THE TRAP-DOOR SPIDER

Sun (Auckland), Volume 1, Issue 41, 11 May 1927, Page 14

THE TRAP-DOOR SPIDER

Imagine a trap-door spider at work. She begins by tunnelling into the ground, generally into a bank. With her powerful jaws she excavates soil and carries out every grain she loosens. As the gallery grows wider and deeper she clothes the walls with silk of her own spinning. Perhaps there are patches here and there in which the loose soil is apt to cave in, and in a twinkling a shield is woven and glued to the sticky part. Then she must think of the enemy at the gate. She rapidly throws a covering of silk completely over the opening to her house, then she carries quantities of soil and lays it on the web she has woven. Over that she lays another coverlet of silk, then lays on more soil or gravel, and covers that with more silk, until, with these alternate layers of silk and gravel or other things, she has wrought a stout and formidable portal. But the entire entrance is not only covered: it is sealed. She has built herself out. But it is only for a few moments. With her strong jaws she cuts the silk of the door for two-thirds of the way round; the remaining third she leaves uncut. That is the hinge of the door, tough, enduring, the first known hinge in the history of the world. She can raise the door with her jaws now, for it comes open easily, turning back on that marvellous hinge of silk, and in she pops. Strands of silk hang down from the underside of the door, and she links these up with more silk, weaves a sheet and covers the walls of her passage with patchwork. Much has been written about trapdoor spiders, but the great authority is Mr. Traherne Moggridge, and we will adopt the names he has given to the doors. The door we have described he calls the cork door, because it fits into the gallery like a cork. The cork door is bevelled and fits into a bevelled seating, like the valve of a motorengine. That is an exquisite refinement of spider work, for it makes the closing much more accurate and also watertight. The door has its greatest circumference on the outside; its nar rowest on the inner side. Think for a moment of the perfection of that bit of workmanship, of the fitting of the bevelled door into its bevelled receptacle. What untaught man could do it? The savage leaves a rough hole, low down, for a door to his hut and when he comes out in the morning, creeping on hands and knees, head downward, the hyena may be there •lying in wait. But the trap-door spider knows a better way. When she comes out to catch her food the spider pushes open her door from inside. Its weight and the elasticity of the hinge are enough to close it again. If she wants it open she fastens it back with a strand of silk fixed to some object near. Otherwise it pops back perfectly into place. Now comes what Mr. Moggridge calls the wafer trap-door, much thinner than the cork door and therefore not so strong. But the spider is not a worse builder for that. If an enemy attacks the cork door the spider runs up the gallery and, with her strong jaws and legs, pulls with all her might to hold it shut, clinging with some of her legs to the walls and with others to the inner side of the door. A wafer door is more easily penetrated, but when an enemy insect-eater gets some way down the tube, lo! there is that unexpected second door. The door opens downward, so this time the spider pushes. She grips the sides of the walls and with her back to the door pushes as we push with our shoulders at a door which is being forced against us. Splendid, is it not 17 But there is a second type of wafer door, leading to a long gallery of the Y shape, and here we come to the very pinnacle of spider science. Down from the surface comes the main gallery Half-way down is a blind gallery, rising toward the surface but not quite to the top. Now, at the junction of the legs of the' Y is a second trapdoor. It moves on a silken hinge. Ordinarily it is in such a position that it can be pushed upward so as to rest diagonally across the main tube and block it. but it is not meant for that alone. The builder seems to recognise the possibility of being. overwhelmed by force, so this second door can be pulled tight across the entrance to the second tube, the right leg of the Y. If an enemy should break in he may be detained first of all by the door placed across the main tube, but if he should advance beyond that defence the spider can hop up into the second tube and slam the door behind it. In that case the door, buried in the silk of the wall, is indistinguishable from it. It is safe and tight. The spider can remain there if she chooses, or, while the enemy is blundering down the recesses of the deep main tube, she can open her door, skip lightly up the main tube and flee into the open. What boy will refuse after this to touch his cap to the spider? Is there anything more perfect than this in the whole story of Nature? Of course, we remember the glories of the beehive, the engineering of the beaver in controlling rivers and building his dams, but they do not match the work of the trap-door spider. The planning and execution are beyond praise, for the spider which does it is an artist in camouflage. After she has established that wonderful front door she will actually carry moss and plant over it, so that vegetation grows there and hides it. Or she will carry leaves and twigs and bind them with silk into an obliterating screen. In the case of the wafer door the material is too drv for vegetation to grow, so the spider carries earth or leaves to it as a covering.