Abstract: An experimental field study demonstrates that mature colonies of Myrmecocystus mimicus Wheeler, 1908 raid neighboring conspecific small colonies without preceding territorial tournament actions. We also report a total of 17 complete brood raids that did not originate from territorial tournaments, collected during 10 field research seasons. The number of captured brood and booty varied greatly: 6 - 137 larvae, 9 - 152 pupae, 0 - 4 callows, 0 - 23 honeypots. We also observed raiding ants transporting liquid food in their crops when they left the raided nest (49 - 409). Most likely, this food was solicited from honeypots inside the foreign nest. In general, the captured booty during these raids is considerably smaller than that retrieved during raids that originated from tournaments. The socio-genetic analyses provided evidence that workers eclosing from raided brood become part of the work force of the raider colony. This was shown for Myrmecocystus mimicus and M. depilis Forel, 1901. In M. depilis, we confirm previous findings by Kronauer & al. (2003) of interspecific raiding (i.e., M. depilis raids M. mimicus but not vice versa). In addition, we provide genetic evidence for facultative polygyny in M. mimicus, and obligatory monogyny and occasional polyandry in M. depilis.