WHEELER— THE PARASITIC ACULEATA. 3 



pollenation of flowering plants, themselves a group of organisms 

 of recent origin. As manifold morphological expressions of this 

 adaptation attention has often been called to the peculiar modifi- 

 cation of the mouthparts for extracting nectar from flowers, the 

 singular branched hairs of the body and modification of the hind 

 legs or hairs on the venter in the female for carrying pollen, and 

 the highly developed visual and olfactory organs. 



On the side of the instincts there are, further, the marvelous 

 habits of nidification which have aroused the admiration of all stu- 

 dents since the days of Reatimur. Still the general activities of the 

 female bee — the male is, of course, an ethological nonentity as in 

 other Aculeates — are strangely uniform in their general outlines : — 

 the visiting of flowers, mating, nidification, provisioning the nest 

 with pollen and honey, oviposition. But different species visit dif- 

 ferent flowers and build their nests in different places and of 

 different materials. All this is true of perhaps 80 per cent, of the 

 thousands of species, but a considerable number — between 15 and 

 20 per cent., representing fully 70 genera — have become parasitic 

 and have therefore ceased to collect pollen and nectar or to con- 

 struct and provision nests, but instead seek out the nests of other 

 bees and oviposit in their cells, with the result that the larvae reach 

 maturity by devouring the provisions so carefully stored for their 

 own offspring by more industrious mothers. 



This peculiar habit has profoundly modified the structure of the 

 parasites. Their mouthparts have not been affected to any extent 

 because these bees still visit flowers assiduously for food, but the 

 collecting apparatus has atrophied and the hairs on the body and 

 appendages have been completely or almost completely lost, so that 

 the species have sometimes been placed in a group by themselves 

 called Denudatas. Other peculiarities are also manifested. The 

 loss of the collecting apparatus, which is one of the most striking 

 secondary sexual characters of the female bee, excepting in the 

 Prosopidinse, which swallow the pollen instead of collecting it on 

 their hind legs or venter, has brought about a close resemblance of 

 the sexes to one another. In a few cases the female has even taken 

 on a male secondary sexual character, as in the genus Androgynella, 

 recently described by Cockerell (1918). It comprises two species. 



