Pemphigus obesinymphae is a North American social aphid that is found in clonal groups inside of galls on poplars. Larval soldiers defend their domicile by attacking natural enemies. Previous work showed that soldiers also leave their galls in large numbers and "intrude" upon other clones, where they become "cheaters" that do not contribute to defense but rather exhibit accelerated growth rate relative to the natal clone. We have employed microsatellite markers to test the hypothesis that clones occur in spatial groups on poplars, in which case the intruder strategy would be more mutualistic than exploitative. However, we have found little evidence of such kin structure. We still do not have a complete explanation for such a high degree of exploitation in this social insect.