500 



nests which always display tlie architecture of the working ant (slave 

 or host), and have no further interest for us here. When Polyergus 

 rufescens seizes Formica rufibarhis and keeps it as its slave, its nest 

 resembles a larger nest of that species ; if, on the other hand, it enslaves 

 Formica fusra, its nest looks like the nest of Formica fu-wa, because 

 the so-called slave or auxiliary ants are the only builders. 



The case appears to be somewhat different in the rare, natural, for- 

 tuitous mixed colonies [Formica pratensis or irimcicola or exsecta, svith 

 Formica fusca; Tapinoma erraticnm with Bothriomyrmex meridional is) 

 discovered by me (Fourmis de la Suisse), as well as in Formica san- 

 guinea Latr., which almost always keep slaves, but notwithstanding 

 also work themselves. Here the nest assumes a mixed architecture, 

 as both si)ecies of ant work on it, each in accordance with its instinc- 

 tive art. And yet they do not interfere with each other. Each species 

 understands how to combine its work harmonionsly 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 pratcnsis, 

 which work more like carpenters with their little branches and cross- 

 pieces. Fusca unites the wooden rafters of pratcnsis by means of moist 

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

 mixed colonies to be founded between Formica sanguinea and F. pra- 

 tensis, etc., have even discovered naturally established colonies of these 

 two latter species, and have investigated their mixed architecture. 



9.— MIGRATORY NESTS. 



Belt (The Naturalist in Nicaragua, 1S74) was again the first to dis- 

 cover the hitherto -unknown nest of the American migratory ants 

 [Fciton). He found in the forest an immense ant ball, from wliich 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 

 ha<l been with regard to the other discoveries 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. Wilhclm Miil- 

 ler, who was residing at that time at Blnmenau with his brother, in 

 this question. Dr. W. Miiller has published the results of his very 

 interesting observations in the tirst volume of Kosmos (1886, p. 81: 

 Observations on Migratory Ants). That which bears upon onr subject 

 may be summed up as follows: The larger species of Ecifon, which have 

 eyes [hamatum F., foreli Mayr, quadriglumis IIalid. [=^legionis Sm. 

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

 wandering life and merely occupy with their extremely numerous colo- 

 nies 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 etherized state 5,000 cubic centimeters). 

 Thelarvic and pupie first collected by Dr. W. Miiller and examined by me 



