INTRODUCTION 3 



a habit has the earmarks of great antiquity and seems to 

 indicate that the present type of nesting site is like the 

 one in which the group originated. This is confirmed by 

 the fact that the group as a whole prefers to nest in dry, 

 sunny, sandy or gravelly soil and is therefore most abun- 

 dantly represented by species and individuals in the deserts 

 of North Africa, the Southwestern United States, Central 

 Australia, etc., or in similar xerothermal localities of more 

 limited area in other parts of the world (sand-dunes, pine- 

 barrens, dry banks, roads, paths, etc.) . Probably, therefore, 

 the group originated during some period of the Mesozoic 

 when there were large tracts of elevated, arid land in the 

 interior of the continents, and this may account for our 

 failure to find any fossil remains of the primitive ancestral 

 forms. In this connection it is interesting to note that the 

 work on the habits of the solitary wasps is mostly confined 

 to particular countries in which the physical conditions are 

 such as I have described. Thus the most important contri- 

 butions to our knowledge by European observers such as 

 Dufour, Fabre, Picard, Bordage, Roubaud and Ferton, 

 have come from Southern France, Corsica and North Af- 

 rica or from the tropics, and the more important observa- 

 tions of American investigators, such as Riley, Williston, 

 the Peckhams, Hartman, Hungerford, Williams, Iseley, 

 Barth and the Raus, have been made in the Middle Western 

 and Southwestern States. 



The fact that the solitary wasps have so many and such 

 intricate relations with their inorganic and living environ- 

 ment renders their study in the laboratory impossible or, 

 at any rate, very inadequate. A few habits, such as the 

 method of constructing the nest among the mason wasps, 

 can be observed in the laboratory, and sometimes with re- 

 markable results as shown by Bordage's work on Pison 

 and Trypoxyl&n in the Island of Reunion, but a knowledge 



