An Engineering Spider

An African spider that knows how to raise heavy weights by an application of what we shall call engineering methods, is described in L'Echo de Paris, by a contributor who signs himself 'Onyx.' When we see enormous megalithic monuments, says this writer, or the cyclopean structures of certain primitive peoples, we ask ourselves, in astonishment, how men who were ignorant of all the resources of mechanics could have transported such great masses of stone. The explanation evidently lies in the union and coordination of a great number of individual efforts, at epochs when the problem of manual labor presented no difficulty. How much more extraordinary should appear to us the work of a small spider, who, relying only upon its own strength, succeeds in suspending a structure that sometimes weighs thirty-five times as much as itself. We read further:

"This ponderous dwelling, which the spider hangs to the branches of shrubs, is nothing but nothing but the shell of a mollusk. It is well known that these shells, which are houses built after a fashion taught to the mollusks by nature, may, after the death of the legitimate proprietor, serve as dwellings or nests for other creatures. The hermit crab, especially, lives constantly in one of these natural shelters, while certain insects install their own progeny therein. The spider in question, which Mr. R. Decary, one of our colonial administrators, has discovered and studied in the extreme south of Madagascar, uses snail-shells at once as a dwelling and a nest. The female spends her whole life in this retreat; she lays her eggs there and the young are born shortly after. The male is a vagabond, without fixt home, who abandons to his spouse the efforts of installation and the austere joys of her hermit existence

"As we said above, the originality of this hermit's cell consists in the fact that it is balanced between heaven and earth. It is found hanging from the branches of shrubs, at a height that may be as great as sixteen inches above the ground. It is held to the branch by silken threads six to eight inches long, fastened to the point of the shell, which has been previously furnished with a solid sheath. This also serves as a silk curtain which closes the entrance of the house, that is to say, the opening of the shell, which is turned downward.

"Now that we know the facts, we have stated the problem. How can the little creature, which is hardly half an inch long, raise to such a great relative height a mass thirty-five times as heavy as herself? Imagine a man hoisting, with his unaided arms, by means of a cable a block weighing over two tons to a height of 350 feet! This is practically what the spider does.

"How does she go about it? The feat is very difficult to observe on the spot, for the work is always done at night, and bright light interrupts it. Mr. Decary nevertheless succeeded in avoiding this difficulty and raised one of these spiders in captivity. He saw it first attach its cable to the shell; then it seemed to him that the spider hoisted its house by hauling on the thread with its claws.

"But would such a method suffice to explain the exploits performed by the spider in a state of nature? It would not seem so. So Mr. L. Faye, of the Museum, who has studied the anatomy of this species, suggests the use of another process, less fatiguing and much more ingenious.

"Various spiders, notably the Theridion, are accustomed to decorate the outside of their cocoons with small pebbles, and the remarkable way in which they raise these materials has been observed. They descend toward the ground, spinning a silken thread fastened to the cocoon, attach the other end to the tiny pebble, and go up again, spinning a second thread. The threads in drying, contract and raise the stone somewhat; the creature then repeats the same tactics, each time gaining a few fractions of an inch and without any great exertion of strength the stone, little by little, reaches its destination. It is quite probable that the Madagascar spider uses some similar scheme, which resembles the moistening of the ropes sometimes used to readjust a scaffolding.

"Thus, to raise heavy objects, spiders have learned how to profit by a physical characteristic of the threads that they secrete. In our world of men, that would be called a mechanical invention, but when it is done by insects we describe these wonders of the intellect by using the somewhat vague name of 'instinct.' Nevertheless, is this judicious utilization of a force of nature so very different from the scientific applications of which we are so proud?"



Other spiders


Other arachnids

From: Anonymous. The Literary Digest, October 23, 1926, p. 23.