Our understanding of the phylogeny of cleptoparasitic bees has long been a problem. Major contributing reasons for this problem is that parasitic bees have undergone 1) parallel reductions in their pollen transport systems and 2) parallel modifications of other adult morphological features. Thus, their relationships to nonparasitic relatives may be obscure and their relationships with one another are difficult to asses in some cases. Recent studies of the biologies of cleptoparasites and of their immature stages reveal that parallelisms and convergences in behavior and in the anatomy of immatures also exist among the cleptoparasitic lineages. Examples will be presented to illustrate this. However, other examples will demonstrate that data from these studies are useful in analyzing phylogenetic relationships.