King Solomon's Ring Read online

  So you skim with your net through the water plants in the pond, generally filling your shoes with water and mud in the process. If you have chosen the right pond and found a place where “something is up”, the bottom of the net will soon be swarming with glassily transparent, wriggling creatures. Tip up the base of the net and wash it out in the jam jar which you have already filled with water. Arrived home, you empty your catch carefully in the aquarium and contemplate the tiny world now unfolding its secrets before your eyes and magnifying glass.

  The aquarium is a world; for, as in a natural pond or lake, indeed as all over our whole planet, animal and vegetable beings live together in biological equilibrium. The carbon dioxide which the animals breathe out is assimilated by the plants which, in their turn exhale oxygen. Nevertheless it is false to say that plants do not breathe like animals but “the other way round”. They breathe in oxygen and breathe out carbon dioxide, just as animals do, but, apart from this, the growing green plant assimilates carbon dioxide, that is, it uses the carbon for the building up of its body substance: indeed, one might say that, independently of its breathing, the plant eats carbon dioxide. During this process it excretes oxygen in excess of its own breathing and, from this surplus, man and animals breathe. Finally, plants are able to assimilate the products of dead bodies decomposed by bacteria and to make them again available to the great cycle of life, which thus consists of three interlocking links: the constructors—the green plants, the consumers—the animals, and the decomposers—the bacteria.

  In the restricted space of the aquarium, this natural cycle of metabolism is easily disturbed and such a disturbance has catastrophic results for our little world. Many aquarium keepers, children and adults alike, are unable to resist the temptation of slipping just one more fish into the container, the capacity of whose green plants is already overburdened with animals. And just this one more fish may be the final straw that breaks the camel’s back. With too many animals in the aquarium, a lack of oxygen ensues. Sooner or later some organism will succumb to this and its death may easily pass unnoticed. The decomposing corpse causes an enormous multiplication of bacteria in the aquarium, the water becomes turbid, the oxygen content decreases rapidly, then further animals die and, through this vicious circle, the whole of our carefully tended little world is doomed. Soon even the vegetation begins to decompose—and what some days ago was a beautiful, clear pool with healthy growing plants and lively animals becomes a horrid, stinking brew.

  The advanced aquarium keeper counteracts such dangers by aerating the water artificially. Such technical aids, however, detract from the intrinsic value of the aquarium, whose deeper meaning lies in the fact that this little water-world is selfsupporting and, apart from the feeding of the animals and the cleaning of the front pane of the container (the algae on all other panes are carefully left alone as valuable suppliers of oxygen!), needs no biological care. As long as the right equilibrium is maintained, the aquarium itself needs no cleaning. If one denies oneself the larger fishes, particularly those that stir up the bottom, it does not matter if a layer of mud is gradually formed from the excreta of animals and from dying plant tissues. This is even to be desired, since it suffuses and fertilizes the sandy bottom which was originally sterile. In spite of the mud, the water itself remains as crystal clear and odourless as any of our alpine lakes.

  From a biological, as also from a decorative point of view, it is best to arrange the aquarium in spring time and to set it only with a few sprouting plants. Only plants that have grown in the aquarium itself are able to adapt themselves to the special conditions of the particular container and thrive, while all plants which one puts full-grown into an aquarium lose much of their original beauty.

  Two aquaria, separated from each other by only a few inches, have individual characters just as sharply defined as two lakes many miles apart. That is the attractive part about a new aquarium. When one is setting it up, one never knows how it will develop and what it will look like by the time it has reached its own particular stage of equilibrium. Suppose that one establishes, at the same time, and with the same inorganic material, three containers which one places close together on the same stand and plants all three with water thyme (Elodea canadensis) and water milfoil (Myriophyllum verticillatum): in the first, a dense jungle of Elodea may soon be flourishing which more or less eliminates the Myriophyllum, in the second the opposite may take place and, in the third, the plants may harmonize, and apparently from nothing there may spring a delightful vegetation of Nitella flexilis, a decorative green alga, branched like a chandelier. Thus the three containers can each produce an entirely different landscape. They would also have completely different biological properties, and be propitious for different types of animals. In short, although prepared under the same conditions, each aquarium develops its own little individual world. A certain amount of restraint and self-control is necessary to prevent oneself from interfering with the natural development of an aquarium. Even well-meant adjustments on the part of the owner may cause much damage. It is, of course, possible to set up a “pretty” aquarium with artificial foundations and carefully distributed plants; a filter would prevent any mud formation and artificial aeration permit the keeping of many more fish than would otherwise be possible. In this case the plants are merely ornamental, the animals do not require them since they derive from the artificial aeration enough oxygen for their maintenance. It is purely a matter of taste, but I personally think of an aquarium as of a living community that regulates its own equilibrium. The other kind is a “cage”, an artificially cleaned container which is not an end in itself, but purely a means of keeping certain animals.

  It is a real art to determine in advance the type of animal and plant community which one wants to develop in an aquarium, and to do this requires much experience and biological tact in choosing the right materials for the bottom, the situation of the tank, the heat and light conditions, and finally the plant and animal inmates themselves. A past master of this art was my tragically deceased friend Bernhard Hellman who was able to copy, at will, any given type of pond or lake, brook or river. One of his masterpieces was a large aquarium which was a perfect model of an Alpine lake. The tank was very deep and cool, and was placed not too near the light, the vegetation in the crystal-clear water consisted of glassily transparent, pale green pond weed (Potamogeton), the stony bottom was covered with dark green Fontinalis and decorative stonewort (Chara). Of the non-microscopic animals the only representatives were some minute trout and minnows, a few freshwater shrimps and a little crayfish. Thus, the animal inhabitants were so few that they hardly required feeding, since they were able to subsist on the natural microfauna of the aquarium.

  If one wishes to breed some of the more delicate water animals, it is essential, in the construction of an aquarium, to reproduce the whole of the natural habitat with its entire community of living macro-and micro-organisms. Even the commonest of tropical aquarium fishes are dependent on this condition, but their natural habitat is that of a small and not too clean pond which harbours exactly the sort of life community which automatically develops in the average aquarium. The conditions of our European waters, exposed to the variations of our climate, are much more difficult to reproduce indoors, and that is the reason why the majority of our native fishes are harder to keep and to breed than tropical species. You will now understand why I advised you to fetch your first water organisms out of the nearest pond with the traditional homemade fishing net. I have kept hundreds of aquaria of the most varied types, but the cheapest and most ordinary pond aquarium has always appealed to me particularly since its walls enclose the most natural and perfect life community that can be attained under artificial conditions.

  A man can sit for hours before an aquarium and stare into it as into the flames of an open fire or the rushing waters of a torrent. All conscious thought is happily lost in this state of apparent vacancy, and yet, in these hours of idleness, one learns essential truths about the
macrocosm and the microcosm. If I cast into one side of the balance all that I have learned from the books of the library and into the other everything that I have gleaned from the “books in the running brooks”, how surely would the latter turn the scales.

  3

  ROBBERY IN THE AQUARIUM

  How cheerfully he seems to grin,

  How neatly spreads his claws,

  And welcomes little fishes in

  With gently smiling jaws!

  Lewis Carroll, Alice in Wonderland

  There are some terrible robbers in the pond world, and, in our aquarium, we may witness all the cruelties of an embittered struggle for existence enacted before our very eyes. If you have introduced to your aquarium a mixed catch, you will soon be able to see an example of these conflicts, for, amongst the new arrivals, there will probably be a larva of the water-beetle Dytiscus. Considering their relative size, the voracity and cunning with which these animals destroy their prey eclipse the methods of even such notorious robbers as tigers, lions, wolves, or killer whales. These are all as lambs compared with the Dytiscus larva.

  It is a slim, streamlined insect, rather more than two inches long. Its six legs are equipped with stout fringes of bristles which form broad oar-like blades that propel the animal with quick and sure movements through the water. The wide, flat head bears an enormous, pincer-shaped pair of jaws which are hollow and serve not only as syringes for injecting poison, but also as orifices of ingestion. The animal lies in ambush on some waterplant; suddenly it shoots at lightning speed towards its prey, darts underneath it, then quickly jerks up its head and grabs the victim in its jaws. “Prey”, for these creatures, is all that moves or that smells of “animal” in any way. It has often happened to me that, while standing quietly in the water of a pond, I have been “eaten” by a Dytiscus larva. Even for man, an injection of the poisonous digestive juice of this insect is extremely painful.

  These beetle larvae are among the few animals which digest “out of doors”. The glandular secretion that they inject, through their hollow forceps, into their prey, dissolves the entire inside of the latter into a liquid soup which is then sucked in through the same channel by the attacker. Even large victims, such as fat tadpoles or dragon-fly larvae, which have been bitten by a Dytiscus larva, stiffen after a few defensive movements, and their inside, which, as in most water animals, is more or less transparent, becomes opaque as though fixed by formalin. The animal swells up first, then gradually shrinks to a limp bundle of skin which hangs from the deadly jaws, and is finally allowed to drop. In the confined spaces of an aquarium, a few large Dytiscus larvae will, within a few days, eat all living things over about a quarter of an inch long. What happens then? They will eat each other, if they have not already done so; this depends less on who is bigger and stronger than upon who succeeds in seizing the other first. I have often seen two nearly equal-sized Dytiscus larvae each seize the other simultaneously and both die a quick death by inner dissolution. There are very few animals which, even when threatened with starvation, will attack an equal sized animal of their own species with the intention of devouring it. I only know this to be definitely true of rats and a few related rodents; that wolves do the same thing, I am much inclined to doubt, on the strength of some observations of which I shall speak later. But Dytiscus larvae devour animals of their own breed and size, even when other nourishment is at hand, and that is done, as far as I know, by no other animal.

  A somewhat less brutal but more elegant beast of prey is the larva of the great dragon fly Aeschna. The mature insect is a true king of the air, a veritable falcon among insects, for it catches its prey when on the wing. If you shake your pond catch into a wash basin, in order to remove the worst miscreants, you will possibly find, besides Dytiscus larvae, some other streamlined insects whose remarkable method of locomotion at once attracts the attention. These slender torpedoes which are usually marked with a decorative pattern of yellow and green, shoot forward in rapid jerks, their legs pressed close to their sides. It is at first something of an enigma how they move at all. But if you observe them separately, in a shallow dish, you will see that these larvae are jet propelled. From the tip of their abdomen there squirts forth a powerful little column of water which drives the animal speedily forward. The end portion of their intestine forms a hollow bladder which is richly lined with tracheal gills and serves at the same time the purposes of respiration and of locomotion.

  Aeschna larvae do not hunt swimming but lie in ambush: when an object of prey comes within eye range they fix it with their gaze, turn their head and body very slowly in its direction and follow all its movements attentively. This marking down of the prey can only be observed in a very few other non-vertebrate animals. In contrast to the larvae of Dytiscus, those of Aeschna can see even very slow movements, such as the crawling of snails which therefore very often fall a prey to them. Slowly, very slowly, step by step, the Aeschna larva stalks its prey: it is still an inch or two away when suddenly—what was that?—the victim is struggling between the cruel jaws. Without taking a slow- motion picture of this procedure, one could only see that something tongue-like flew out from the head of the larva to its prey and drew the latter instantly within reach of the attacker’s jaws. Anyone who had ever seen a chameleon eating would at once be reminded of the flicking back and forth of its sticky tongue. The “boomerang” of the Aeschna is, however, no tongue but the metamorphosed “underlip” which consists of two movable joints with a pincer at their end.

  The optical fixation of its prey alone makes the dragon-fly larva appear strangely “intelligent” and this impression will be strengthened should some other peculiarities of its behaviour be observed. In contrast to the Dytiscus larva which will snap blindly at anything, the dragon-fly larva leaves animals above a certain size severely alone, even if it has been starving for weeks. I have kept Aeschna larvae for months in a basin with fish, and have never seen them attack or damage one larger than themselves. It is a remarkable fact that the larvae will never grab at a prey which has been caught by a member of their own species and which is now moving slowly backwards and forwards between the masticating jaws; on the other hand they will at once take a piece of fresh meat moved in a like manner on the end of a glass feeding rod in front of their eyes. In my large American sun-porch aquarium I always had a few Aeschna larvae growing up: their development takes long, more than a year. Then, on a beautiful summer’s day, comes the great moment; the larva climbs slowly up the stem of a plant and out of the water. There it sits for a long time and then, as in every moulting process, the outer skin on the back part of the thoracic segments bursts open and the beautiful, perfect insect unwinds itself slowly from the larval skin. After this, several hours expire before the wings have reached their full size and consistency, and this is attained by a wonderful process whereby a rapidly solidifying liquid is pumped, under high pressure, into the fine branches of the wing veins. Then you open the window wide and wish your aquarium guest good luck and bon voyage in its insect life.

  4

  POOR FISH

  Weed in the wave, gleam in the mud—

  The dark fire leaps along his blood;

  Dateless and deathless, blind and still,

  The intricate impulse works its will.

  Rupert Brooke, The Fish

  Strange what blind faith is placed in proverbs, even when what they say is false or misleading. The fox is not more cunning than other beasts of prey and is much more stupid than wolf or dog, the dove is certainly not peaceful, and of the fish, rumour spreads only untruth: it is neither so cold-blooded as one says of dull people, nor is the “fish in water” nearly so happily situated as the converse saying would imply. In reality there is no other group of animals that, even in nature, is so plagued with infectious diseases as the fish. I have never yet known a newly caught bird, reptile or mammal bring an infectious disease into my animal population; but every newly acquired fish must, as a routine measure, go into the quarantine aquar
ium, otherwise you may bet a hundred to one that within a very short time the dreaded minute white spots, the sign of infection with the parasite Ichthyophtirius multiliis, will appear on the fins of the previously installed aquarium dwellers.

  And regarding the alleged cold-bloodedness of fishes; I am familiar with many animals and with their behaviour in the most intimate situations of their life, in the wild ecstasies of the fight and of love, but, with the exception of the wild canary, I know of no animal that can excel in hot-bloodedness a male stickleback, a Siamese fighting-fish or a cichlid. No animal becomes so completely transformed by love, none glows, in such a literal sense, with passion as a stickleback or fighting-fish. Who could reproduce in words, what artist in colour, that glowing red that makes the sides of the male stickleback glassy and transparent, the iridescent blue-green of its back whose colour and brilliance can only be compared with the illuminating power of neon lighting, or finally, the brilliant emerald green of its eyes? According to the rules of artistic taste, these colours should clash horribly, and yet what a symphony they produce, composed by the hand of nature.

  In the fighting-fish, this marvel of colour is not continually present. For the little brown-grey fish that lies with folded fins in one corner of the aquarium reveals nothing of it for the moment. It is only when another fish, equally inconspicuous at first, approaches him and each sights the other, that they begin gradually to light up in all their incandescent glory. The glow pervades their bodies almost as quickly as the wire of an electric heater grows red. The fins unfold themselves like ornamental fans, so suddenly that one almost expects to hear the sound of an umbrella being opened quickly. And now follows a dance of burning passion, a dance which is not play but real earnest, a dance of life or death, of be-all or end-all. To begin with, strangely enough, it is uncertain whether it will lead to love overtures and mating, or whether it will develop, by an equally flowing transition, into a bloody battle. Fighting-fish recognize the sex of a member of their own species not simply by seeing it but by watching the way in which it responds to the severely ritualized, inherited, instinctive movements of the dancer.