268 ME. K. I POCOCK — MIMICRY IN SPIDERS. 



that the special advantage the mimetic species derive from being avoided by 

 Porapilidse and Ichneumonidas has hitherto been pointed out *. 



Two conclusions appear to me to emerge very clearly from a study of the 

 genuine cases of mimicry in Spiders. 



1. There is no reason to suppose that any of the mimetic species are them- 

 selves specially protected in any way or inedible. Therefore their imitation 

 of other animals that are avoided by the enemies of spiders is mimicry in the 

 Batesian and not in the Miillerian sense of the word. In other words it is 

 true mimicry. 



2. Since it can be shown that the mimicry has in every case a survival 

 value, the modifications that have brought it about fall within the scope of 

 Natural Selection. 



Doubtful cases of Alimicri/ in Spiders. 



The instances of mimicry already cited in this paper cannot in my opinion 

 be questioned. The same assurance cannot, however, be held about the 

 following cases. 



A possible case of protective mimicry in nest-building is furnished by the 

 burrow of Doliclioscaptus inops, a species of the Cyrtaucheniinse that lives in 

 Algeria. Round the aperture of the burrow is erected a low chimney rising 

 to half an inch or more in height, and consisting of silk stiffened with debris 

 of various kinds which conceals the silk and makes the burrow resemble those 

 formed by the solitary bees Odynerus or AntlwpJwra f. 



The advantage the spider derives from this resemblance, it may be suggested, 

 lies in the immunity these bees enjoy to the attacks of mason-wasps, for the 

 latter, mistaking the spider-burrows for those of the bees, would pass them 

 by without further enquiry. But until it is definitely established that the 

 nests of the bees occur in the same locality, the evidence for the view above 

 stated remains unsatisfactory. 



* Although not strictly speaking belonging to the subject-matter of the present paper, 

 the following observation is, I think, worth putting on record. 



"While watching one of the solitary digger-wasps at work last summer hunting for spiders 

 with which to provide her larvae, I saw her dislodge from a cranny between two stones an 

 immature specimen of a species of Plialangium, possibly P. cornutiim. She ran swiftly in 

 chase of the Arachnid, but the moment she touched it with her antennae turned aside and 

 let it go. Although it is well known that the Phalangidse possess stink-glands opening one 

 on each side of the cephalothorax, which have been held to be of protective significance, I 

 am not aware of any recorded evidence of their being rejected by the enemies of spiders. 

 Certainly no instance of this has previously come under my own notice. It is possible of 

 course that the wasp may have rejected the Plialangium for other reasons ; but I think the 

 escape of the Arachnid may be regarded as probably due to its inedibility owing to the 

 smelling secretion it exudes. 



t Simon, Actes Soc. Linn. Bordeaux, xlii. p. 394, pi. 12. fig. 6, 1887. 



