IN TOUCH WITH NATURE

Otago Daily Times, Issue 20710, 7 May 1929, Page 2

IN TOUCH WITH NATURE

THE STONE-FLIES. By J. Drummond, F.L.S., F.Z.S. Near fresh water, notably running streams and the borders of lakes, there may be seen, even in this month and all through the winter, but much more abundantly in the early spring and in summer, hosts of insects, with subdued colour schemes, using their four wings to fly slowly. These are the stone-flies, whoso life histories in New Zealand at least have not been thoroughly worked out. One species, probably the most abundant in New Zealand, is grass-green in general colour. Its fore-wings are bright green and narrow, its hind-wings pale green and very broad, its legs green, but its abdomen is brown. In its early stages it is agnatic, very active in the water, difficult to capture, voracious, swift in pursuit of grubs, of the May-flies and of other insects, following them amongst stones in the bed of a stream and seizing them with its powerful jaws. In its turn, it is pursued by trout, providing them with an important food supply. Mr G. V. Hudson, Wellington, has given some attention to these stone-flies. He finds that the grubs grow slowly, more than a year may be spent in reaching maturity. In spite of their aquatic habits, they can travel fairly long distances on land, especially towards the end of their grub stage. At that stage, it is impossible to confine them in a shallow vessel, as, in order to get away, they immediately climb out of the water. In natural conditions, when the great change from grub to perfect insect is imminent, they leave the water and cling firmly to a stone, or to the stem of a plant, usually near the edge of the stream in which they spent their grubhood. The skin dries and then cracks along the back, and out comes the perfect insect, whose first action is to dry and expand its wings in anticipation of its new and_ highest faculty, flight. The empty skins of the grubs are often seen. The positions in which they are found sometimes show that the grubs travelled a long way from water before the perfect insects emerged. Mr Hudson has found the skins clinging to the stems of trees five feet above the ground and 15 yards from the bank of a stream. Another New Zealand stone-fly is black and shiny. As a grub, it is greenishbrown, spotted and striped with grey, its eyes are black and prominent, and with its long, powerful legs it crawls agilely in even the strongest currents. To change into a perfect insect, it leavesthe water and usually crawls on to an exposed stone. Those who wish to study these insects and to get a glimpse into their most fascinating lives, should follow the plan adopted by Mr Y. T. Chu, a member of the staff of St. John’s University Shanghai, who has reared Chinese stoneflies. When he took pieces of small stones quickly out of the water he found stone-fly grubs—he gives them the more elegant title of nymphs—on the underside. There they stayed motionless in order to escape notice, or they ran all over the surfaces of the stones and suddenly dropped off into the water. When collected in a small pan covered with, water the larger ones fiercely caught hold of the smaller .ones, or they climbed to the sides of the pan in efforts to escape. Kept longer in the pan, they stood up and moved their bodies up and down, in order to set the water in motion for better aeration. They , soon died if kept in too much water, but not if in shallow water in an open pan. The carnivorous grubs were equipped on their lower jaws with pointed curved teeth, fitted for grasping and biting. The vegetarians’ lower jaws were blunt, and were equipped with chewing apparatus. In grown-ups the mouth parts are weakly developed, Mr Chu has , reared stone-flies from the nymph stage to the grown-up stage. He has fed the carnivorous forms with the nymphs of May-flies and the grubs of midges, and the vegeteriana with decaying leaves. The cast skin of a nymph is a perfect specimen for a study of the insects’ outward anatomy. By rearing both nymphs and perfect stoneflies, Mr Chu has studied species all along life’s track, and has discovered characters that define different species. The oggs, small, seed-like, and very numerous, usually washed off in masses into running water by the females, took almost a month to hatch. Each infant stone-fly crawled from its eggshell through a lid at one end, and immediately began to fend for itself. After spending more than a month watching H ie >J e Y e Jopnient 0 pnient of Chinese stone-flies, Mr Chu, who is a specialist in the classification of these insects, and is fascinated by their physiology and their domestic affairs, describes his experience as one of the most interesting pieces of w °rk I have ever done.” His work shows that although it may he difficult to rear stone-flies, patience and a little knowledge bring success.

Only seven species of stone-flies have been described and classified in New Zeaby entomoiogists, but in one season T. r R - J-Tilly,ard and Mr W. G. Homes discovered four times as many species. The order of the atone-flies, the Plecoptera, folded uings, is > particularly well represented in the colder parts of the Dominion. A large proportion of the fresh species come from Otago and Southland. New Zealand and Australia are rfich an species, and the stone-fly faunas in the Commonwealth and in the Dominion resemble each other, also the stone-fly founa of Southern Chili and Patagonia. Their fossils have not been found in New Zealand or in Australia, but impressions made on the rocks by a few small wings and grubs are evidence that 'stone-flies lived in Europe in the Jurassic Period, fairly early in the world’s geological history.

The internal anatomy of a stone-fly has interesting features. Its oesophagus is enormous, but its true stomach is small, and the brain is tiny. The grub breathes by gills, and probably likes water that is strongly aerated. They seem to favour mountain streams, torrents, and waterfalls. They do not like water that descends from glaciers, although they are remarkable for their capacity to endure cold. It is thought that they may need warmth at some stage of their development, and that glacier streams cannot give it to them. In Canada a stone-fly nymph often comes up in cracks of ice, and here casts its skin. In some species the eggs, after they arc laid, arc carried about by the female, for reasons unknown. The ample wings are .not strong, and in several species the mule’s wings are much reduced in size, contrary to the rule amongst insects that, when there is a difference in powers of flight, or even in the size of the wings, the male is superior to the female. The wings of a male of a species found at Loch Tnnna, in Arran, Scotland, are merely useless rudiments.. Stone-flies' unattractive outward appearance protect them from collectors to some extent. They arc so fragile that unless good care is taken of them they soon go to destruction. Like may-flies , alder-flics, dragon-flies, lacewinged flies, saw-flies, caddis flies, and scorpion-flies, they are not true flies. They belong to the Neuroptera, (he Nerve-wings, their \ ings being reticulated with veins or nervures. They have a slight metamorphosis, and in (he life history of each individual there - are two abrupt chapters, one dealing with life in the water and the other with life in the air.