372 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



V. 



Examples of cocoon mimicry are furnished by certain American Orb- 

 weavers, as, for example, Cyclosa caudata and Cyclosa bifurca. These 

 spiders make cocoons which in general shape and color closely 



Cocoon resemble the mother. The cocoons are hung in a connected se- 

 JVLiiTiicrv. 



ries within the orb, a rather exceptional disposition. The mother 



clings to the lower cocoon of the string, and might easily be confounded 

 with her cocoon. The conical shape of Caudata's cocoon is paralleled by the 

 compressed apex of her abdomen, which has given her the name of the 

 Tailed spider. Her color also, a grayish white mottled with blackish mark- 

 ings, increases the resemblance between her and her egg sac, which is com- 

 posed of whitish silk covered over with the scalpage or debris of slaugh- 

 tered insects. Cyclosa bifurca is colored green, and her cocoon has a 

 greenish hue. (See Plate IV., Figs. 10, 11, 12.) 



The suggestion has been made that placing cocoons of this particular 

 form within the limits of the spider's snare, has a tendency to deceive 

 attacking insects, such as raiding mud dauber wasps or arachnophagous 

 birds. Professor Peckham alludes to the fact that Caudata, when a vibra- 

 ting tuning fork is placed near her, instead of remaining steadfast upon 

 her snare, drops from it in the way common to Orbweavers, and thus be- 

 trays her position and exposes her person. 1 The implication is that, were 

 the resemblance really protective, the spider would have held steadfast 

 and not acted as she did. 



On the contrary, it seems to me that this fact does not really break 

 down the force of the suggestion that such mimicry may be protective. For 

 we must conceive that a raiding bird or wasp, if deceived at all 

 caudat ^J the appearance of the cocoons hanging in the snare, would 

 flutter from one cocoon to another until at last the spider would 

 be reached at the end of the string. The vibration of the wings of a bird 

 or insect would be the spider's warning of the nearness of -an enemy, 

 and her chance of safety would certainly be to drop from her web at 

 once. Of course, if the assailant should first strike the spider herself her 

 opportunity to escape would not be great ; but supposing that there is about 

 an equal chance that the assailant would strike one of the cocoons, think- 

 ing it to be a spider, in that case the mother has a fair opportunity to 

 escape, and her chances are in proportion to the number of cocoons in the 

 string. Mr. Peckham's experiment, therefore, instead of showing against 

 the suggestion that the cocoon mimicry is useful to Caudata, seems to me 

 to be entirely in harmony with it. 



In this connection it is to be noted that the young of Caudata are in 

 the habit of hanging upon their orbs little puffs of silk closely resembling 



1 " Mental Powers of Spiders," page 395. 



