21S ANIMAL COLORATION. 



is perfectly true tliat no animal, however perfect its protection, 

 can wholly escape ; and it is, as has been pointed out in another 

 case, no argument against mimicry to be able to show that one 

 group of birds has acquired the habit of feeding exclusively upon 

 ants. But when we learn that such different birds as domestic 

 fowls, sparrows, partridges, woodpeckers, etc., also eat them, 

 it seems rather doubtful whether the advantages gained by 

 the protection afforded would be sufficient to account for the 

 mimicry of the spiders on the theory of natural selection. 



Dr. McCook also points out that the greatest destruction of 

 spiders takes place when they are very young — when, therefore, 

 the protective mimicry would be perhaps hardly established, 

 or, if sufficiently evident to a naturalist, not sufficiently so to 

 their enemies to serve any useful purpose. When excessively 

 minute the young spiders have many enemies besides birds, 

 which would take no account whatever of a slight resemblance 

 to an ant; again, all the young Saltigrade spiders (the ones 

 which show the mimicry) float in the air by their parachutes, 

 and countless thousands must fall a prey to swallows. Excep- 

 tion may, perhaps, be taken to the objection that no spider 

 mimics a wasp. 



But on the theory that variation is indefinite and on all sides, 

 it would seem on a priori grounds probable that spiders would 

 be met with which do mimic wasps, the most deadly enemies 

 with which the spider tribe is confronted. Perhaps Dr. 

 McCook's suggestion that the mimicry of ants by spiders 

 renders this unnecessary, because the spiders are thereby 

 protected against wasps, does away with any force that this 

 objection may have. Wasps do not appear to prey upon ants. 

 Dr. McCook, however, goes a little too far in implying that 

 various members of the same group, Hymenoptera, do not prey 

 upon each other ; they certainly do in some cases, for hornets 



