358 



PSYCHE. 



{June, 1902 



dakotensis, half siibsericea. For the 

 rest, if F. dakotensis has no slaves, it 

 builds mounds often bearing a deceptive 

 resemblance to those of F. exsectoides, as 

 also at least their workers have some 

 similarity with those of the latter, with 

 the exception that their appearance is 

 more delicate, the head being rounder, 

 smaller and with less concavity of the 

 occiput. Here too the slaves are, at least 

 so far as may be determined from seven 

 instances, in an inverse proportion to the 

 number of the "lords." 



The greatest irregularity of nest 

 structure is to be noticed with F. siibser- 

 icea Say, the auxiliary of F. nibiciinda 

 and F. dakotensis^ active, fleet-footed, 

 but cowardly, at least if alone. Yet not- 

 withstanding the great variety, four prin- 

 cipal kinds of nest structure may be dis- 

 tinguished. Passing along the edge of 

 a forest, our attention may be suddenly 

 arrested by a bare spot in the grass. 

 At the same time there are to be noticed 

 a number of apertures, through which 

 the somewhat silky inmates effect an 

 incredibly sudden retreat. This is one 

 of their usual methods of nest construc- 

 tion. Another method not less charac- 

 teristic is the one utilized now and then 

 in the mixed colonies of F. riibicunda ^ 

 siibsericea and dakotensis r^ siibsericea. 

 On some slight elevation along the road 

 arises an oblong, moderately sized hil- 

 lock, topped by a piece of rock or a 

 branch of a tree. The numerous en- 

 trances of the nest are all situated 

 under this protecting roof, where during 

 May and June may be found the queens 



and cocoons which, however, disappear 

 with marvellous rapidity upon the re- 

 moval of their guardian portal. More- 

 over, mounds may be perceived here 

 and there, but neither as large nor of 

 the same shape as those of F. obscuripcs 

 and F. exsectoides. Finally, small col- 

 onies generally hide their establishments 

 beneath stones. 



Whilst the subsericea-nests, at least 

 hereabouts, are never found in decaying 

 logs, these are precisely the habitations 

 of Formica subaenescens Em., so called 

 from the appearance of its abdomen. 

 When enslaved by Polyergiis bicolor 

 Wasm., which in consequence of its 

 sickle-shaped mandibles is unable to 

 excavate, they entirely determine the 

 structure of the latter's nest. Yet it is 

 not without interest to notice that these 

 nests, as will be mentioned later on, with 

 regard to .some species of Camponotus, 

 Larius, Stenamma etc., are in communi- 

 cation with the earth, whither tiieir 

 inmates retire during the extremes of 

 cold and heat. Concerning the rather 

 insignificant structures of the other five 

 species occurring in this region, namely 

 F. pergandci Em., F. nitidiventris Em., 

 F. fiiscata Em., F. schaiifiissi Mayr and 

 F. incerta Em., it may suffice to remark, 

 that they usually occur at the edge of 

 fields or on hillsides, being ground 

 nests and having their entrances under 

 stones and logs. 



In comparison, therefore, with the 

 ants of Europe the exterior structure of 

 American formicaries is somewhat insig- 

 nificant, so that Forel justly avoided 



