Hentz observed the species on limestone rocks on the banks of Cyprus Creek, and in moist places in North Alabama. Its congener, U. mammeatus, he found dwelling most frequently in cavities, among large logs, and in hollow trunks of trees.1 Emerton found Plumipes between loose stones or low bushes in New England. Mrs. Peckham almost invariably found this species building in dead branches, six out of seven being thus located.2 She gives an apt abstract of its habits. In form and color it resembles a scrap of bark; its body is truncated and diversified with small humps, while its first legs are very uneven, bearing heavy fringes of hair on the tibia, and having the terminal joints slender. Its color is a soft wood brown or gray, mottled with white. It has the habit of hanging motionless in the web for hours at a time, swaying in the wind like an inanimate object. The strands of its web are rough and inelastic, so that they are frequently broken, and this gives it the appearance of one of those dilapidated and deserted webs in which bits of windblown rubbish are frequently entangled.
Baron Walckenaer says that the closely related European species, Uloborus Walckenaerius Dugès, generally spins its horizontal snare between the stems of rushes in dry and warm places, which resembles that of Epeira in form, but of looser tissue.3 Hahn found the species in the neighborhood of Nuremberg on the edge of forests, building its snare between young pines. Simon says that the species lives upon dry brambles or in the cavities of old walls, that it is always found stretched lengthwise beneath its snare, and is readily confounded with adjoining objects.4 Uloborus Walckenaerius is one of the spiders inhabiting Palestine, being among those listed from Syria by Mr. Cambridge.5
I have never seen the orbs in any other than a horizontal position. They measure from three to four and five and a half inches in diameter. The hub is generally closely and beautifully meshed, like the snare of the Labyrinth spider, and the central space is entirely filled up by concentrics, corresponding with those composing the notched zone in the ordinary webs of Orbweavers. The radii diverge in the ordinary way, but seem to be of a rather delicate material. In the Juniata colony above named many of the webs were surrounded by what appeared to be the collapsed remains of a former snare. The spiders appeared to have cleared away and pushed back the old broken webs so as to make space for new ones, and the fragments occupied the margin of the orb space close up to the points at which the foundation lines were attached to the adjacent foliage. (See Fig. 161.) On one of these webs I counted thirty-six radii and twelve spirals, not including among the latter the concentrics which fill up the central space. The hub measured a quarter inch in diameter, and the distance between the concentrics was one thirty-second of an inch. Beneath the orb there extended a mass of retitelarian lines, somewhat after the manner of the Orchard spider, but not so abundant. The central spirals gradually opened as they approached the true spiral space, and were separated by distances ranging from one-eighth to one-fourth inch. A notched ribbon about an inch long was spun on each side of the hub, gradually terminating in a point. The central spirals crossed the ribbon at the points of its angular scallops. The hub was one-fourth inch wide.
Snares of Uloborus found upon the banks of Bride’s Run, at the outlet of Bride’s Pond, near Niantic, Connecticut, were spun in the cavities of old stumps, or upon the ferns and grasses near the banks of the stream. The hub was checkered or meshed somewhat like the notched zone of Epeiroids. The notched or central spirals seized the points of the little ribbon that extended centrally through the horizontal orb. The spirals of one orb were twenty-two in number, the radii thirty-nine and forty. The spirals continued close up to the margin of the notched zone, without any interspace, and the web was about four and a half inches in diameter. (See Fig. 160.)
A striking peculiarity of the orbs of this species is the ribbon decorations which are quite characteristic, and unite the spinningwork of the genus with that of such genera as Argiope and Acrosoma. Perhaps the most frequent form of decoration is a scalloped band about one thirty-second inch in width, which crosses the central part of the, orb, being scarcely perceptible at the hub, and gradually diminishing towards the circumference of the orb. Where the spirals cross, this ribboned spinningwork is pulled into points, thus giving the band the toothed or scalloped appearance represented at Fig. 162. The distance between the spirals was from one-fourth to one-eighth of an inch; the distance across the band from point to point about one thirty-second of an inch.
Another form of decoration shows simply the addition on one side of the hub of a second ribbon, which makes an angle with the first. In this snare the spider hung beneath the hub, with its fore and hind legs respectively attached to the points where the ribbon joins the hub.
The most remarkable decorations of this sort I found upon the orbs of Uloborus mammeatus in Texas. They formed interesting and beautiful examples of this character of spinningwork, which is more easily illustrated than described. Fig. 163 represents one web. The upper ribbons, traversing nearly the entire area of the hub, were very much the same as the last described, except that on one side the spinningwork was greatly thickened at the termination, giving a club shaped appearance. On each of the other sides of the hub were thrown two parallel semicircular bands slightly separated from each other. In another snare, represented very imperfectly, indeed, at Fig. 164, the longitudinal bands were lacking, but instead of them a series of four or five circular bands encompassed the hub. My sketches, taken upon the spot, do not show that these bands were concentrics, though I have been inclined to think that such might have been the case. At one side of this orb was stretched a ladder like structure leading from the hub to the outer foundation lines. This was a very peculiar formation., and reminded me somewhat of the zigzag band characteristic of Argiope cophinaria, but the rounds were not continuous as with that spider.
The purpose of these ribbons I have never been able to determine satisfactorily. I have called them decorative, not because I imagine that the purpose of the spider in placing them upon her web is in anywise analogous to the human sentiment expressed by that word, but simply as a convenient term to indicate the character of the spinningwork as it presented itself to my own mind. Certainly it did greatly enhance the beauty of the delicate structure. It is probable that these decorative ribbons or bands serve to protect the spider herself, and may also be of service in strengthening the web. But I have sufficiently expressed my opinion on this subject when treating of the snare of Argiope. (Chapter VI.)
No one who has studied with any care the spinningwork of the Orbitelariæ can doubt that the web of Uloborus is that of a genuine Orbweaver. In its round shape; in the arrangement of lines radiating from the centre; in the structure of the hub; in the preliminary spiral scaffold; in the central concentrics, which correspond with the notched zone; in the form and distribution of the spirals; in the character of the ribbon decorations; in the manner in which the snare is swung to foundation lines in whatever site it may be placed; in the position of the spider underneath the web;in all these points the spinningwork of Uloborus is analogous to that of Orbweavers, especially Tetragnatha, or of the Orchard and Hunchback spiders.
There is, however, one important difference. The spiral concentrics, instead of being composed of single lines covered with viscid beads, as in typical snares of the Orbitelariæ, are composed for the most part of several very delicate filaments, although in certain parts the thread is single. To threads and filaments alike are often attached a number of minute objects, opaque, and for the most part amorphous; but many of them being very small globes of a yellow color, perhaps the pollen of flowers. They adhere to the single threads, but more fully to the portions containing several distinct filaments. These opaque objects have so much the appearance of beads that a careless observer is likely to be deceived by them; at least, I was thus led astray in my first studies of the Uloborus snare. There are, however, no viscid beads upon any of the lines, although the thread is certainly very adhesive, chiefly I suppose by reason of the delicacy and flocculence of the fibre. The smooth point of a pencil touched to it does not adhere; but when my finger was laid upon a spiral it adhered as in the case of a beaded web.
In this respect the snare of Uloborus resembles that of the Triangle spider, Hyptiotes cavatus, and also certain species of the Clubionidæ, such as Dictyna philoteichus and other species of that genus. This flocculent web was discovered and described by Blackwall, and is produced by special organs known as the cribellum and calamistrum. The calamistrum is located upon the metatarsus of the hind pairs of legs. It resembles somewhat in form the flyers upon an old fashioned spinning wheel, and is apparently used to separate into a flossy mass the threads of silk as they issue from the spinning glands. Bertkau, in all article on the cribellum and calamistrum, has shown certain secreting glands at the ends of the fine tubes which have their outlets in the former organ. It is not improbable, in view of this discovery, that the viscidity of the flocculent spirals of Uloborus and other spiders possessing this organ is caused in some measure by a slight secretion from these glands.
It is the possession of cribellum and calamistrum by Uloborus and Hyptiotes which has led various arachnologists to separate these two genera from the Orbweavers. Emerton, for example, following Blackwall, Keyserling, and Bertkau, assigns them to the Clubionidae. Without entering at length into the reasons, based upon structure, for dissenting from this opinion, I have felt constrained, on the grounds of their spinningwork alone, to place both these genera among the Orbitelariæ, where indeed such a distinguished systematic arachnologist as Professor Thorell has already placed them, and continues to keep them, notwithstanding all the objections that have been advanced by the able naturalists who have espoused the other view.
Mr. Emerton has made some studies of the web of Uloborus Walckenaerius, the common species of Northern Europe. I reproduce his figure (Fig. 167), which represents an unfinished web of this species seen in France. It shows the central part still occupied by the preliminary spirals or scaffolding, while the outer part is covered with curled threads, and the smooth spirals cut away (or not yet inserted), leaving thickened spots or ribbons on the rays. In the finished web most of the spirals pass regularly around, but the outer ones are often more or less irregular, as in Epeira webs, according to the shape of the space in which the web is made.
According to this author, Uloborus, after inclosing her eggs in the cocoon, becomes careless about her web, and repairs it only enough to keep the cocoons in place, so that many imperfect and irregular webs are found at the cocooning season. The only web of Uloborus plumipes seen by Emerton was imperfect front the above cause, but was evidently the remains of a nearly round web, the rays meeting somewhat nearer the upper than the lower edge.
The same author says that the spiral lines of Hyptiotes and Uloborus have a strong, smooth thread through the centre. That of Hyptiotes, which he examined fresh, had the finer part arranged in regular leaves or scallops, in which the separate fibres could not be distinguished. The thread of Uloborus, at least when old and dried, had the loops longer and less regular, and he had not been able to distinguish the separate fibres except at the edges of the band. To my eye the spiral seemed to be a single continuous flocculent filament without any supporting thread, thus differing from Hyptiotes. But of this I am not confident. Under a common hand lens it has a milky or filmy hue.
The position of the spider upon her snare is very much like that of Tetragnatha. I have found her stretched out underneath the hub, with the legs extended fore and aft almost in a straight line with the ribboned decorations to which the feet clung. Sometimes, however, she turned and hung beneath the hub at a position at right angles with the ribbon.
One young specimen, captured upon her snare, I saw repairing the broken margins of her web. It was done line after line, one radius and one spiral at a time, precisely in the manner common to other Orbweavers. The broken lines were cut out, and new ones substituted, or were picked up by the spider’s feet, spliced, and stretched into position. She worked very deftly and rapidly. I saw her capturing a small insect, a gnat. The two hind legs were used for rapidly pulling out the enswathing thread, while the second and third legs revolved the insect and held it to the web. According to Hentz, Uloborus has the habit of violently shaking her web when threatened.
But when at rest he always found it in an inverted position underneath its orb, with its hind legs extended in parallel lines like Tetragnatha. This record of habits, imperfect as it is, indubitably places Uloborus among the weavers of orbwebs.