HONEY-DEW 169 



when the tertiary deposits of (Eningen and Eadoboj were 

 laid down, Dr. Heer of Zurich has shown that at least 

 eighty- three distinct species of ants already existed ; and 

 the number that have left no trace behind is most probably 

 far greater. Some of the beetles and woodlice which ants 

 domesticate in their nests have been kept underground so 

 long that they have become quite blind that is to say, 

 have ceased altogether to produce eyes, which would be of 

 no use to them in their subterranean galleries ; and one 

 such blind beetle, known as Claviger, has even lost the 

 power of feeding itself, and has to be fed by its masters 

 from their own mandibles. Dr. Taschenberg enumerates 

 300 species of true ants'-nest insects, mostly beetles, in 

 Germany alone ; and M. Andre gives a list of 584 kinds, 

 habitually found in association with ants in one country or 

 another. Compared with these singular results of formi- 

 can selection, the mere production or further development 

 of the honey-tubes appears to be a very small matter. 



But what good do the aphides themselves derive from the 

 power of secreting honey-dew ? For we know now that 

 no animal or plant is ever provided with any organ or 

 part merely for the benefit of another creature : the 

 advantage must at least be nratual. Well, in the first 

 place, it is likely that, in any case, the amount of sugary 

 matter in the food of the aphides is quite in excess of 

 their needs ; they assimilate the nitrogenous material of 

 the sap, and secrete its saccharine material as honey-dew. 

 That, however, would hardly account for the development 

 of special secretory ducts, like the honey-tubes, in which 

 you can actually see the little drops of honey rolling, under 

 the microscope. But the ants are useful allies to the 

 aphides, in guarding them from another very dangerous 

 type of insect. They are subject to the attacks of an 

 ichneumon fly, which lays its eggs in them, meaning its 



