CHAPTER III.. Manufacture of Silk by Spiders.

MANUFACTURE OF SILK BY SPIDERS.

Our history of the silk manufacture among insects would be incomplete without a notice of the labours of spiders. Not only do these insects produce filmy webs to entrap their prey, but they also spin, for the protection of their eggs, a bag not much unlike the cocoon of the silkworm. At the beginning of the last century a method was discovered of procuring silk from these spiders’ bags, and of making it into several useful articles. The experiments took place in France, and it was there discovered that two species of spider in particular produced strong and beautiful silk, capable of being usefully employed. The structure of these insects was closely examined by the celebrated naturalist Réaumur, and he found that the silk is spun from five papillæ, or small nipples, placed in the hinder part of the body; these serve the purpose of so many wire-drawing irons, to mould a gummy liquor, which dries as it is drawn out and exposed to the air.

SPINNING APPARATUS OF THE SPIDER.

(Greatly magnified.) ]

On pressing the body of a spider, the liquor flows into these nipples, by applying the finger against which, distinct threads may be drawn out through the numerous openings; and, what is very astonishing, every separate thread is made up of innumerable smaller threads, so that Réaumur thought himself far within the limits of the truth when he stated that each of the five nipples supplied one thousand separate fibres, in which case the slender filament of the spider’s nest must be made up of five thousand fibres. By applying the whole, or a part, of this apparatus to her work, the spider can make the thread stout or fine at pleasure: thus the webs for entrapping flies are very slight and fragile; but the nest for securing the eggs is much stronger, to afford them shelter from the cold. The threads are wound loosely round the eggs in a shape similar to that of the silkworm’s cocoon. The colour of the silk is generally grey, becoming blackish on exposure to the air: sometimes it is pale yellow, and also of very fine quality; but this is the production of comparatively rare species, which could not be depended on for the purposes of manufacture. A spider’s nest preserved by the writer during the last winter was of a beautiful yellow, almost approaching that of the cocoon of the silkworm. As spring approached it increased in bulk and became rather paler, until at last a dark appearance in the centre betokened the bursting of the eggs. At the present time (April 10th) ninety-six small yellow-bodied spiders have come forth, and are actively engaged in weaving their delicate webs across the glass which contains them. A muslin cover admits air to the interior, and these minute insects appear perfectly healthy although deprived of their natural food. Some sugar was placed in the glass, but they do not appear to have consumed any of it, although some of them have been hatched for more than a fortnight. From the appearance of the nest, more of these spiders yet remain to be hatched.

In the French experiments, spiders’ nests in large quantities were collected from the trunks of trees, corners of windows and vaults, and eaves of houses at the time above mentioned, and from these a new kind of silk was obtained by M. Bon, who declared it to be in no respect inferior to that of the silkworm. It was afterwards proved that he was greatly mistaken in this respect; yet the spiders’ silk readily took all kinds of dyes, and was actually wrought into stockings and gloves, specimens of which were presented by M. Bon to the Royal Academy of Paris, and also to the Royal Society of London. His method of preparing the silk was as follows:—

Twelve or thirteen ounces of the bags were beaten with the hand, or by a stick, until they were entirely free from dust. They were then washed in warm water, which was frequently changed, until it was no longer discoloured by the bags. They were next steeped in a large quantity of water, wherein soap, saltpetre, and gum-arabic had been dissolved. The whole was then set to boil over a gentle fire for three hours. Lastly, the bags were rinsed in clear warm water, and set out to dry. They were then fit for the operation of carding, which was performed with very fine cards, and thus silk of a peculiar ash colour was obtained, which was spun without difficulty.

SPIDER’S NEST ATTACHED TO A FLAT SURFACE. ]

SPIDER’S NEST LAID OPEN. ]

The great obstacle which prevented the establishment of any considerable manufacture from these spiders’ bags, was the difficulty of obtaining them in sufficient abundance; but M. Bon, who was enthusiastic respecting the value of his discovery, fancied that he could easily overcome this obstacle, and at first his efforts appeared remarkably successful. He formed a large spider establishment, which, for a time, was very prosperous. Having ordered all the short-legged spiders (which are the most industrious spinners) to be collected for him by persons employed for the purpose, he enclosed them in paper boxes, with pin-holes pricked in them to admit the air to the prisoners. The insects were regularly fed with flies, and prospered well on their diet. In due time most of them laid their eggs, and spun their silken bags. M. Bon affirmed that each female produced from six to seven hundred eggs, whereas the silkworm moth lays only about one hundred. He also stated, that out of seven hundred or eight hundred young spiders which he kept, scarcely one died in a year; while of one hundred silkworms, not forty lived to form their cocoons.

These favourable statements led the Royal Academy of Paris to take the subject into consideration, and Réaumur was appointed to inquire into the merits of the new scheme. This careful inquirer found many serious obstacles in the way of such establishments. The fierceness of spiders, and their propensity to destroy each other, were noticed as unfitting them to be bred and reared together. On distributing about five thousand spiders in cells, in companies of about fifty or a hundred, it was found that the larger spiders quickly killed and ate the smaller, until there were only one or two occupiers of each cell. The silk of the spider was also found inferior in lustre and strength to that of the silkworm, and had the disadvantage of being incapable of winding off the ball, but must necessarily be carded.

GARDEN SPIDER—(Natural Size.) ]

Indeed, it could require no very great consideration to decide, that spiders’ silk, when compared with that of the silkworm, was vastly inferior for manufacturing purposes, though employed in many useful and highly ingenious ways by the insect itself. A few of these we must not omit to notice. Every one must have seen the common garden spider (Epeira diadema) suspended by its silken rope, or forming its beautiful web; but every one is not aware that that silken rope is made up of a multiplicity of threads, and that when the spider attaches the rope to any object by pressing her spinneret against it, she spreads out these threads over an area of some diameter, thus securing a much greater degree of strength than could be gained by merely fixing her thread to one point. This contrivance may be seen best when the threads are attached to a black object. Under the microscope they appear thus:—

SPIDER’S METHOD OF ATTACHING HER THREAD. ]

The uses of silk in the webs and nests of common spiders are too obvious to be dwelt on, but there is a most clever and surprising adaptation of the same material by several foreign species of spider which must be briefly stated. In the Ionian islands, and also in the West Indies, there are found certain spiders, commonly known as trap-door spiders, which make a cylindrical nest in the earth, and cover the entrance with a door of their own construction, framed of alternate layers of silk and earth, and fastened to the opening by a hinge of stout silk. These spiders also line their nests throughout with numerous layers of silken web to the thickness of stout cartridge paper, and finish it with the greatest care. This beautiful lining is yet further strengthened in particular parts, where the nest is likely to be exposed to danger. But the greatest amount of skill and care is bestowed upon the trap-door and its silken hinge. This door is about the eighth of an inch thick, rough on the outside, not much unlike an oyster shell, which it also resembles in being thick and strong near the hinge, but thinner towards the circumference. The breadth of this hinge is various, but sometimes it is very considerable, as shown in the accompanying figure. It also possesses great elastic force, so that on being opened, it closes again of itself. This is principally accomplished by a fold or doubling of the web, at each end of the hinge, which permits the door to be opened nearly to a right angle with the aperture, but no farther, unless violence be used. The under side of the door is perfectly smooth and firm, being shaped so as to fit accurately, and yet to offer no resistance when pushed open by the insect.

TRAP-DOOR SPIDER. ]

NEST OF TRAP-DOOR SPIDER. ]

TRAP-DOOR OPENING BY A LEVER. ]

As might be expected, there are varieties in the shape and size of these nests. Some specimens found in the island of Zante had the silken layers of the lid extended into a sort of handle or lever just above the hinge, on pressing which in ever so slight a degree the trap-door opened. From this it would appear that the entrance to such a nest could be effected as easily by the enemies of the spider as by the spider itself: this, however, is not the case; for repeated observation has shown that the spider keeps guard at the entrance, and actually holds the door with her fore feet and palpi, while the hinder feet are extended down the side of the nest, and the mandibles are thrust into the opposite side near the door. By this means the insect gets such power as to resist with considerable force the opening of the door. If it be asked how this is known, we are able to refer to the experiments of careful observers, who extracted a number of nests from the ground, and opening them at the lower end, looked up, and saw the spider so occupied. A sectional view of the nest will show that the curved form of the cover, and the shape of the side walls, must favour this method of keeping the door shut. In some cases, small hollows were formed round the interior edge of the lid, into which the spider thrust its feet when keeping guard. It is a curious fact, that when several of these spiders enclosed in their nests were kept as a matter of curiosity in a box of earth, and the doors frequently opened to examine their proceedings, one or two of them, as if wearied at these repeated interruptions, effectually closed their doors by weaving a piece of silken tapestry, which was spread over the interior of the opening, and rounded like the inside of a thimble. This was so strongly attached to the door and to the side walls, that no opening could be made without destroying the nest.

SECTION OF NEST. ]

It was long a matter of surprise to the observer to find, that in the case of some nests, and not of others, there was a trap-door at the bottom as well as at the top of the nest: this was at last explained by the following fact. A spider’s nest, which was accidentally broken off in being extracted from the ground, was purposely restored to the earth in a reversed position, with the trap-door downwards, and the broken and exposed part level with the surface. The spider immediately set to work to make a new door over the broken part, and finished it with as much completeness as the other. Doubtless, then, those nests which were provided with two doors were such as had been upset and broken. This is the more likely because in Zante, where such nests were found, the earth is annually dug up round the roots of the olive tree, a favourite nesting place of these trap-door spiders.

NEST WITH TWO OPENINGS. ]

We must not omit to mention, that in some parts of South America, especially in Paraguay, there is a spider which forms a spherical cocoon for its eggs, an inch in diameter, of a yellow silk, which the inhabitants spin on account of the permanency of the colour. It must also be observed that the silk of spiders is useful to the astronomer, who employs the strongest thread (the one, namely, which supports the web) for the divisions of the micrometer. By its ductility, this thread acquires about a fifth of its ordinary length.

WHITE WAX INSECT OF CHINA. ]