VIGNETTES FROM NATURE.

Otago Witness, Issue 3337, 27 February 1918, Page 55

VIGNETTES FROM NATURE.

XXIII.—A WAYSIDE POOL IN TARANAKl—(Continued.) t By G. M. Thomson, F.L.S. I do not know how many kinds of water-beetles this little pornl contains — certainly more than one species is present. Water-beetles belong to several (three at least) families of Coieoptera, but the name is chiefly applied to those which belong to the Dytiscxhe. These animals are very manifestly adapted for an aquatic life. The body tapers at both anterior and posterior ends, and so offers little resistance as it moves through the water. The same purpose is also served by the smooth and polished surface of the elytra, and, in fact, of all parts of the hard external covering of the body. The forelegs are clawed, and are used almost entirely as organs of prehension, either for seizing the prey or to anchor the body to pond-weeds or other submerged objects. The other legs, and especially the third pair, which constitute the principal means of locomotion, are long and powerful, and the claws are in a more or less rudimentary condition. These limbs are flattened and oar-like, and furnished with a row of stiff bristles, which can be made to stand out in the form of a fringe or to fall against the surface of the limb in such a manner as to be hardly discernible. Thus the beetle, when swimming, can widen the blade of its oar when propelling its body through the water, and reduce the resistance offered to a minimum during the backward stroke, just as an oarsman does when he is " feathering." Water-beetles are giited with considerable powers of flight, though most of. them are unable to start on the wing unless they first obtain a foothold on the bank, on a floating object, or on the exposed portion of an aquatic plant. They usually fly at dusk or during the dark hours of the night, and migrate over considerable distances in search of suitable ponds in which to obtain their food or to deposit their eggs. Furneaux, describing the habits of British water-beetles—-and in these respects the animals resemble one another wherever they are found, — says: "In many cases these insects terminate their flight in a very peculiar and abrupt manner. Finding themselves over the surface of a piece of water, they suddently close their wings and simply allow themselves to fall into it. It is probable that in this matter they are, enabled to judge of their position with regard to the water by the sense of sight only; hence it is easy to understand that they may often be deceived by reflections from bright surfaces other than those of ponds and streams. It has often been observed that water-beetles, thus deluded, have allowed themselves to fall on the grass roof of a, greenhouse. On one occasion, too, I myself observed a large one drop directly on a garden path over which a pail of water had just been thrown." I do not know the species of waterbeetle which are to be found in this pond, but two species were met with, one of which was especially common, and which between its excursions to the surface to renew its air-supply regularly- dived into the layer of very soft mud at the bottom of the water. Besides these and the dragon-flies, there are very many other insects belonging to different orders and families, especially of flies, many species of which breed in the mud at the edge of the water. Many of them also—and these are mostly very small forms—have the power of running about on the surface, and any one who desires to learn the effects" of surface-tension of liquids as exhibited by animal life cannot do better than study the behaviour of water-gnats, pond-skaters, and other insects which run and slide about on the surface of freshwater pools. Pond-snails are very abundant, feeding on the. weed which fills so much of the water• • but I do not know the mollusca well enough to identify the species. Crustacea are represented only by some minute forms belonging to- the Ostraeoda and Copepoda, and to the division Branckiopoda or gill-footed Crustacea, so called because the breathing organs are attached to the limbs. All these small forms belong to the group formerly and more familiarly known under the common name of Entomostraca. I don't apologise for these " lang-nebbit " names; there are no popular names for the creatures referred to which are not misleading. It is somewhat remarkable at first sight that this pond does not contain any of the fresh-water crayfish (Paranephrops), which are so abundant, as a rule, in streams throughout New Zealand. The reason, no doubt, is that the pond is of very recent formation, and no crayfish have found ijheir way into it; and this suggests certain ideas as to the facilities for distribution which some animals possess as compared with others. Crayfish cannot live long out of water• they cannot, therefore, cross damp meadows from pool to pool, as, for instance, eels regularly do at night. Thev are too large to be carried accidentally by birds. The females carry the eggs for months attached to the swimmerets on the underside of the abdomen, and the young, when batched out, at once take refuge in the bed of the stream into which they are born under stones and other places of concealment. Besides, thev are even less able to be long out of the water than the This is almost certainly the explanation of their absence. Had the head of this valley contained a permanent streamlet, however small, it would probablv have been naturally stocked with crayfish from the larger stream into which it flowed, whereas a mere damp swamp with no permanent stream would not likely entice them. At any rate they have not got up to the head of this little valley. The most abundant Branchiopod crustaceans are the pretty and curious little

Daphnias, popularly known as {' waterfleas," from their jumping method of progression. In the little animals the body is enclosed in a bivalve shell, which is so transparent that most of the internal organs can be seen more or Jess clearly through it. The shape of the shell is somewhat oval, ending . below in a long, sharp beak or spine. The anterior end is rounded and produced forwards and downwards into a little sharp beak, near which the minute antermules are seen. Behind the beak lie the prominent compound eyes, each formed of many facets or lenses. The most remarkable development is that of the second antennae, which project upwards like a pair of large arms carying numerous plumose branches. These are, the principal organs of locomotion. When swimming the animal waves them with a strong downward stroke, all the branches and plumes being spread out like rigid fan. On the upstroke these are all relaxed and become limp, so that the whole fan slips back easily to the vertical position ready for the down-stroke. This movement causes the animals to progress through the water by a series of jerks or jumps, mostly upwards, the body sinking down through the water when the limbs are at rest. At the back of the carapall, apparently between the body and the valves of the shell, but. in reality, of course, on the dorsal side of the animal, the little heart can be easily seen, and its beats counted. At certain seasons of the year the females can be seen carrying their eggs stored in the same region, between the lower part of the body and the valves of the shell. The abdomen, with its attached branchial feet, is moved fairly regularly between the valves of* the carapace in front, so as to keep the plumose gills waving in the water, which supplies them with dissolved oxygen. These little Daphnias are very espec.ally in the morning and evening. The Ostracodes are also enclosed , in bivalve shells, but' none of the appendages are external, and the shell can be shut tight like that of a mussel. When it opens the limbs are projected at one side, so that the little animal can swim about with a paddling movement like a dog, or creep about freely on the bottom. The most conspicuous one here is a small round dark-green species, originally described by me as Cypris viridis, about as large as a turnip-seed. It occurs frequentlv in great numbers. Many of the' elongated forms seldom swim far from the bottom, and a number of species were first described by Professor G. O. Sars, of Christiania, who hatched them out from parcels of dried mud which I sent him. These portions of mud were gathered from dried-up pools in the Auckland and Canterbury districts and in the Taieri Plain, and from these he hatched out over a dozen species of ostraeods. Another common group of crustaceans — the Copepoda, or oar footed Ehrimps—are represented by the little Cyclops, which are like miniature long-tailed lobsters. Their scientific name is derived from the large globular eye formed of two compound eyes which is placed in the front of the head, like that of the one-eyed giants of Greek mythology. Great numbers Of these animals, belonging -to two or three species, fire very common in the pools of this district. This autumn afternoon I paid a farewell visit to the little pond, and, seated on a grass bank at. the side of it, looked down the little swampy valley beyond the cross-road. The bottom was full of waving beds of bulrushes, fringed here and there with clumps of willow, while the sides were heavily grassed, and carried occasional patches of gorse. Where the stream valley bent away to the right, the high ground was planted with pines and cypresses, and the scene might have been anywhere in England rather than in New Zealand, were it not for the inevitable box-thorn hedges limiting the fields. But behind all and closing the vista rose the beautiful cone of Mount Egmont, right north of me, and showing a perfect outline from this point of view, with only a few streaks and patches of snow showing near the top, and with great banks of cloud rolling and drifting off to the left of the peak. My seat would have been made unbearable by the mosquitoes, ' whose larvte swarmed in the pool, but for a cool southerly breeze,' which drove them to seek cover. The water at my feet was puddled by the feet of cattle, and the herbage—even the very mshes—were cropped close by them. This rich land carries a very heavy stock, and the paddock behind me was full of young and very curious steers. The water at first seemed still enough and empty, but a few minutes' close observation revealed not only all the creatures I have been writing 'about, but a vast number more—far too many, indeed, to note without careful collecting. An occasional tadpole wriggled in a puddle near inshore ; while a few yards out, among the large oval floating leaves of the Ottelia, a perch flapped about near the surface, as if in pursuit of a. small frog or tadpole of a more adventurous type than its fellows. A large dragon-fly swept past me, and made a dash at a moth, but just missed it The- moth, however, in its downward swoop, struck the water, and while struggling to recover itself was attacked by another and smaller species of insect—a predaceous fly. It escaped its second assailant, but was unable to get away from the water, having probably wet its wings, and in the course of time it would probably find its way into the maw of a hungry frog or perch. Then just as I was writing these notes the shrill cry of a weka sounded out of the bulrushes, answered immediatelv by another further down the valley ; while a" large hawk overhead hovered at no great distance. In Otao-o we protect hawks because they attack rabbits; in Taranaki (where there are no rabbits) the farmers destroy them, as thev are too fond of pilfering chickens, and the gunmen (I don't call them sports) shoot them because they eat young quail and pheasants. One interesting fact was noted. The

bottom of many of the shallow puddles, when looked at closely, was seen to be alive with very slender red worms, the bodies of which, seemed to bo buried in the mud, while tha free end 3 waved about in the water, keeping up a curious vibratory movement. They must have been attached at a considerable depth, for they withdrew into the mud on the slightest disturbance, and could not be dislodged from the bottom by a stout walking stick. As I returned from my afternoon strol} I pondered over the extraordinary amount and variety of the which occurred in this little pond. This is all' the more remarkable in that it is an artificial sheet of water of quite recent formation. The country is geologically recent, and the nearer one gets to Mount Egmont the more one- notices the absence of certain forms familiar in other regions of New Zealand. Yet here in this small area one would find matter for a lifetime study. I have referred only to a few of tne denizens of the pond. But there is material here which would keep the biological laboratory of a university stocked with matter for study indefinitely. The microscopical life is just as abundant and varied as lhat which the unaided eye can see, I am certain that if all our young people in our schools had the opportunity of making first-hand acquaintance with the plants ana animals of the district in which they live, the sum of human happiness would be greatly increased in the near future. The material is everywhere, the Interest is universal and easily intensified; but even to the majority of teachers Nature is a sealed book, and few there be who seek to open its pages.