ants' nests. 375 



well as in Formica sangiimea^ Latr., which almost always keeps 

 slaves, but notwithstanding also work themselves. Here the nest 

 assumes a mixed architecture, as both species of ant work on it, 

 each in accordance with its instinctive art. And yet they do not 

 interfere with each other. Each species understands how to com- 

 bine its work harmoniously with that of the other, Although the 

 methods of the two are often very different, as, for instance, 

 with the mason ants, Formica fusca and Formica praiensis^ which 

 work more like carpenters with their little branches and cross- 

 pieces. Fusca unites the wooden rafters of pratensis by means of 

 moist earth, and the whole lasts very well. I have also caused 

 many artificial mixed colonies to be founded between For^nica 

 sanguiiiea and F. pratensis^ etc., have even discovered naturally 

 established colonies of these two latter species, and have investi- 

 gated their mixed architecture. 



9. — Migratory Nests. 



V>q\\. {The Naturalist in Nicaragua^ 1874) was again the first 

 to discover the hitherto unknown nest of the American migrator^ 

 ants ( Eciton). He found in the forest an immense ant ball, from 

 which all the robber columns issued, and in which all the brood 

 lay. Here was a genuine nomad nest, a living nest without a 

 house. Sceptical as we had been with regard to the other discov- 

 eries of the genial Belt, we remained so respecting this one, too, 

 until I succeeded, in the year 1885, in interesting Fritz Miiller's 

 younger brother, Dr. Wilhelm Miiller, who was residing at that 

 time at Blumenau with his brother, in this question. Dr. W. 

 Miiller has published the results of his very interesting observations 

 in the first volume of Kosmos (Observations on Migratory Ants^ 

 1886, p. 81). That which bears upon our subject may be summed 

 up as follows : The larger species of Eciton^ which have eyes 

 (hamatum, ¥.,foreli, ^^yr, quadriglumis, Halid. \_ = legionis, Sm. 

 = lugubre^ Roger], etc.) do not build or excavate any nests. They 

 live a wandering life and merely occupy with their extremely num- 

 erous colonies spacious, naturally sheltered places, such as hollow 

 trees or shrubs, in which they live rolled up together in immense 

 clusters (one cluster of ants and brood, measured by Dr. W. 

 Miiller, which did not compose half the colony, measured in an 



