MIMICRY IN SPIDERS. 365 



the emmet in order to accomplish the destruction of vast numbers of them, 

 as I can fully testify. As the Orbweavers and Lineweavers do not leave 

 their snares to capture prey and move among the ants after the fasliion 

 of the prowling Saltigrades that do mimic ant forms, the fact of ant re- 

 semblance, should it exist among them, must have a quite different solu- 

 tion. One could suggest, in their case, a protective value in resemblance 

 to wasps, but none at all as against ants. 



III. 



Another style of mimicry among spiders is resemblance to forms of 

 objects among which they live, as with Tetragnatha extensa. This aranead 

 has a long and narrow body, of a cylindrical shape, not unlike 

 Local, or g^ small twig in appearance. Its colors are delicate green, yellow, 

 „^™^ 7 and gray, thus increasing its resemblance to the plant. But the 

 ronment. >^ost striking feature of the mimicry is the habit of drawing to- 

 gether the four hind legs until the joints closely approximate 

 each other, stretching them straight backward, and treating the two pairs 

 of fore legs in the same way, stretching them out forward. (Plate III., 

 Fig. 6.) Thus the spider is extended along the stem of the plant in a 

 straight line, so that her body closely resembles the object upon which she 

 lies. The habit prevails in all known species of the genus. In this case, 

 although we concede that Tetragnatha has had no control over her own 

 particular form and ^its resemblance to a small twig, we must allow that 

 her action is a matter of personal volition, and appears to be exercised 

 with deliberate purpose to conceal her presence. Yet, the behavior of the 

 spider frequently compels one to wonder how the supposition of mimicry 

 can be harmonized therewith. 



For example, the Peckhams record that a male Tetragnatha grallator, ' 

 when touched as he hung in the web, ran to a branch, whereon he stretched 

 himself. In this position he was almost indistinguishable, as his 

 ^' color was exactly like that of the branch to which he clung. 

 The branch was gently shaken, but instead of keeping quiet he 

 ran a little way and then stretched ovit again. This he repeated, stupidly 

 betraying himself as often as the branch was touched.'^ One would think 

 that Nature, having taken pains to produce such a striking protective 

 mimicry, would not liave failed to make it useful by imparting a corre- 

 sponding instinct that would adapt behavior to opportunities. 



A Laterigrade spider, Tibellus, which has at least one quite common 

 representative in the United States, has a habit not very different from 

 Tetragnatha. Tibellus oblongus is' abundant in many marshy places in 

 the south of England. It has an elongated oval body, with longish legs, 

 and is of a uniform dull yellowish hue ; it is an exceedingly active spider. 



T. olotifjatji Walck. * Mental Powers, page 411. 



