[10] Abbreviated from the occasional Papers of the Natural History Society of Wisconsin, Vol. I., 1889. By permission.
There are, among spiders, two forms of protective modification: the first, including all cases of protective resemblance to vegetable and inorganic things—that is, all modifications of color or of color and form that tend to make them inconspicuous in their natural relations—I shall call direct protection. The second form, which I shall call indirect protection, includes two classes, the spiders which are specially protected themselves and those which mimic other creatures which are specially protected.
Spiders are specially protected when they become inedible through the acquisition of hard plates and sharp spines. The modification of form is frequently accompanied by conspicuous colors, which warn their enemies that they belong to an unpalatable class.
The second class of indirectly protected spiders—those that mimic specially protected creatures—presents some difficulties, since it is not always easy to determine whether the purpose of mimicry is protection or the capture of prey. The resemblance may, as is frequently the case in direct protection, serve both purposes.
In looking for instances of protective form and color among spiders we encounter one difficulty at the outset. The meaning of a protective peculiarity can be determined only when the animal is seen in its natural home. The number of strangely modified forms depicted in descriptive works on spiders is enormous. Bodies are twisted, elongated, inflated, flattened, truncated, covered with tubercles or spines, enclosed within chitinous plates, colored like bark, like lichens, like flowers of every imaginable hue, like bird droppings, like sand or stones, and in every one of these modifications there is doubtless an adaptation of the spider to its surroundings which, when it is studied out of its natural relations, we can only guess at.
It has been well said that in these protective resemblances those features of the portrait are most attended to by nature which produce the most effective deception when seen in nature; the faithfulness of the resemblance being much less striking when seen in the cabinet....
Direct Protection. Resemblances to Vegetable and Inorganic Things.—As a general rule the forms and colors of spiders are adapted to render them inconspicuous in their natural homes. Bright colored spiders, ... either keep hidden away or are found upon flowers whose tints harmonize with their own. This rule, while it has numerous exceptions, is borne out by the great majority of cases. A good illustration is found in the genus Uloborus, of which the members bear a deceptive resemblance to small pieces of bark, or to such bits of rubbish as commonly become entangled in old deserted webs. The only species in our neighborhood is Uloborus plumipes, which I have almost invariably found building in dead branches, where its disguise is more effective than it would be among fresh leaves. The spider is always found in the middle of the web, with its legs extended in a line with the body. There has been, in this species, a development along several lines, resulting in a disguise of considerable complexity. Its form and color make it like a scrap of bark, its body being 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; this gives it the appearance of one of those dilapidated and deserted webs in which bits of wind-blown rubbish are frequently entangled....
Out of seven examples of the species taken during one summer, five were found in dead tamarack branches, one on a dead bush, and the seventh, an interesting variety, under the eaves of a porch. My eye was caught by what seemed to be a string of eleven cocoons (it is not common to see more than four in a web). On attempting to take them down I was surprised to see one of the supposed cocoons begin to shake the web violently. Ten were what they seemed to be, but the eleventh was the mother spider, whose color and general appearance was exactly like that of the little cases that she had made for her eggs....
We come now to a large and interesting class in genus Epeira. I refer to those species, mostly nocturnal, which are protected during the day, not by hiding in crevices, nor in any way actually getting out of sight, but by the close resemblance which they bear to the bark of the trees to which they cling. This resemblance is brought about in two ways; through their color, which is like that of wood or lichens, and through their tuberculated and rugose forms, which resemble rough bark.