186 ENTOMOLOGY. 



American wasp (Mischocyttarus), which is suspended by a 

 long pedicel, the cells, few as they are, are arranged in two 

 stories. The transition from this form to the nests of 

 Vespa and allied forms, which are covered in with walls of 

 paper with a single entrance, is not great. The paper- 

 wasps begin to build in early summer, and we could then 

 begin to form a series of nests in different stages of con- 

 struction which would be very instructive. 



From among the bees there can be selected a series, 

 showing that at the outset bees began, so to speak, in an 

 uncertain and tentative way to build their homes. With- 

 out much doubt the solitary bees preceded in geological 

 history the social species, though at present the geological 

 record is a blank, for species of Andrena, Xylocopa, 

 Bombus, and Apis occur in amber and other Miocene 

 deposits, and we know as yet nothing of the geological 

 succession of bees, none being found in the Eocene 

 Tertiary. 



As with the wasps, we may begin our review of the evi- 

 dences of the nesting skill of bees by first considering those 

 that simply tunnel the soil, as Andrena, which makes its 

 nests in pastures, consisting of a straight tubular well or 

 shaft, from which diverge short passages leading into the 

 brood-chambers (Fig. 226). 



Certain other bees excavate tunnels or refit the hollows 

 of elder and other pithy shrubs. The species of Osmia, 

 little green and blue bees, build oval cells of mud, placing 

 them in different situations, either under stones or in part- 

 ly decaying trees. Osmia siinillima, one of our commonest 

 species, is shrewd enough to avail itself of the empty galls 

 of a Cynips common on the oak, placing them in a row on 

 the vaulted arch of this large oak-apple. 



A step higher brings us to the leaf-cutter bees (Me- 

 gachile), which cut out circular pieces of rose-leaves, a 

 single bee sometimes building thirty cells, using during the 

 process as many as a thousand pieces. With the pieces 

 thus obtained she lines tubular hollows in trees, etc., and 



