264 BRITISH BEES. 



their economy, but it may also be from o-r^Xt?, a little 

 column, in application to their cylindrical form. In 

 but few of the parasitical bees do we know the precise 

 nature of their transformations, I have therefore been 

 obliged to be silent upon this point of their natural 

 history, and I have nothing to state of its nature in 

 these, although I expect there is much uniformity with 

 but slight modifications in all. The species of this genus 

 are parasitical upon the Osmice ; thus the S. ph&optera 

 is found to infest the O. fulviventris, and the S. octo- 

 maculata intrudes itself into the nests of 0. leucomelana, 

 both of which occur tolerably abundantly near Bristol. 

 I have no doubt that the south-west and west of England, 

 if well searched, would yield many choice insects. 



It is singular that bee parasitism does not prevail 

 throughout all the genera of bees, some being subject to 

 it and others not. Thus the genera Colletes, Andrena, 

 Halictus, Panurgus, Eucera, Anthophora, Saropoda, 

 Megachile, Osmia, and Bombus have all parasites, 

 whereas the genera Cilissa, Macropis, Dasypoda, Cera- 

 tina, Anthidium, Chelostoma, Heriades, Anthocopa, and 

 Apis have none, as far as we yet know ; and some of the 

 genera of parasites frequent two or more genera indif- 

 ferently, whilst others are restricted to a single one; 

 also some of the species of the parasitical genera infest 

 indifferently several of the species of the genus to which 

 their parasitism is mainly limited ; other species have 

 a more circumscribed range and do not visit the nests of 

 more than a single species. What law may control all 

 these seeming anomalies we cannot discover, it may 

 possibly be scent that guides them, and this may con- 

 trol their parasitism by indicating the species they are 

 taught by their instinct to be most suitable from the 



