WAYS OF THE WILD.

Auckland Star, Volume LXI, Issue 69, 22 March 1930, Page 1 (Supplement)

WAYS OF THE WILD.

A NATURALIST'S NOTEBOOK. SPIDERS' WEBS. (By A. T. PYCROFT.) Before describing one type of the manv beautiful webs made by spiders, some of which are marvels ol architec - tural skill, it should be understood that spiders vary greatly in their spinning powers. Some only use their silk 1"r spinning a cocoon to protect their eggs, while others employ it to make snares and retreats, or to bind up their prey, and others, again, to anchor themselves to spots to which they may wish to return. All these functions arc performed by the silk glands of the orb weavers, those spiders which make wheel-like webs, and hence it is with them that the spinning organs have, attained their greatest perfection. ll we examine the large garden spider ve find that the glands occupy the entire floor of the abdomen, and consist of t about six hundred. This great number of orifices from which silk may he emitted has given rise, to the popular belief that, fine as the spider's line i-. it. is woven of hundreds of strands. This is an entire misconception. Within the body of the animal the silk is in the form of a gummy fluid, and this being emitted in exceedingly line strands solidifies as it meets the air. It cannot, be shot out to any distance, but the animal usually draws it out by its hind legs, or attaches it to a spot and moveaway by walking, or allowing itself to drop. It has some power of cheeking the output, and can stop at will at any point of its descent, but the muscles which close the openings are weak, and by steady winding a student secured as much as a hundred yards of silk as it was reeled out. The flow was then interrupted by the spider rubbing its spinnerets together and breaking the thread. The Circular Snare. This familiar object is sometimes spoken of as the orb web or wheel web. The accuracy and regularit; of form exhibited by" these snares has caused their architects to be sometimes called the geometric spiders. The ingenuity displayed by them has always excited the admiration of the naturalist, and this is increased on closer observation, for the snares are in reality even more complex than they appear at first sight. The first care of the spider is to lay down the foundation threads which are to form the boundary lines of its net. If the animal can reach the necessary points of attachment by walking along intervening surfaces the matter is comparatively simple. The spinnerets are separated and rubbed against one of the points selected, and the spider walks away, trailing behind it a thread which it keeps free from neighbouring objects by the action of one of its hind legs. On reaching another desirable point of attachment the line is made taut and fixed by again rubbing the spinnerets against it. By a repetition of this proceeding a framework is presently constructed, within which the wheel or orb will ultimately be formed. The process of fixing and drawing out a line can be watched by the aid of a lens. It will be seen that a large number of very fine lines, starting from the point of attachment, seem to merge into a single line as the spider moves away. This has given rise to the prevalent and very natural idea that the ordinary spider's line is formed or woven of many strands. This, however, is not the «<se, for the fine attachment lines are nor; continued into the main thread, but only serve to anchor it to the starting point.

How a Stream is Bridged. Everyone must have noticed that orb» webs frequently bridge over gulfs that are clearly quite impassable to the spider in the ordinary way. The makers of these webs, which cannot swim, often span streams, or their webs are stretched between objects unattainable from each other on foot 'except by a very long and roundabout journey. In such cases the spiders have recourse to the aid of the wind. With air currents to aid it, silken streamers will at length find their way across the water and become entangled in some neighbouring object. When this lias happened the spider hauls the new line taut, and tests its strength by gently pulling at it, and if the result is satisfactory it proceeds to walk across, hand over hand, in an inverted position, carrying with it a second line to strengthen the first. Some of these bridge lines made by the great orb weavers of tropical countries span streams several yards in width. Two stout bridge lines thus constructed will form the upper and lower boundaries of the net. The lateral limits are easily formed by cross-lines between them at a convenient distance apart. Two such cross-lines give with the bridge lilies, an irregular four-sided figure within which to stretch the snare. Attention is first paid to the lines radiating from the centre. As these are extended the spider carefully attaches them where they intersect by a small flossy mass of silk, and this central point or hub becomes the basis of its subsequent operations. New radial lines arc added, and almost every time the spider reaches the centre it slowly revolves, uniting the radial lines afresh at their point of junction and increasing the strength and complexity of the hub. The whole structure is also stretched by bracing the framework at additional, points so that it loses its four-sided form and becomes polygonal. The hub is next strengthened by a few turns of spiral thread, which serve to bind more firmly the spokes of the wheel. Setting the Snare. The most important part of the work is still to be performed. The lines hitherto laid down are perfectly dry and freo from viscidity, so that an entangled insect would easily be able to free itself. A viscid spiral line remains to be spun and the snare will be complete. The proceeding consists in drawing out from the spinnerets with one or both of its hind legs successive lengths of a higlilyelastic line coated with a viscid substance. The line is stretched just at the moment of fixing to a radius and then let go with a snap, which causes the viscid substance to break up into globules of sticky matter which holds the prey iii the same way that bird lime holds h bird. The snaro is now complete, and the proprietress takes up her position either in the centre thereof or in some retreat close at hand and connected with the hub by special lines. It is mainly by the sense of touch that the spider presently becomes aware that an insect is struggling in the net. She immediately rushes to the spot and suits_ ie. action to the emergency. _ The visck matter on the spiral line dries up aitt some hours, so that, pen j ; has not been destroyed b.y m*c.. s ami stress of weather, tins portion o. .t -i,,, be frequently; renewed.