THE

POPULAR SCIENCE

MONTHLY.

APRIL, 1875.

THE TRIANGLE SPIDER.

BY PROF. BURT G. WILDER,

OF THE CORNELL UNIVERSITY.

TROLLING through the woods near Ithaca, New York, one October afternoon, I saw, upon a leafless hemlock-brauch, what looked like a piece of the net of some geometrical spider. Still, there was a regularity in this triangular net which did not accord with the idea of its being a fragment. A closer examination showed that its form and structure were perfect and unbroken; and moreover that, instead of hanging loosely from the twigs, it was upon the stretch, as if constantly drawn by a power at one or the other end (Fig. 1).

On touching the net to determine its degree of tension, what was my amazement to see it suddenly loosened with a snap, as if let go at one end! Nor was my wonder diminished when, a moment afterward, the the net slowly regained its original condition, by a steady pulling upon a short line connected with the apex. And now I saw the puller-a little dull-colored spider, about one-eighth of an inch long-hanging from the under side of the apex-line, and hauling it in, not "hand over hand," as at first appeared, and as one would suppose by analogy with sailors' operations, but "foot over foot; " in short, with its hinder legs moved alternately so as to gradually take in that part of the line which intervened between its body and the twig to which it was attached.

When this line was all taken in, the spider was close against the twig, and its legs were drawn together, so that the whole formed a compact brown mass about the size and shape of a raisin-seed, and differing so little in appearance from the projections of the dried hemlock-twigs among which the net was built, that I felt in part excused for not having noticed the little creature before.

So much for an introduction to a spider which was then new to me, and probably is still unknown to most of my readers. In some respects its habits are unlike those of all our other spiders; and I will here relate what I have learned during five seasons, in the hope that

others may have the fortune to clear up the points in its economy as yet undiscovered.

Our spider is thought by high authorities to be a species of the genus called Hyptiotes by Walcknaer, and afterward and more commonly Mithras; but the former name has priority. Of this genus two European species have been described; one of which, H. paradoxus, has lately been found in England, and described by the veteran arachnologist, Mr. Blackwall. Our American species seems to be that referred to by Hentz as the Cyllopodia cavata,' but his description is so brief,

FIG. 1.-NET OF THE "TRIANGLE SPIDER." about one-half the usual length. The spider, however, is shown of the natural size.

BB, the base-line attached, at C and D, to a hemlock-branch; EF G, points of attachment to the base-line of the three radii, R' to R", which converge at A, the apex of the net; I' to IIX, nine transverse or interradial double lines; S' to S", attachments of the first interradial upon the radii; A L, apex-line; 0, origin of the apex-line from a second branch; S, loop of the apex-line or "slack," between the front and hinder feet of the spider: this is better shown in the lower enlarged figure.

and in some respects erroneous (giving only six eyes, whereas there are eight), that we shall probably avoid confusion by calling this a new species (H. Americanus).

Having now identified the spider sufficiently for our present purpose, we have to inquire:

1. Which is the spider, the male or the female?

2. How is the net made?

3. How is the net used in taking prey?

4. What are the relations between this and other spiders?

1. WHICH IS THE SPIDER? As is often, although by no means

1 Boston Journal of Natural History, 1847, vol. v., p. 466, plate xxx., Fig. 3.

universally, the case among spiders, the female is the head of the family. In fact, so scarce are the males that for three years I never found one among more than a hundred specimens. This, however, is not absolute proof of their much smaller number, for they are less in size and darker in color, and, like the males of the "silk-spider of

2

FIG. 2.-At the left a female Hyptiotes, enlarged about eight diameters. The legs are marked 1, 2, 3, 4, in order from before backward. In the central figure is shown the front part of the spider (the cephalo-thorax), still more enlarged, so as to display the eight eyes arranged so as to form two crescents with their convexities opposed thus At the right is a greatlymagnified feathered bristle from the upper surface of the cephalo-thorax.

South Carolina" (Nephila plumipes), they make no nets, but seem to get a precarious living by hanging on to that of some female. Their masculine nature is seen in the structure of the "palp" or feeler, which, instead of tapering to a blunt point, as in the female, is greatly enlarged, its last segment presenting the remarkably complex structure seen in Fig. 3.'

FIG. 3.-Terminal joints of the palp or feeler of the male Hyptiotes Americanus, much enlarged. (Drawn from Nature, by Prof. W. S. Barnard.)

1 These modified palpi are undoubtedly connected with the reproductive function. Others besides myself have seen them (with other and larger species) applied to the vulva of the female during an evident copulation; but all do not assent to the generallyreceived opinion, that they are merely intromittent organs, which have first received the spermatic fluid from the testicular orifice upon the ventral surface of the abdomen. (For a note upon the subject, by Mr. Gedge, with references, see Journal of Anatomy and Physiology, 1867, vol. i., p. 371.)

It is possible that, as with the Nephila plumipes, the young males of Hyptiotes construct nets, but of this I can say nothing; for as yet I have never seen what I was certain were the eggs or the very young. Near Ithaca I have found the partly-grown spiders, during the latter part of July, and the adults are all gone before the close of November. Certain little cocoons (Fig. 4), which are quite abundant in the same localities and upon the hemlock-twigs, may prove to be made by this spider, but at present all is conjecture.

FIG. 4.-SUPPOSED COCOON (EGG-CASE) OF TRIANGLE SPIDER.

A, the cocoon, of natural size, hung by thread-lines between hemlock-twigs; B, the cocoon enlarged, seen obliquely, so as to show the triangular base.

The form of these cocoons is quite peculiar: it is that of a little sphere flattened upon one side; at three points the border of this flat side is extended into strong lines, by which the cocoon is suspended between the twigs. Its diameter is about one-tenth of an inch, but the lines are often two or three inches long. The ground-color is usually white; but there are always a few black specks, and sometimes these cover so large a portion of the surface as to make the cocoon appear gray or nearly black.

Besides these more common cocoons, the hemlock-twigs sometimes bear others of about the same size, but pear-shaped, and hanging by the smaller end upon a single short line. To identify these, the spiders should be taken in September, and kept in captivity upon hemlock-branches, so that they may make their cocoons.