by J. H. Emerton
One of the most curious habits of spiders is that of flying, as it is often called. This has no resemblance to the flight of birds or butterflies, for spiders have no wings nor any organs which could answer the purpose of wings. Their ability to rise in the atmosphere depends entirely upon currents of air acting upon their bodies or upon threads of cobweb attached to them. By this means they are blown about like the down of thistles or any light objects, rising sometimes to a great height and again, upon a change of weather, falling, often far from the place whence they rose.
In the autumn of 1870 I received a letter from an officer on one of the United States vessels, in which he stated hat one day while at anchor near Montevideo, after a strong wind, the rigging was filled with cobwebs, and little spiders dropped down on all parts of the deck.
Mr. Darwin, when in the same region during the voyage of the Beagle, several times noticed that the same occurrence. He says in his narrative of that voyage: *--
"On several occasions, when the vessel has been within the mouth of the Plata, the rigging has been coated with the web of the gossamer spider. One day (November 1st, 1832) I paid particular attention to the phenomenon. The weather had been fine and clear, and in the morning the air was full of patches of the flocculent web, as on an autumnal day in England. The ship was sixty mils from the land, in the direction of a steady though light breeze. Vast numbers of a small spider, about one-tenth of an inch in length, and of a dusky red color, were attached to the webs. There must have been, I should suppose, some thousands on the ship. The little spider, when first coming in contact with the rigging, was always seated on a single thread, and not on the flocculent mass. The latter seemed merely to be produced by the entanglement of the single threads. The spiders were all of one species, but of both sexes, together with young ones........ While watching some that were suspended by a single thread, I several times observed that the slightest breath of air bore them away out of sight, in a horizontal line. On another occasion (Nov. 25th) under similar circumstances, I repeatedly observed the same kind of small spider, either when placed, or having crawled, on some little eminence, elevate its abdomen, send forth a thread, and then sail away in a lateral course, but with a rapidity that was quite unaccountable. I thought I could perceive that the spider, before performing the above preparatory steps, connected its legs together with the most delicate threads, but I am not sure whether this observation is correct.
"One day at Santa Fe I had a better opportunity of observing similar facts. A spider, which was about three-tenths of an inch in length, and which, in its general appearance, resembled a Citi-grade (therefore quite different from the gossamer spider), while standing on the summit of a post, darted forth four or five threads from its spinners. These, glittering in the sunshine, might be compared to rays of light. They were not, however, straight, but in undulations like a film of silk blown by the wind. They were more than a yard in length and diverged in an ascending direction from the orifices. The spider then suddenly let go its hold and was quickly borne out of sight. The day was hot and apparently quite calm; yet under such circumstances the atmosphere can never be so tranquil as not to affect a vane so delicate as the thread of a spider's web. If during a warm day we look either at the shadow of any object cast on a bank, or over a level plain, at a distant landmark, the effect of an ascending current of heated air will almost always be evident, and this probably would be sufficient to carry with it so light an object and as the little spider on its thread."
[* Journal of the Voyage of the Beagle, p. 187}
In Temple's Travels in Peru * it is mentioned that , when sailing up the river Plate, "the rigging of the ship, from top to bottom, was literally covered with long, fine cobwebs that had been blown off the shore, having attached to them their insect manufacturers, who dispersed themselves in thousands over the deck."
Such showers of cobwebs are common in Europe, especially in the autumn. They are said to be usually preceded by a great quantity of web upon the ground, which afterwards rises, and when the wind changes, or the sun begins to go down, falls again.
Mr. Blackwall, ** who has devoted many years to the study of English spiders, gives the following interesting account of one of these showers of gossamer:--
[*Temple's Travels in Peru, Vol. I, p. 49}
[**Researches in Natural History 1832. Linnaean Transactions, Vol. XV.]
"A little before noon on the 1st of October, 1826, which was a remarkably calm, sunny day, the thermometer in the shade ranging from 55 degrees to 64 degrees, I observed that the fields and hedges in the neighborhood of Manchester were covered over, by the united labors of a multitude of spiders, with a profusion of fine glossy lines, intersecting one another at every angle and forming a confused kind of network. So extremely numerous were these slender filaments, that in walking across a small pasture, my feet and ankles were thickly coated with them. It was evident, however, notwithstanding their great abundance, that they must have ben produced in a very short space of time, as early in the morning they were not sufficiently conspicuous to attract my notice, and on the 30th of September they could not have existed at all; for, on referring to my meteorological journal, I find that a strong gale from the south prevailed during the greater part of the day. A circumstance so extraordinary could not fail to excite curiosity; but what more particularly arrested my attention was the ascent of an amazing quantity of webs of an irregular, complicated structure, resembling raveled silk of the finest quality and clearest white. They were of various shapes and dimensions, some of the longest measuring upwards of five feet in length and several inches in breadth in the widest part; while others were almost as broad as long, presenting an area of a few square inches only. These webs, it was quickly perceived, were not formed in the air, as is generally believed, but at the earth's surface. The lines of which they were composed, being brought into contact by the mechanical action of gentle airs, adhered together till, by continual additions, they were accumulated into flakes or masses of considerable magnitude, on which the ascending current, occasioned by the rarefaction of the air contiguous to the heated ground, acted with so much force as to separate them from the objects to which they were attached, raising them into the atmosphere to a perpendicular height of at least several hundred feet. I collected a number of those webs about midday, as they rose, and again in the afternoon, when the upward current had ceased to support them, and they were falling; but scarcely one in twenty contained a spider, though on minute inspection, I found small winged insects, chiefly aphides, entangled in most of them.
"From contemplating this unusual display of gossamer, my thoughts were naturally directed to the animals which produced it; and the countless myriads in which they swarmed created almost as much surprise as the singular occupation that engrossed them. Apparently actuated by the same impulse, all were intent upon traversing the region of air; accordingly, after gaining the summits of various objects, as blades of grass, stubble, rails, gates, etc., by the slow and laborious process of climbing, they raised themselves still higher by straightening their limbs, and elevating the abdomen by bringing it from the usual horizontal position into one almost perpendicular, they emitted from their spinning apparatus a small quantity of the glutinous secretion with which they fabricate their silken tissues. This viscid substance being drawn out by the ascending current of rarefied air into fine lines several feet in length, was carried upwards, until the spiders, feeling themselves acted upon with sufficient force in that direction, quitted their hold of the objects on which they stood, and commenced their journey by mounting aloft. Whenever the lines became inadequate to the purpose for which they were intended, by adhering to any fixed object, they were immediately detached from the spinners by means of the last pair of legs and became converted into terrestrial gossamer, and the proceeding just described was repeated."
I do not know of any published account of similar flights of cobwebs in this country, but on almost any fine morning in summer the grass and shrubs may be found covered with threads connecting the extremities of the twigs and leaves in every direction, and floating horizontally from them sometimes to a distance of several yards. I have often seen the short grass in the Salem pasture so covered that ever leaf seemed to have several threads passing from it. One morning in June, 1868, I noticed some little spiders about one tenth of an inch long rambling about on the top of a low fence partly shaded by horse-chestnuts and apple-trees. At intervals they would stop, raise the back part of their bodies,
At another time, on one of the first warm days in March, I saw a little crab-spider running about on the ends of a barberry bush and dropping from twig to twig until it hung from the most projecting branch by a thread about a foot long. It swung back and forth for some minutes when a gust of wind blew it away so quickly that I could not follow it with my eyes. It had, however, spun a thread as it went which passed from the bush to a juniper about six feet off.
Mr. R. P. Whitfield of Albany, N. Y., tells me that once when passing through a field of oat stubble on a warm day in the autumn, he observed great numbers of threads floating upwards in the air, the lower extremity being attached to the upper ends of the stubble, and on examining some of the stalks he found numbers of small spiders busily running up and down them. When a suitable place was found the spider would attach a thread to the upper end of the stalk and then descend one or two inches and return, allowing the air to carry upward the loose thread. At the same time it elevated its abdomen and the current, acting on the loop already formed, drew out the thread from the spinnerets until a sufficient quantity had passed, when it broke off the end attached to the stalk and floated away with the web. In this way he observed several individuals ascend. At the time there was no perceptible current in the atmosphere except the upward current caused by rarefaction.
In the autumn of 1865, in Northwestern Iowa, passing along the smooth surface of the river in a boat, he observed something crossing the river with a skipping motion, striking the surface of the water at irregular intervals. Looking about he saw that the same thing was taking place at other points. Upon intercepting one, which he had watched almost from the opposite bank, he found it to be a small spider (Attus), from the abdomen of which threads of web extended several feet into the air, by which it was floated along. As it crossed the water, the air being cooler, it had descended, allowing the spider to touch the surface of the river.
To account for the ascent of threads and spiders various theories have been proposed. It was formerly supposed that the threads were thrown out from the spider as water is from a syringe, independently of any outside force, and that the threads were afterwards blown into the air carrying the spider with them.
Some have thought that the spiders actually flew in the air without help from webs or from the wind, using their legs as wings. *
Mr. Murray ** believed that a spider could shoot its threads in any direction without reference to the wind. He says: --
"Contrary to the assertion that 'spiders have no power of propelling their webs without assistance from the wind,' I fearlessly assert that they can do so in an atmosphere in which the very leaf of the aspen remains motionless; and although their char Volant obeys the direction of the breeze, this simple fact proves nothing in favor of the opinion of Mr. Blackwall. The aeronautic spider can propel its threads both horizontally and vertically and at all relative angles, in motionless air, and in an atmosphere agitated by winds; nay, more, the aerial traveler can even dart its thread, to use a nautical phrase, in the 'wind's eye.' My opinion and observations are based on many hundreds of experiments. On favorable occasions I am constantly extending their amount, and as often do I find my deductions supported, namely, that the entire phenomena are electrical. In clear, fine weather the air is invariably positive; and it is precisely in such weather that the aeronautic spider makes its ascent most easily and rapidly, whether it be summer or winter. I have often seen this in winter, during an intense frost, a circumstance which renders the action of warm currents of air, as accessory to its flight, something more than questionable. Our aeronaut may be met with in its descent over the Mer de Glace as well over the Lake of Geneva; and it will take flight as readily from a point over the frozen sea as from the heated surface soil of the valley of Chamouny.
"Several circumstances concur to shew the phenomena of ascent to be electric. The propelled threads do not interfere with each other; they are divellent, and this divergence seemed to proceed from their being imbued with similar electricity, and the character of that electricity appeared to me to be an interesting subject for subsequent research....... When a metallic conductor is brought near to the suspended spider, it disarranges its projectiles, and the insect, conscious of some counteracting agency, coils up its threads.
"When a stick of sealing-wax is brought near the thread of suspension, it is evidently repelled, consequently the electricity of the thread is of a negative character. The descent of the thread is instantly determined by bringing over it the excited sealing-wax; and if strongly excited, and the spider let fall on its surface, it bounds from it with considerable energy. On the 3d of July, 1822, at 4 P.M., thermometer 66 degrees Fahr., two aeronautic spiders, on separate threads, were brought near to each other; a mutual repulsion supervened; and when one was brought in momentary contact with the other, it immediately fell lower in the perpendicular plane.
"An excited glass tube brought near, seemed to attract the thread, and with it the aeronautic spider. When the insect was thus positively electrified, the rapidity which marked its descent, and extent of thread spun out, and which I frequently coiled up, was truly astonishing, being at least 30 feet in length."
[*J.J. Virey, Ferussac's Bulletin Sciences Naturelles, Tom. viii]
[**Memoirs Wernerian Soc., Vol. v, pt.2, 1826; and Loudon's Mag. Nat. Hist. Vol. I, 1829]
The manner in which the thread starts from the body is difficult to determine, on account of the small size of the spiders. One theory is that the spider must attach one end of its thread to a fixed object, so that the wind may have a loop to blow against. Some think it more probable that a small quantity of gummy material is emitted from the spinnerets and drawn into a thread by the current; * others, that the spinnerets of opposite sides are brought in contact and then drawn apart, forming a little web between them which offers enough surface to the wind to be blown away, carrying out the thread with it.
[*REnnie's Insect architecture, p. 381]
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