Drapetisca socialis, while quite a different looking spider, is protected in the same way—­by its resemblance to the bark upon which it lives.  Emerton speaks of finding it on the bark of spruce trees, which it “closely resembles in color.”  Menge says that it is common in Prussia, where it is seen in great numbers on fir trees, whose spotted bark it resembles in color, so that it is not easily seen.  We have found them, most commonly, upon birch trees, and in this situation their color adaptation is perfect.  Both the spider and the peeling bark of the tree are of a light silvery brown, covered with little blackish marks.  On the bark these marks are, of course, irregular, while on the spider they form a pattern made up of straight and curved lines and dots, the legs being silvery, barred with blackish.

Another little Theridion that is found on birch bark has the same colors arranged a little differently.  The abdomen above has a large and peculiarly irregular black patch, which shades off into mottled brown and black on the sides and below.  The cephalothorax has stripes of brown and black, and the legs are barred with light and dark brown.

Spiders that live upon walls, fences, tree trunks, or on the ground harmonize in color with the surfaces upon which they are found, being usually gray, brown or yellow, mottled with black and white.  This proposition is so well established as to need but few illustrations.  The Therididae furnish many examples, as T. murarium, a gray spider varied with black and white, said by Emerton to live usually “under stones and fences, where it is well concealed by its color”; and Lophocarenum rostratum, a yellowish-brown spider, found among leaves on the ground.  Among the Attidae bright sexual coloring often gains the ascendancy over the protective tints, yet this family gives us good examples in such species as M. familiaris and S. pulex.

To these may be added an as yet undescribed species which we discovered last season in a neighborhood that we had searched thoroughly for eight summers.  We found the new spider in great numbers, but could only detect it by a close scrutiny of the rail fences on which it lived, its color being dark gray....

[Illustration:  FIG. 5.  ORNITHOSCATOIDES DECIPIENS (from Cambridge).]

The last instance that I shall cite is a predaceous spider which is disguised from both its enemies and its prey by an elaborate combination of form, color, position, and character of web.  I refer to Ornithoscatoides decipiens (Fig. 5), first described by Forbes and afterwards by Cambridge, the latter author giving in the same paper descriptions of three other species of the same genus, whose habits have not been noted, but whose protection is evidently of the same order as that of decipiens.  I give Forbes’s interesting account of his capture of decipiens, quoting also the remarks by which Cambridge prefaces his description, since his explanation of the gradual development, through Natural Selection, of the spider’s deceptive appearance applies as well to all the cases of protective disguise which have been here enumerated.