in] FOSSORES OR DIGGER-WASPS 35 



in a genus so extensively represented in number of 

 species, there is considerable variety in the choice of 

 nesting sites. Some, such as the common little 

 species C. wesmaeli, a shining black and yellow insect 

 with a minute red tip to the abdomen, and the larger 

 (7. cribrariiis, excavate tunnels in sandy soil ; some, 

 such as the equally abundant yellow and black form, 

 C. quadrimaculatus, burrow into rotten wood ; while 

 others succeed in boring into the comparatively sound 

 timber of old gate posts, wooden fences and the like ; 

 and a large number select the stems of brambles and 

 briars, boring into the pithy centres, as their place of 

 nesting. From the fact that their prey is entirely 

 composed of insects, they may without hesitation be 

 regarded as useful to mankind. I have several times 

 seen C. clavipes catching the small flies that in some 

 states of the weather accumulate in large numbers 

 upon the window panes of sunlit rooms. C. leuco- 

 stomus provisions its nest with a bright green 

 fly (Chrysomyia polita). F. Smith states that C. 

 podagricus lays up stores of a certain small species 

 of gnat. Some of the larger and more powerful 

 species, e.g. C. dimidiatus, aim at larger game and 

 succeed in capturing large blue-bottle flies; while 

 many of the smaller kinds store up midges and 

 other troublesome little insects, or collect plant-lice 

 (Aphides) from our garden plants. The full-grown 

 insects support themselves upon vegetable products, 



32 



