increases the trustfulness of certain species towards human beings in a region wherein they are held to have rights on equality with those of their superiors in the animal world. For years, during the few weeks which generally intervene between the disappearance of accustomed water reserves and the beginning of the wet season, with its super-abundance, the metallic starlings have been wont to obtain refreshment from a hollow far up a huge tea-tree, the supply in which seemed to be inexhaustible. The tyrant's plea, necessity, ordained the destruction of the never-failing tree, and now the starlings descend by the hundred into the deep and shady ravine whence water is pumped, and drink also from the cattle-trough and bathe therein with noise and excitement of happy children on the beach. It is quite within the mark to compute the starlings by the hundred. The trough is edged nearly all day long by thirsty or dirty birds, while scores sit round among the shrubs waiting turn and commenting on the frolics and splashings of others in excitable tones. When, perhaps, there are but a poor dozen or so round the trough, you may chance to see the birds in attitudes more varied than those of Pliny's doves, and catch the shadows of burnished necks darkening the water, as in that famous mosaic, and even the glistening reflection of the red, jewel-like eyes. Other birds, with far less assurance and shrill clamour than the lovely starlings, visit the trough regularly and by the score. Two species of honey-eaters are seldom unrepresented. The barred-shouldered dove, the spangled drongo, the noisy pitta, the red-crowned fruit pigeon, the pheasant-tailed pigeon, are less frequent visitors; and though the purple-breasted fruit pigeon—the most magnificent of all—talks to his mate in coarse gutturals from the trees above, he has not been seen actually drinking. So shy and furtive a bird would choose his time for refreshment when there is little likelihood of interruption. In the ravine there are often metallic starlings by the dozen, and little green pigeons—for those domiciled come and go at all hours of the day. Occasionally a sulphur-crested cockatoo comes sailing down to the diminishing pool through interwoven leafage noiselessly as a butterfly; but scrub fowls, scared by the apparition in white, scamper off with a clatter, scattering the dead leaves. In such narrow quarters, birds are under restraint, and show anxiety and apprehension. There is no sport or play. They drink quickly and with faculties strained, and flutter off excitedly on the least alarm. Well may they be suspicious, for is not the cool spot attractive to the sly enemy, the green snake, which conceals its presence by faithful resemblance to the creepers among which it glides? Here, too, come millions of industrious bees, and in the dusk the big pencil-tailed water-rat, which the masterful dog kills with as little ceremony as he does the bird-scaring snakes.
It was late for cockatoos to start on their daily flight to the mainland from the big tree close to the twin palms half-way up the hill, and as they flew hastily and in close company they scolded each other in unmannerly terms. The language must have been vexing, for as they sped along far above the passionless sea one jostled the other. It was just the sort of action to provoke hungry, peevish birds to vindictiveness. That which had been jostled turned on the offender with angry shrieking, and instantly a clamorous fight was in progress. Claws became interlocked, and they fell each with distended crest, like a gilt-edged cloudlet following the setting sun. Shadow and substance met with a splash. The sea momentarily swallowed the combatants. Then a yellow note of exclamation appeared, and with laboured flutterings, using his enemy as a base, one rose and struggled to the beach oaks. Frantic wing-beating showed that the other bird was in serious difficulties. It was a hundred yards out, but the enjoyment of a sunbath after a sea frolic enabled one to proceed to the rescue without preliminaries. Half drowned and completely cowed, the bird was now confronted by a more awful peril than that of the sea. A bedraggled crest indicated horror at the steady approach of the enemy man, whose presence stimulated the sodden bird to such extraordinary efforts that it succeeded in rising and in making slow, low flight to the beach.
At dawn a bat flew into a spider's web spun during the night, the extremities of the wings being so entangled that struggling was almost impossible. A big spider pounced on it. Not a minute elapsed from the entanglement until the bat was released, but the venom of the spider had done its work. There was not a sign of life. The spider is dark grey in colour, bloated of body, slothful, and of most retiring disposition. Huddled up into almost spherical form, it lurks in dark places, which it soon makes insanitary. In the open it crouches among dead leaves which have gathered in the fork of a tree, and will construct a web which spans the coconut avenue with its stays. From one aspect its rotund body invites a good-humoured smile, for the marking exactly simulates the features of a tabby cat, well fed, sleepy, and in placid mood. Venom of virulence to kill a bat almost instantly would be severe enough to a human being. This dirty, obese spider deserves little consideration at the hand of man.
A moonless, cloudless night. The little praam takes the ground in the bay a few yards from the beach, and in the midst of a constellation of “jelly-fishes” spherical in form and varying in size. The larger are so many pale blue orbs floating lazily in a luminous mist, the only visible manifestation of life being a delicate but rhythmical deepening of the central hue. The wash of my wading seems not to affect them. I become conscious of the sudden appearance and swift disappearance of lesser spheres of startling brilliance. They emerge from nothingness, pause for a moment, and shoot towards me with extraordinary impulse. Each is a mere globule, resplendently blue. The tint intensifies as with accelerated velocity the atom flies until of its own excessive energy it explodes with a shell-like flash, leaving a sinuous trail of golden light. To burst into sight, gather force, to flash and slowly vanish—such is the sum of life of a speck of sea-jelly. To be the centre towards which scores of the watery meteors gravitate, to witness their apparently spontaneous beginning, their swift, brief, but ineffectual career and lingering end, delights this night of darkness. How many of the race of man are there whose post-mortem glory outshines life tenfold?
Beneath a slab of dead coral on the reef there was revealed one of those primitive and curious marine animals which has no common name, but which science recognises as SYNAPTA BESELLI. It is a relation of the béche-de-mer, of snake-like form, with a group of gills differentiating the head. Playing about it were three or four little fish which immediately took advantage of the only remaining cover, the body of the Synapta, snoodling beside it so artfully that they were quite concealed. The protector did not appear to resent the close company of the fish, which remained perfectly motionless. In a few seconds the Synapta began to extrude its feathery gills, which had been partly retracted on disturbance. I counted the gills, and while my forefinger indicated the sixth, a little fish, not previously noticed, appeared at the focus and edged off to the margin of the pool, now and again making decided efforts to regain its sanctuary. It was about an inch long and a third deep, ruby red, with pink undersides and pink, transparent fins. Three narrow bands of silver edged with lavender extended across the shoulder. Life gave it jewel-like lustre. The companionship between the slow and feeble Synapta, one of the most primitive of sea things, and the brilliant, agile fish may be another instance of commensalism.
No one who parades a coral reef can fail to be impressed by the various means adopted by its weaker denizens to evade the consequences of conspicuousness. Among the vast multitude of creatures, mostly hostile to each other, few are more remarkable than the crabs, not only on account of form and habit, but for care of themselves during the periodic casting of their shells. They therefore represent an entertaining study and a never-ending source of pleasure to the observer, who, as he happens on some fantastic member of the family, wonders, remembering his Shakespeare, what impossible matter will Nature make easy next. Dreamy little ripples were laying on the strands sprays of seaweed, torn from the reef which was not quite out of the influence of the easterly swell. The conditions were ordinary, but one fragment made itself noticeable by slight, almost undiscernible, but still distinctive efforts to regain the water, whence it was separated by a few inches. Seaweed alone was visible as it rested on the palm of the hand. Presently it moved hesitatingly and with infinite slowness, and, being reversed, revealed itself as a “watery” crab under living disguise. The specimen was sent to the Australian Museum, Sydney, where it came under the hands of my friend Mr. Allan R. McCulloch, who devotes himself to the phenomena of the sea; and since his references to it are explicit and authoritative, they will be more acceptable than generalities from an uninformed pen: “The crab you sent is the second specimen known of ZEWA BANFIELDI, which I described from a dried specimen received from you some years ago. Not only the species, but the genus also, was unknown until you gave me the opportunity of describing this interesting beast. It is one of the spider crabs, or Oxyrhynchus, most of which have long horns projecting from the rostrum, and are more or less thickly covered with stiff curled setae, to which seaweeds, sponges, and other marine growths—selected according to the taste of the bearer—are attached. When these crabs shed their shells, which they must do periodically to allow of growth, they retire to a dark corner and draw themselves out of a slit between the back and the abdomen, legs and all, which must, I imagine, be a delicate and somewhat painful proceeding. After emerging, they are, of course, quite soft, and the setae on the carapace and legs are flexible. The crab then selects choice bits of weed from its old shell and fastens them to itself by the setae, which soon curl at the tips like the tendrils of a vine, and so hold them firmly. The weeds and sponges, requiring no roots, but merely a secure base, readily grow in their new position, and so cover their host with a sheltering disguise, enabling it to sally forth in quest of fresh loves and other adventures. I am sending the reprint with the original description and figure, also a sketch of the crab with its weedy garments. Much of the weed had become detached on its arrival here, which is, perhaps, fortunate, since the sketch would otherwise have shown merely a cluster of weeds.” It could be well wished that the specimen had retained the whole of its floral cloak, for then the sketch would have shown its deceptive qualities in perfection. Masquerading as a spray of seaweed, the crab eludes its enemies, the mask being of such high order that even man, with his perceptions, does not penetrate it unless he exercises his reasoning faculties. Because he knows that a spray of seaweed is not endowed with independent movement, when it does walk about he, at first, is as incredulous as was Macbeth when told of that “moving grove” of Birman.