THE AMERICAN MUSEUM JOURNAL 

 SOCIAL PARASITISM AMONG ANTS. 



]N an article published in last year's volume of the 

 Bulletin of the American Museum, the author 

 called attention to the occurrence of certain very 

 diminutive females, or queens, in a species of ant 

 {Formica microgyria) from Colorado and Utah. 

 Unexpected light was thrown on this interesting reduction in the 

 size of the queen by a recent study in the Litchfield Hills (Conn.) 

 of another ant (F. difjicilis) which is known to have similar 

 queens. Several peculiar mixed colonies were found, each con- 

 sisting of a fertile queen of F. difjicilis, either singly or accom- 

 panied by a few young workers, living in colonies of another ant 

 {F. incerta). Afterward the fact was established, both by 

 observation of the natural colonies and by keeping the ants 

 in artificial nests, that the difjicilis queen, being too small to bring 

 up her own colony, enters a queenless colony of F. incerta, and 

 then turns over her first batch of young to be brought up by 

 the incerta workers. As the difficilis colony grows to be more 

 and more populous, it gradually emancipates itself from the 

 incerta and finally becomes a pure difjicilis colony, the workers 

 of which are as bold and pugnacious as the queen and her first 

 offspring were timid and conciliatory. 



These observations show that F. difficilis is a true cuckoo 

 ant, a temporary parasite. All the mixed colonies of ants have 

 hitherto been tacitly regarded as permanent unions or consocia- 

 tions of two species, like the slave-making ants and their slaves, 

 or auxiliaries. The case of F. difficilis throws light on a whole 

 series of mixed colonies which have been called abnormal or 

 accidental, merely because they have not often been seen, like 

 the mixed colonies of Aphcenogaster tennesseense and A. fulvum; 

 Formica exsectoides and F. subsericea; F. dakotensis and F. 

 suhsericea; and the European as well as the American F. rufa and 

 F. fiisca with their varieties. In all these cases it is highly prob- 

 able that we are concerned with a normal temporary parasitism 

 of one species of ant on another. The species of Formica which 

 exhibit this method of founding their colonies all belong to the 



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