CARPENTERS AND WOOD-WORKERS 105 



tough brownish cocoons. The perfect insects are 

 black and yellow (some all black), often banded in 

 a very wasp-like fashion, and they have broad, 

 square-cut heads. The usual food stored for their 

 grubs consists of two- winged flies (Diptera), and in 

 some cases each species of Crabro has a particular 

 species of fly it uses for this purpose ; but there 

 are several remarkable departures from the rule. 

 Three of our native species (Crabro tibialis, C. 

 clavi-pes, and C. cafitosus) use bramble-stems for 

 their burrowing operations. C. signatus and C, 

 dimidiatus bore into posts and stumps, the latter 

 species storing up blue- bottle flies. C. leucostomus 

 has a preference for the soft wood of decaying 

 willow-trees, and as grub-food selects the bright- 

 green fly Chrysomyia polita. C. quadrimaculatus, 

 C. chrysostomus, and C. interruptus also burrow into 

 dead wood. 



The Peckhams found C. sexmaculatus burrowing 

 into the sound wood of an above-ground root of 

 the lime-tree. Five of them were sinking their 

 shafts side by side — 



"... sawing and cutting in the most humdrum 

 and practical manner. One of them, presumably the 

 earliest riser, was well down in the root, and came 

 backing up once in a while, pushing a lot of wood- 

 dust out of the hole. This was spread out by 

 means of legs and mandibles, and was then blown 

 away by the fanning wings of the little worker, 

 who circled about just above the ground until the 

 last grain had disappeared. . . , After this series of 



