WASPS, SOCIAL AND SOLITARY 



cells, not by solid partitions, but by numerous granules 

 of earth, which are used by the larvae for forming the 

 case of the cocoon. One raspberry stalk that we opened 

 had at the bottom six of these mud cocoons, and above 

 these three larvae eating, each in its own compartment, 

 the provision in this case consisting of immature bugs 

 of the genus Pamera. Sometimes the stalk which is 

 being filled by Plenoculus attracts the fancy of a bee or 

 of another wasp, as is shown by the upper cells being 

 filled by Osmia or Crabro, or sometimes Plenoculus 

 builds above the bee cells. When a number of wasp 

 eggs are placed in a plant stem, the last one laid is the 

 first to hatch. The different habits of the Hymenoptera 

 in this respect are very interesting. In the case of Cera- 

 tina dupla, the small carpenter bee, the egg first laid 

 hatches first, those above following in regular order. 

 The lower ones wait patiently in their cells until the one 

 in the top cell has matured, and then they all come out 

 at once. When two species occupy the same stalk, the 

 lack of adjustment probably results in the destruction 

 of those lower down, excepting in the case of the cuckoo 

 flies, which have acquired the habit of gnawing their 

 way out at the side of the stem. 



