2 WHEELER— THE PARASITIC ACULEATA. 



broader generalization has its attendant risks and inadequacies. If 

 I succeed in directing renewed attention to an interesting series of 

 facts and to some of the problems which they suggest, the purpose 

 of this article will have been accomplished. 



In considering the parasitic Aculeata I shall adhere to the fol- 

 lowing classification, which though in certain respects artificial and 

 unsatisfactory from the standpoint of phylogenetic development, 

 will nevertheless facilitate an understanding of the history of our 

 knowledge of the subject: 



I. Nonsocial Parasites. 



1. Solitary Bees. 



2. Solitary Wasps. 

 II. Social Parasites. 



1. Ants. 



a. Guest Ants. 



b. Slave-makers. 



c. Temporary Social Parasites. 



d. Permanent Social Parasites. 



2. Social Bees. 

 3- Social Wasps. 



The solitary bees may justly claim our attention first, because 

 they comprise such a large number of parasitic forms which have 

 been objects of study for more than a century. The taxonomy of 

 the bees, however, notwithstanding the number of able investiga- 

 tors they have attracted, is still in a very unsatisfactory state. The 

 very numerous species are often distinguishable only by very minute 

 or dubious characters, so that many of the genera are large, homo- 

 geneous and widely distributed. Even the generic characters are 

 often very feeble as compared with those employed by taxonomists 

 in other Aculeate families. Hence also the higher groups, such as 

 the tribes and subfamilies are so poorly characterized that no two 

 melittologists agree on their limits or number. The wing venation 

 is extraordinarily uniform throughout the whole family and the 

 taxonomic use of the mouthparts encounters the usual difficulties 

 which beset the employment of delicately adaptive structures. All 

 the members of the group are of comparatively recent phylo- 

 genetic development and very highly specialized in adaptation to the 



