Popular Science Monthly/Volume 1/October 1872/As Regards Spiders
|←Has our Climate Changed?||Popular Science Monthly Volume 1 October 1872 (1872)
As Regards Spiders
|Man as the Interpreter of Nature→|
" WHAT can there be interesting in that commonplace, repulsive little creature, which infests our houses, annoys us by its presence, and shocks our sense of decency with its filthy webs—in that cruel little monster, whose whole life is employed in weaving snares to entrap unwary flies; lying in wait for them in dark, damp corners of crevices, murdering them remorselessly when they are caught in its toils, and then sucking their life's-blood? The house-spider, indeed! Why, we sweep it from the very face of Nature wherever we find it, together with its chamber of horrors; and it must indeed be some strong temptation that would induce one to defile one's hands by contact with a creature the very idea of which suffices to inspire terror and disgust."
It is true that spiders are not very lovable creatures, but this is a prejudiced statement. Spiders are only repulsive as long as we are ignorant of them. If we will but stop to observe their wonderful structure and their ingenious ways, we shall quickly get rid of these foolish notions, and find that the creature will richly repay us for the time and pains of studying it. Spiders have a great deal of character, and, although very savage, they have also much in common with the vaunted heads of creation. Let us consider some of their peculiarities.
Spiders were formerly classed as insects, and they are commonly so regarded still, but this is an error. Insects have but six legs, while spiders have eight; there is a division in insects between the head and the trunk, but spiders have no separate head, the head and thorax being fused together, under the name of cephalothorax. In many kinds, body, thorax, and abdomen, are so closely merged together that their parts cannot be traced. Again, insects undergo metamorphoses or transformations in their growth, while spiders do not. They belong to a group which includes mites and scorpions, and is named the Arachnida. There are multitudes of different kinds, and they vary in dimensions from the size of a grain of sand to several inches in diameter. Some spiders are met with in all parts of the world, and some are limited to special localities; some live in the fields, and others on the water; some dwell habitually in houses, and others are driven in by cold weather; some inhabit the cellar, and others establish themselves in the corners of rooms, the angles of windows, openings in the woodwork, or chinks in the walls, and each has its special adaptations and modes of life.
Fig. 1 represents a small house-spider as seen under a magnifying-glass. It has eight eyes, simple in structure, and incapable of motion, but disposed in two rows on the top of the head, so that they enable the creature to espy its prey, from whatever quarter it may approach. Fig. 2 is this part of the animal represented still more highly magnified.
Spiders, being carnivorous, must make other creatures their prey, and they are very effectually provided with the means of doing so. No other animal is so terribly armed. Below the eyes (Fig. 1, b b) you perceive the large basal joints of the jaws, or mandibles as they are termed, with which they do their small work of butchery. Fig. 3 shows the appearance of this deadly instrument greatly magnified. "Picture to yourself a pair of huge, sharp-pointed jack-knives with extremely broad handles, the blades being so opposed to one another, that, when they are forcibly driven into an object, their pointed extremities encounter each other in the centre. Then conceive these knives to have the edges of their blades serrated with a row of fine teeth commencing near the haft, and on the handle itself five large, pointed teeth, shaped like the head of a lance, and upon which the saw-like blade can be brought to work to and fro." The large claw or horn (Fig. 3) answers to the blade, a representing its fine teeth, while b shows the five lance-like teeth in the handle against which the blade works. But, besides these mandibles, the spider possesses a smaller pair of jaws, called
the "maxillæ," which also have finely-toothed edges like deeply-cut rasps that most probably operate one against the other, to enlarge the wound made by the mandibles. This looks formidable enough, but it is not the worst. Nature has equipped the spider for very thorough work. This combination of dirks and saws is poisoned. At the basal joints of the mandibles there is a receptacle filled with a subtle venom which is conveyed through a tube (Fig. 3, d) to the pointed extremity of the blade. The moment this pierces the body of the prey, the poison is emitted, and, entering the wound, renders it fatal, probably at the same time benumbing the sensibility of the victim. The injected poison is nearly colorless, and possesses most of the properties that exist in the venom of the rattlesnake or the viper. The bite of a large spider on the back of the hand has been known to swell the whole arm, so that it was hardly recognizable as belonging to the human figure.
There is a famous spider called the tarantula, from the town of Tarentum, in Italy, where it is plentiful. It is believed by the people of that region that the bite of the tarantula produces the most extraordinary effects—a silent melancholy, and convulsive movements, which can only be cured by music, while a certain tune is needful in each particular case. No doubt an epidemic nervous disease spread among persons of both sexes in this community, but it was a kind of contagious hysteria, that had nothing to do with the tarantula. That
this malady was cured by music, and consequent dancing, is very probable. The patient having indulged in long and continuous exercise, producing violent perspiration, became exhausted, fell asleep, and awoke cured.
The legs of the spider are admirably adapted to its peculiar mode
of life. Fig. 5 represents the under surface of its body. Its eight legs are disposed in an oval upon the cephalothorax, and are long and slender, each having seven joints. They are suited for firmly grasping its prey, and, when stretched out, while the creature is watching or moving, they cause the weight of the body to be distributed over a large surface of the fragile web. All this preparation for war is not thrown away, as spiders are plucky and desperate fighters. Although consummate strategists, and availing themselves to the utmost of cunning snares, they are ever ready for an attack, and fight ferociously. Their muscular force is very great, and some of them are so tenacious
|Fig. 6.||Fig. 7.|
|Terminal Point of the Spider's Foot,
showing the Hooked Comb.
|One of the Combs, highly magnified.|
that it is difficult to make them let go their hold of the enemy that has been seized. Of the great crab-spider it is said that the obstinacy and bitterness which it exhibits in combat cease only with its life. Some of them have been seen, which, though pierced twenty times through and through, still continued to assail their adversaries without showing the least desire of escaping them by flight.
But let us proceed with the animal's structure. The long, many-jointed legs are terminated with a beautiful apparatus resembling a
|Fig. 8.||Fig. 9.|
|Last Joint of one of the Maxillary
Palpi of Male Spider.
|The same in the Female.|
comb, with a pointed hook at the extremity. These instruments are not only of service in its encounters with enemies, but they are skilfully constructed to grasp, card, disentangle, or wind its threads with the utmost facility. Nothing comparable to it for this purpose can be found among all the contrivances of our factories. Again, glancing at Fig. 5, we notice, on either side of the head, what might be mistaken for a fifth pair of shorter legs: these are the maxillary palpi, which probably correspond partially to the feelers or antennas of insects. They differ in the male and female, and the club-shaped palpi are said to serve a most remarkable physiological end in connection with generation. The palpi of the male are furnished with several hooks, and a kind of cup (Fig. 8), while those of the female taper to a point, and are armed at the extremity with a toothed comb, like those at the end of the feet, and with several long, sword-shaped hairs.
But if, at the anterior extremity of the spider, we see in miniature the most perfect enginery of destruction, at its posterior extremity there is an equally marvellous device for the work of construction. If you direct your lens to the abdominal segment, you will observe what is represented in Fig. 10. The projections there seen are called spinnerets, and are contrivances for producing the web. One pair is prominent, the remaining two pairs having the appearance of circlets (Fig. 10, ), and they are all studded over with rows of little microscopic tubes (Fig. 10, b b). From these minute tubes there exudes a glutinous substance prepared in the spider's body, which solidifies into
a fine, strong filament as soon as it is exposed to the air. The microscope has proved that every one of these almost invisible fibres is composed of hundreds of finer ones, just as a ship's cable is formed of minute hempen fibres, while the main strand is spun far more rapidly than the eye can follow the process. The strength thus secured is very great, and the line is not only strong but elastic, like an India-rubber thread. cohesion. It is a remarkable fact that the spinnerets are under the prompt control of the spider's will, so that, in dropping from a height by the rapidly-forming line, the descent can be instantaneously stopped at any point. It is equally curious that, in ascending the line, a spider winds up the superfluous cord into a ball, and has a special claw or comb inserted between the others for the purpose., the renowned microscopist, who studied this subject carefully, made some extraordinary statements in regard to the minuteness of these threads. Some spiders, he says, that are not larger than a grain of sand, spin complex cords of which it would take millions to equal in thickness one of the hairs of his beard. If we ask why the mechanism was not simplified so that the animal should pay out only a single line, the obvious reply is that the multitude of finer filaments were necessary for quick drying and the firmest
Some kinds of spiders take to ballooning or migrating from place to place through the air. For this purpose they spin those long, loose and amazingly attenuous threads called gossamer, which exert a buoyant influence by which the animal is enabled to commit itself to atmospheric currents and move from place to place, and by which it gains the partial advantage of wings.
In the construction of webs for the snaring of its prey, the resources of the spider are endless. Dr. Samuelson, from whose admirable monograph our illustrations are taken, says: "With wonderful rapidity and instinct, the spider employs these threads to weave its web, or wanders from place to place, often constructing a perfect net, to entrap its prey, upon accurate geometrical principles, in less than an hour; and, what is most remarkable of all, performing this task in what to us would be total darkness. There are many other curious and mysterious circumstances connected with these webs. The garden-spider, for instance, covers all the concentric filaments of its net, at regular intervals, with glutinous or adhesive globules, presenting under the microscope the appearance of pearls strung upon a thread, and destined to facilitate the capture of its prey."
The work of the geometrical spiders may at almost any time in the proper season be observed in the garden. As the flight of insects is mainly in an horizontal direction, the net is usually fixed in a perpendicular or somewhat oblique position to intercept them. The first thing is to enclose a space with strong lines as a kind of frame, within which the web is to be formed. It is immaterial what is the shape of this enclosed area, as the spider is aware that she can as well inscribe a circle in a triangle as in a square. But these outside lines must be strong, and so they are formed of several threads glued together and attached to various objects of support. Mr. Spence thus describes the subsequent construction: "Having completed the foundations of her snare, she proceeds to fill up the outline. Attaching a thread to one of the main lines, she walks along it, guiding it with one of her hind-feet that it may not touch in any part, and be prematurely glued, and crosses over to the opposite side, where, by applying her spinners, she firmly fixes it. To the middle of this diagonal thread, which is to form the centre of her net, she fixes a second, which, in like manner, she conveys and fastens to another part of the lines encircling the area. Her work now proceeds rapidly. During the preliminary operations she sometimes rests, as though her plan required meditation. But no sooner are the marginal lines of her net firmly stretched, and two or three radii spun from its centre, than she continues her labor so quickly and unremittingly that the eye can scarcely follow her progress. The radii, to the number of about twenty, giving the net the appearance of a wheel, are speedily finished. She then proceeds to the centre, quickly turns herself round, and pulls each thread with her feet to ascertain its strength, breaking any one that seems defective and replacing it by another. Next, she glues immediately round the centre five or six small, concentric circles, close to each other, and then four or five larger ones, each separated by a space of half an inch or more. These last serve as a sort of temporary scaffolding to walk over, and to keep the radii properly stretched while she glues to them the concentric circles that are to remain, which she now proceeds to construct. Placing herself at the circumference, and fastening her thread to the end of one of the radii, she walks up that one toward the centre, to such a distance as to draw the thread from her body of a sufficient length to reach to the next; then stepping across, and conducting the thread with one of her hind-feet, she glues it with her spinners to the point in the adjoining radius to which it is to be fixed. This process she repeats until she has filled up nearly the whole space from the circumference to the centre with concentric circles, distant from each other about the sixth of an inch. Besides the main web, the spider sometimes carries up from its edges and surface a number of single threads, often to the height of many feet, joining and crossing each other in various directions. Across these lines, which may be compared to the tackling of a ship, flies seem unable to avoid directing their flight. The certain consequence is that, in striking against these ropes, they become slightly entangled, and, in their endeavors to disengage themselves, rarely escape being precipitated into the net spread underneath for their reception, where their doom is inevitable."
The weaving-spider that is found in houses having selected a suitable site, in the same way forms first the margin or selvage of her web. From these she draws other threads, the spaces between which she fills up by running from one to the other, and connecting them by new lines, until the gauze-like texture is formed. The spider seems to be aware that she is no beauty, and had better conceal herself; so she constructs a small silken apartment, completely hidden from view, in which she lies in wait for her victims. But as this is often at a distance from the net, and entirely out of sight of it, how is she to know when an insect is caught? To meet this emergency, she spins several threads from the edge of the net to that of her hole, which answers as a telegraph by its vibrations, and is a railroad over which she can pass to secure it.
In their vital physiology spiders are quite as wonderful as in their other characters. We have said that they do not undergo metamorphoses, like insects, but the common household spider, which we have figured (Tegenaria domestica), changes its integument, or skin, nine times before arriving at maturity, once in the cocoon and eight times after quitting it. If they lose a leg it is quickly reproduced, and this may take place half a dozen times in succession. Mr. Wood says, indeed, that "the harvest-spider seems to set little store by its legs, and will throw off one or two of them on the slightest provocation. Indeed, it is not very easy to find a harvest-spider with all its limbs complete; and, if such a being should be captured, it is nearly certain to shed a leg or two during the process. It appears to be totally indifferent to legs, and will walk off quite briskly with only half its usual complement of limbs. I have even known this arachnid to be deprived of all its legs save one, and to edge itself along by this solitary member, in a manner sufficiently ludicrous. The cast legs contain much irritability, and, even after they have been severed from the body, continue to bend and straighten themselves for some little time." The household spider above referred to lives four years; and the female, after one impregnation, is capable of producing nine sets of prolific eggs in succession, more than two years elapsing before all are deposited.
Morally, the spider has a bad reputation, and is the subject of many vile epithets; but, when compared with its accusers, it presents by no means a bad case. The Arachnidian ethics are in many respects strikingly coincident with more ambitious systems. The spider practises the virtues of industry, patience, and perseverance, under difficulties. The female is an affectionate parent, and very fond of her young. About June the garden-spider makes up her little packet of eggs, and encloses them in a snow-white silken envelope, and carries it about with her wherever she goes. If it is forcibly removed, she remains on the spot, hunting in every direction, and evidently in great distress; and if the white ball be laid near her she soon spies it, darts at it almost fiercely, and carries it off. "When the time comes for the little spiders to make their appearance in the world, the mother tears open the envelope, and so aids her young to escape. As soon as they are fairly out of the egg, they transfer themselves to the body of their parent, where they cling in such numbers that she is hardly visible under her swarming brood. They remain with their mother through the winter, and in the following spring the bonds of mutual affection are loosened, and the young disperse to seek their own living." If the spider is a skilful hunter and an ingenious trapper, so are the heroes of many novels; but the animal has not yet been known to indulge its predaceous practices in the way of mere wanton sport. It is merciless and cruel, like inquisitors and tyrants, but does not perpetrate its cruelties on the ground of difference of opinions. It is moved by self-interest, the alleged basis of all political economy. The spider "must live, you know," and it is a maxim with it to "look out for number one;" while it has a high appreciation of the advantages of "corner lots," but in all this it is by no means singular. Besides, the spider contributes its share to the general weal. What would this world come to, if the flies could have their own way in it without let or hindrance? Killing flies is a necessary and righteous thing, and, as it is jointly undertaken by men, women, and spiders, for purposes of common beneficence, each should have an aliquot share of the honor. The spider, as we have seen, is also courageous and soldierly. He is fond of war, and, having taken a position, is very apt to "fight it out on that line," or system of lines, till crowned with victory. But it invests war with no sentiment of "glory," does not dress it up with gilt and feathers, nor use its passions as political stock-in-trade. Sundry misanthropes have claimed for the spider a standard of virtue higher than the human, as witness the following effusion:
"Ingenious insect, but of ruthless mould,
This is tolerable poetry, but very poor science. Truth compels us to drag the spider down to the human level—it does kill its own kind. Had it not been for this habit, men would have long ago enslaved the spiders to the silk-business. It is again charged that the spider is a cannibal, and, having killed bis fellow-citizens, proceeds to devour them. But here, again, the spider can claim no originality, and is but an humble imitator of the lords of creation. It has, moreover, been accused of practising murder under very delicate circumstances, when its mind should only be occupied with tender feelings. It is true that love and courtship in the Arachnidian world are apt to be tragical. These creatures are quite too literal in their construction of the phrases, "You will kill me with your coldness," "Love me or I die;" but, in a higher sphere, does not love often become a bloody business of suicide and murder? Yet to the honor of humanity be it said, spiders do one thing which our sort do not: they kill their lovers, and then eat them up on the spot. In many species the male is much smaller than the female, and with these courtship is perilous. The female of the garden-spider is a perfect Amazon, and, when she happens to object to the attentions of her intended spouse, he has to fly for his life; a feat which he generally performs by flinging himself like lightning out of the web, and lowering himself quickly to the earth by his silken ladder.
We here reach the perplexing question of "female rights," but decline to pursue it. "The Poet at the Breakfast-Table" has just bravely taken it up from this point of view, recommending the reformatory ladies to organize "Arachnoid Associations," with "Spinsters and Spiders" for a motto, and we leave the subject trustingly in his hands.