IN TOUCH WITH NATURE.

Otago Witness, Issue 3888, 18 September 1928, Page 7

IN TOUCH WITH NATURE.

By

THE BOATMEN.

J. Drummond,

F.L.S., F.Z.S.

In ponds and stagnant water in New Zealand there are little insects embellished by shining yellowish-white marks, with four joints on their feelers, and with bodies convex above and flat below. They may be seen lying on the surface of the water backs downwards, and heads slightly under the surface. They are members of the family Notonectidce. This means back-swimmers. Popularly,' they are water-boatmen, an unnecessarily long name, which may be reduced to boatmen. By adapting themselves to their mode of life, they, ages ago, anticipated man in devices to get along in the water. Their long hind legs are furnished at the ends with hairy fringes. These are shaped like blades of oars, and are used as oars. By rowing or paddling, the boatmen send themselves through the water at an astonishing speed. The process is not the result simply of force from the use of muscles. They actually “ feather ” their oars in the same way as a skilled oarsman does, in order to avoid “ catching a crab,” and experience that befalls most people when they first learn to handle oars in a boat. As a boatman forces his legs against the water to make a stroke, the bristles on the blade stick out and give leverage. The stroke finished, the bristles collapse, and the leg is drawn forward, until the bristles stand out again in readiness for the next stroke. , The difference between the boatmen’s natural oars and the artificial oars used by human beings is that the boatmen do not raise their oars out of the water at the end of each stroke. If they were not furnished with the collapsible bristles, their rowing would be inefficient. They would merely go a short distance forward and a short distance backward, and there would be no progress. Their method of rowing has been compared to the North American Indian’s method of paddling. He does not take his paddle out of the water. Having made a stroke with the flat of the blade, he swists his paddle until its edge is presented to the water, while it is brought forward for the next stroke. This is a surprising adaptation, but it is less interesting, perhaps, than the boatmen’s method of breathing air. Some insects that live in ponds have an airtube at the end of the body As they keep the tip out of water, the air is received into the tube, and is passed through the body. Other pond dwellers have an air reservoir under their wings. They must come to the surface fairly often to fill it. Boatmen lie near the surface, with their legs spread like an oarsman resting, and with their heads below the surface and their tails above it. Air enters by air holes a space on the side between the wing cases and the body. It is passed through the respiratory system, is squeezed out at the junction of the wing case and the thorax, and ascends to the surface in bubbles. Boatmen have powerful beaks and efficient mouths. With these they suck the juices of other aquatic insects, but their mouths take no part in respiration. They connect with only the digestive system. A boatman’s mouth may be closed without any effect on the boatman’s breathing. If the airholes on its sides are clogged it will die of suffocation, although its mouth is open all the time. The airholes open into elastic tubes, which ramify through the body, and which may be bent and curved with the movements of the body, but are protected and strengthened by spiral wires of a white, horny substance. Each airhole has a fringe of hairs, which filter the air before it enters the tubes. There is no part that the tubes do not reach. They run through the wings, the legs, the muscles, and to every organ. Large and powerful wings are possessed by boatmen. They can fly directly from the water. When they wish to By, they dive a short way below the surface, assuming a perpendicular position, head upwards. Giving a smart stroke with the swimming legs, they dart to the surface. The stroke sends them a few inches out of the water. They spread their wings suddenly, and fly off, with a loud, dull, humming sound. In the water they seize other insects, clasp them tightly, drive their beaks into them, and suck their juices. A boatman hardly can be

induced to release its deadly clasp on a victim until the meal is finished. It swims about, holding the victim firmly pressed against its body, until the last drop of ju.ce has been taken.

Another inhabitant of stagnant water plentiful from Auckland to Otago, characterised by black and yellow lines, is a connection of the boatmen, and sometimes shares their popular name. Unlike the true boatmen, they swim with their backs upwards. They spend the winter in mud at the bottom of ponds. They have powerful wings, and when their ponds are dry they take to the air in search of fresh quarters. Attracted by light, they cluster in large numbers around lights on warm, damp nights. The males produce a chirping noise by rapidly rubbing their front legs across the front of their faces, and by moving the edge of the fore-wing over an organ like a rasp, on the back, in entomological literature they are the corixidae.

The latest observations of the musical efforts of grasshoppers, which a Wairoa lady inquired about a few weeks ago, show that in some species, the art has been well developed. Simple file-veins and scrapers are used, and lisps and rasps are produced. Some grasshoppers merelyset their wings humming in a continuous buzz of monotonous sound. This, perhaps, is the simplest musical expression, as it does not even include rhythm. But this simple monotone has been broken up by some grasshoppers into rhythmic intervals, with a surprising uniformity amongst members of the species. It is slower with cool temperatures, faster with high temperatures.

These rhythmic rasps or beats are regarded as the beginning of definite musical expression. Other grasshoppers have varied their notes and phrases, making new time-relations and sequences of sound. A little American grasshopper begins its song with a prolonged soft, lisping sound, made by rapidly shuffling its wings. This soon runs into a succession of short staccato lisps and ends with a rapid shuffling sound. In some cases the songs show that the instrumentalists have a remarkable manipulation of their scrapers over the veins upon which they play. One of these insects separates the upper edges of its wing-covers as far as possible, perhaps three-sixteenths of an inch, then allows them to close with such nicety of judgment that the scraper, striking only one or more teeth of the filevein at a time, produces a series of from 20 to 30 loud leisurely clicks.

A member of the burrowing group of spiders has attracted the attention of Mr D S. Armstrong, Bideford, Masterton. He describes it as the largest species of spider he has seen, some individuals reaching a length of one inch. It is power fully built. Its cephalo-thorax is flattened and dented and is like burnished sepia. Its abdomen is rotund, and is a faded slaty-brown. Its wicked-looking eyes glisten like tiny metallic spheres Its appearance is not reassuring, and when aroused it is aggressive.

“These spiders are very plentiful in the paddock where I am working,” Mr Armstrong writes. “ The country is hilly, poor in Nature, and is a habitat of the manuka. The soil is a shallow layer of black humus, descending abruptly to friable clay. In the surface layer these spiders thrive, if size and numbers are indications. At this time of the year August, and. I suppose, in the preceding winter months, they confine themselves underground in a torpid state. They may be found head downwards, snuggled securely at the bottom of an underground retreat which slants very steeply trom the surface, with a range of depth from four to eight inches. The spoil at the mouths of the abodes has a distinctly granular appearance, and “a lining of adhesive quality that runs the length of the shaft furnishes an example of ingenuity no less praiseworthy than is provided by the delicate workmanship of spiders that live in the hedgerow and undergrowth.”

The methods of the burrowing spiders seem to De on lines very much like those of the trap-door spiders, whose doors fit the tops of the retreats with surprising exactness. The jaws of all these spiders are furnished for digging. Particles of soil are dislodged patiently by the powerful mandibles and are carried away and deposited at a distance. In all this work, ingenious although it may be, the spiders seem to be actuated by instinct, not by forethought. Usually, a trap-door resembles so closely its surroundings that there seems to be some kind of design in

this. Experiments show that whatever decoration there may be on a door is the result of an impelling force under which the builder uses any material in the neighbourhood, without regard to the effect mc.,uced In one case, a spider whose door was removed made a new one, covered it with moss, and caused it to be as conspicuous as an oasis in a desert. In another case a spider wove into its door naginents of a scarlet fragment intentionally left by an observer close at hand.