ANIMAL BEHAVIOR, WITH EXAMPLES 173 



upon his spider associate and captures and kills the spider with 

 as much unconcern as he would a fly. 



In early August, the whitish crab-spiders of various sizes 

 and ages take certain prey according to their dimensions. One 

 day I found one in the centre of the cup-shaped depression of 

 a wild carrot flower, with his dark, caliper-shaped legs spread 

 wide apart. It was here seen how quickly he could distin- 

 guish between an enemy and his prey. A small black wasp 

 alighted on his adopted claim, and instantly the spider slipped 

 out of sight under a little bower of overhanging petals. It 

 was well that he did sUp out of sight, for this wasp often cap- 

 tures spiders to store in her underground nest. He kept quiet, 

 but watchful, and as soon as the wasp retired he came back 

 again to his exposed quarters. When the larger flies and bees 

 appeared, this veritable insect "trap" moved a little nervously, 

 but did not attack them. It is obvious that he is obliged to 

 be careful in the selection of his victims, for if the mistake 

 were made of attacking too large a fly or bee the shy spider 

 might be either stung or carried off his estate. With patient 

 discretion he waited until a desired fly appeared, when from 

 the lace folds he sprang forth, closing his front legs on his 

 victim like a flash. Were the ambush bug the only enemy 

 of the insect visitors the mortality in insectdom would be 

 considerably circumscribed. But when this assassin's work is 

 added to that of its distrustful neighbor, the almost invisible 

 crab-spider, I know not the great number of deaths assignable 

 to the combined attacks of these disguised foes. 



