Intraspecific usurpation of incipient fire ant colonies

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Abstract
Brood raiding, or reciprocal stealing of brood, is common among incipient colonies of the fire ant Solenopsis invicta. Paradoxically, workers from a colony that loses its brood during a raid often abandon their nest and join the winning colony. Queens abandoned by their workers may then migrate from their original nest site and attempt to forcefully usurp another incipient colony by displacing that colony's queen or queens. This study examined factors that influence the success of usurpation attempts. Queens attempting to usurp a nearby colony after laboratory brood raids were successful in less than 30% of trials. Usurpation attempts were more successful if workers familiar to the migrating queen were present in the nest, as would happen if a queen were to find the colony to which her workers had moved. Cross-fostering experiments showed that this effect was due to familiarity rather than relatedness. Usurpation attempts were less successful if they were delayed by 16 h. The probability of usurpation success was not reduced by doubling the number of defending workers in the invaded colony. However, colonies founded by three queens were almost always able to resist usurpation attempts. These results support the hypothesis that workers abandon their natal colony after losing a brood raid to increase the likelihood that their queen can usurp the colony to which they migrate. These results also provide the first evidence that colonies of ants founded by several queens are better able to resist usurpation attempts than colonies founded by a single queen

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