n] FOSSORES OR DIGGER-WASPS 13 



when in motion, against the pale brown sand. The 

 other (Philodromus fallax\ though quite as abund- 

 ant, is extremely hard to detect for its colour exactly 

 matches the surface of the sand ; and even when the 

 spider is moving, the eye often fails to locate it though 

 the observer is vaguely conscious that something 

 within the field of vision has moved. It is thus 

 difficult to avoid the conclusion that the wasp uses 

 her eyes in addition to her olfactory organs in her 

 quest, and that the colouration of Ph. fallax is not 

 without its value. Every individual P. plwnbem 

 does not behave in precisely the same fashion ; there 

 are degrees of intelligence among them. I have 

 observed some which, like the above, took no pains 

 to conceal their victim when they left it during their 

 hasty visits to headquarters ; while others that I 

 have watched invariably buried their spider in the 

 sand before quitting it. In one instance this tem- 

 porary burial was always carried out near some 

 conspicuous object, such as a small tuft of grass, a 

 dead reed, or other similar landmark. The associa- 

 tion in the wasp's mind between the site of her 

 cache and the nature of the landmark was very 

 evident; for if a tuft were the landmark then 

 other tufts were often inspected during the search 

 for the right one; also when I moved a dead reed 

 near which the spider had been buried the wasp was 

 much bewildered and divided in mind between the 



