WHEELER— THE PARASITIC ACULEATA. 9 



" When quickly unearthing a nest which I had seen Sphccodcs entering, 

 I discovered it sitting in a cell nearly filled with honey. Later on I found 

 several cells containing larvse differing from those of Halictus and which 

 can hardly be other than those of Sphccodes. Finally I found in the autumn 

 a cell containing a dead specimen of a fully colored Sphccodcs pupa. It is 

 therefore proof that Sphccodcs is a cuckoo with Halictus." 



Nielsen calls attention to the fact that the parasitic habit of 

 Sphccodes explains the great variations in size, puncturation, etc., 

 which have led taxonomists to multiply species in the genus. He 

 found that poorly nourished individuals are often only half the 

 size of well-fed specimens. Perkins had previously noticed that 

 small forms of Sphccodes live with small Halicti and vice versa. 

 Sichel, after studying 3,200 specimens of European Sphccodcs, 

 decided that they represented only three species. He sent 600 

 other specimens which he referred to two species to Foerster, who 

 claimed that he could distinguish some 150 species among them, 

 but wisely refrained from publishing descriptions. Similar varia- 

 tions are, of course, frequent in other parasitic insects, notably in 

 Mutillidse and in Ceropalcs. 



The aggressive behavior of the female Sphccodcs, which was 

 also observed by Nielsen, suggests that she may enter Halictus cells 

 which are already completed and destroy the egg of the host, so 

 that her own progeny will not have to compete with the lawful 

 owner of the bee-bread, as in the case of Stclis and the other para- 

 sites studied by Graenicher. At any rate our knowledge of the 

 behavior of Sphccodes is in need of further careful investigation. 



When commenting on the difficulties encountered by the taxo- 

 nomic student of the bees, I omitted one of the greatest, viz., that 

 presented by the numerous parasitic genera. In many cases these 

 are known to be very closely related to the genera of their hosts, a 

 fact which was noticed even by the early investigators, although its 

 full significance became apparent only in the course of time, with 

 the constant discovery of new species and genera in all parts of the 

 world and with changes in the interpretation of general biological 

 phenomena. The whole matter is so interesting that I may be 

 pardoned for introducing some historical considerations. 



The more than a century devoted by entomologists to the study 

 of bees may be conveniently divided into a pre- and a post- 



