ANTS AND THEIR GUESTS WASMANN. 459 



some light at least has been shed upon this interesting problem. 

 All investigators agree that the phylogenetic history of social para- 

 sitism and of slavery in ants does not represent a simple line of devel- 

 opment, but a immber of different, parallel lines independent of each 

 other. But upon the closer relations between social parasitism and 

 slavery the views deviate from each other. You will therefore excuse 

 it if here I follow only briefly my own train of thought, as I have 

 explained it more fully in the Biologisches Centralblatt, 1909.^ 



Let us begin with the dependent foundation of colonies and its 

 relation to social parasitism and to slavery in Formica. The orig- 

 inal method here also — as with ants in general — must have been the 

 independent foundation of colonies, as, for example, we find it to-day 

 m. the fusca group. Here the females (fig. 5a), after the marriage 

 flight, are able to found then* new colonies independently; that is, 

 without the help of the workers. How have social parasitism and 

 slavery arisen from this root ? The first step probably consisted in 

 the transition to an acervicolous life in the workers, through which 

 the colonies became richer in individuals and could control a larger 

 area surrounding their hills, as we see it in the rufa group. Thereby, 

 however, the opportunity was offered to the females to found their 

 new settlements with the help of workers of then' own species. As 

 a second step in the parasitic and dulotic direction then followed, 

 through this same means, in the females of the rw/a group, that they 

 abandoned the independent foundation of colonies and became de- 

 pendent upon the assistance of workers, therefore passing over to the 

 dependent foundation of colonies. It is in any case a remarkable 

 phenomenon that all parasitic forms of Formica, of the Old World as 

 well as of the New, are acervicolous and belong to the rufa group 

 or stand in nearest relationsliip to it. The latter is also true for the 

 dulotic sanguinea group, which is connected with the rufa group by 

 morphological transitions. In the rufa group we have, furthermore, 

 biological transitions from the facultative mode of social parasitism to 

 the obligatory. Formica rufa (fig. 2) and F. pratensis found their 

 colonies mostly with the assistance of workers of their own species, 

 only facultatively with strange auxiliary ants (F. fusca, fig. 4h). 

 With Formica truncicola (fig. 3), F. exsecta (fig. 4a and 56), and F. 

 pressilahris in Europe, as well as with Formica consocians and a series 

 of other North American forms discovered by Wheeler, the latter mode 

 of colony foundation is already obligatory. 



With several North American parasitic Formicas described by 

 Wheeler, as well as in our Formica exsecta (fig. 5h) and F. jyressilairis , 

 the small size of the females is striking and already represents a 

 further step in the advance to parasitic adaptation, wliile for example 



» Ueber den Ursprung des sozialen Parasitismus, der Sklaverei und der Myrmecophilie bei den Ameisen. 



