COBS AND COBWEBS
A. Hyatt Verrill
Although we have all seen cobwebs and have ruthlessly destroyed them, yet few of us stop to consider how the little owners spin them. We know they are built of silk and serve as fly traps and houses for their makers, but little do we realize the amount of time, labor and ingenuity expended upon these troublesome structures. The variety in spiders' webs is almost endless, but be they the dust-catching webs of the house spiders or the dew-sparkling ones of their woodland cousins, the silk in every case is spun in the same manner.
If you look upon the lower side of a spider's body you will see a little group of protuberances, usually 6 in number. These are the "spinnerets," special organs for forming the dainty silken threads. Opening from the end of each "spinneret" are a large number (sometimes as many as 200) fine tubes. The silk, which, within the spider's body is in liquid state, issues from these tiny openings, and as it reaches the air, hardens and combines to form a single strand. When the spider wishes to spin a fine line, he places the "spinnerets" close together, while if he requires a broad band, or is in a hurry to secure some insect tangled in the web, he spreads his "spinnerets" apart, thus forming a delicate silken ribbon.
Not only can spiders regulate the size of their thread, but many species can produce elastic, sticky silk, or dry, inelastic silk, at will. These two kinds of thread are used for very different purposes, although both maybe utilized in the construction of the same web. The dry threads are always used when the spider wishes to drop from one place to another, for silken bridges from point to point, and for the stays and framework to the web, while the sticky threads are those which catch the spiders' prey, their elasticity preventing the captive's struggles from breaking them and at the same time serving to entangle him the more.
If you have ever strolled through the woods on an autumn day, you must surely have noticed the numerous round or semi-round webs spread among the bushes and trees. These are the snares of the "orb weavers" or "geometrical spiders," mostly large, fat, brightly colored or curiously shaped fellows, whose webs, when once we begin to study their structure, fill us with admiration for the builder. When one of these gaudy creatures wishes to build a web he first spins several lines extending irregularly from one twig to another where he wishes the finished web to be. These answer for a staging on which the builder can readily run back and forth while stretching the other threads. After the staging is done our busy friend fastens a thread to some twig, or to one of the lines already made, and walks along spinning as he goes, meanwhile with one of his hind feet carefully holding the new thread from becoming tangled with the object over which he is traveling. This new thread he carries around the staging until it crosses the point, where the centre of the finished web will be, then he pulls in the slack and fastening the line securely runs nimbly to the centre of the web. Here he makes fast another thread and spinning and guiding as he goes, walks back to the outer framework and secures it a short distance from the first thread. This operation is repeated until all the radiating lines are spun and in place. Now the little worker goes to the point where these spoke-like lines cross and fastening a thread, walks round and round, sticking the new thread to each spoke as he crosses it. In this way he forms a regular spiral, each turn of which is as far from the next as the spider can reach.
Now the tiny architect has the most important part of his work to perform, for so far he has merely made a frame, or support, of dry, inelastic thread. Commencing at the outer end of the completed spiral he fastens an elastic, sticky thread and travelling around his web forms another spiral. The turns of this sticky spiral are close together, and as the spider passes along he destroys the first, or dry spiral, leaving little fragments hanging to the radial lines. At last the centre of the web is reached, the beautiful geometrical web completed, and, hiding among the leaves at one side of the net or hanging head downwards from its centre, the maker patiently awaits his prey. As he hangs there he grasps several of the radiating lines with his feet in order to detect the slightest jar caused by an insect fouling the web.
One of the most wonderful of spiders' webs is that of a small, round-bodied little chap, in general appearance closely resembling some of his big geometrical cousins. These nets, which can almost always be found stretched among the branches and twigs of evergreen trees, at first sight seem simple and uninteresting affairs. They are triangular in form, composed of four radiating lines crossed by a number of coarse double threads and fastened to some convenient twig by a stout, strong thread extending from the apex of the triangle. Upon this line the owner rests, and, although at first there seems nothing strange or peculiar about his actions, if you will look carefully you may notice that the spider holds some loose thread between his legs, while his fore feet pull the rest of the web taut.
Now watch closely, and perchance you may be fortunate enough to see this little lasso-thrower catch his prey. Presently a buzzing fly, or blood thirsty mosquito, comes flying along and bumps against the web. Instantly the spider loosens the hold of his fore-feet and the web springs forward, entangling the unfortunate intruder. Then the spider draws the web tight and once more snaps it forward, repeating the operation again and again until his victim is hopelessly tangled up and the ingenious little assassin can suck its blood at leisure.
But wonderful as is this cleverly constructed trap, or lasso, more remarkable yet is the fact that many of our spiders utilize their thread for balloons, and by its aid, travel through the air for long distances, sometimes hundreds of miles. When the little aeronaut wishes to make an ascension, he climbs to the highest spot he can find, as a fence post, low bush or even the tip of a blade of grass, and holdfast by his fore-feet, stretches up his body and rapidly spins out a thread. The free end of this line is carried up and away by the breeze, until at last, sufficient silk having been spun to lift the spider's weight, he lets go his hold and gaily sails away.
Perhaps you think this simple, breeze-borne thread should not be dignified by the name of "balloon," but nevertheless the little spider can regulate his speed even better than human balloonists. If the breeze freshens he has but to gather in some of the loose silk, while if it grows calm and he shows signs of falling earthward, he can spin out yard after yard of the floating gossamer. These flying spiders are very common, and on warm autumn days we may often see hundreds of their threads streaming upward from fences, grass and bushes or blowing about in the air. Borne on the wings of a stiff September wind, these tiny adventurers travel far and swiftly and have even been seen floating safely through the air far out to sea.
Perhaps no spiders have been written and talked about as much as the Tarantulas, but although these creatures are big and ugly they are not by any means as large or formidable as their bird-eating cousins, the Mygales of Central and South America. Neither the Mygales or Tarantulas, however, are really as dangerous as many persons suppose, for although their large and sharp jaws can inflict deep and painful wounds, it is seldom that serious results follow the bites, and it is very doubtful if they ever prove fatal to human beings. I have several times been bitten by Mygales and never suffered any inconvenience, save a somewhat inflamed hand or arm.
Closely related to these big, hairy creatures are the "trap-door spiders," and although the nest of the common western species, with its neatly fitting and silken-hinged door, is wonderful enough to invariably excite interest in the beholder, yet other species show a foresight and ingenuity almost beyond belief. These fellows are not content with a single trapdoor to their houses, but for greater safety dig one or more side tunnels, also provided with doors opening into the main burrow. These underground nests serve as a resting place for their owners as well as a safe retreat into which they dart when pursued by an enemy. If their pursuer succeeds in opening the first door, the spider retreats to one of the side chambers, shuts the door behind him, and if he thinks himself still in danger, digs his way to the surface of the ground some distance away.
Although these trap-door spiders and their nests are considered as curiosities, we really have trap-door spiders in the East which make silk lined burrows in exactly the same manner as their western cousins. These spiders belong to the genus Lycosa, and look much like small tarantulas, with the exception of the jaws, which move sideways instead of up and down. The Lycosas dig their holes in open, sandy places and usually conceal the entrance by small stones, twigs, or bits of grass, and one species even builds a little watch-tower of straws above the doorway to his subterranean home.