14 THE SCOTTISH NATURALIST 



they are smoothwalled and lined with a varnish that probably 

 keeps them dry. The burrow itself is not so varnished. 

 The full number of brood cells according to my observations 

 is six. Each burrow with its brood chambers is a self- 

 contained dwelling, there being no common tunnel of 

 communication between the nests of the various bees as 

 is the case with HalicUis. Before ovipositing, Andrena 

 provisions the brood cell with a store of food for the future 

 larva, in the form of a paste of honey and pollen worked into 

 a pill-like ball ; upon this she lays her &%^. The rate of 

 manufacture of the pollen balls and doubtless also the length 

 of the period of incubation of the Qg^, depend on weather 

 conditions to which the Andrena bees are very sensitive. In 

 dull cold weather they remain within their burrows in an 

 inactive state — males as well as females. When the 

 burrowing instinct is upon her, a bee will work very rapidly. 

 One captured in the act of commencing to excavate, was put 

 into a tumbler, three quarters filled with sand well pressed 

 down. As the bee became much excited on finding herself 

 imprisoned, the covered tumbler was placed in a dark 

 cupboard, and when, an hour later it was examined, the bee 

 had entirely disappeared within a burrow she had made. 



In excavating many burrows in a sandy bank in 

 Argyllshire during the first half of July I found the contents 

 of the brood chambers varied considerably. Some contained 

 a tiny globular crumb of pollen paste, the nucleus of a pollen 

 ball ; others a full-sized ball. Others held a ball being 

 devoured by a newly hatched, or a large bee grub ; and in 

 a few it was found that a dipterous maggot was eating the 

 pollen ball. On sunny July days this crowded sandbank 

 presents an interesting spectacle. Numbers of bees may be 

 seen returning to their nests, the masses of yellow pollen 

 with which they are laden rendering them conspicuous 

 objects as they fly. But the sandbank is also the haunt of 

 a grey fly, an apparently lethargic creature that spends the 

 bulk of its time sitting motionless on stones or heather-stems 

 among the bee-burrows. As the pollen-bearing bees arrive, 

 and hover over the bank, each looking for her own entrance 

 hole, the flies rise into the air to meet them, and each fly 



