Larger Workers Are More Likely to Be Drifters in the Bumble Bee Bombus impatiens

Abstract

Worker drift, a behavior where individuals leave their natal colony to reside in another conspecific colony, has been given both adaptive and maladaptive explanations in social hymenopterans. This behavior is typically attributed to disorientation in commercially managed honey bees where it can increase disease transfer and negatively impact colony fitness. Alternatively, it has been shown that bumble bee and honey bee drifters are producing males in the foreign colony. This suggests individuals may be escaping policing in their natal colony in order to increase their own fitness. Drifters act as social parasites by not working in the foreign colony and reproducing despite potential retaliation. The mechanisms that allow drifters to go undetected in the foreign colony are still unclear. In this study, we further explore the hypothesis that drift is a reproductive strategy for individual workers in the bumble bee, Bombus impatiens Cresson, 1863, by looking at its relationship to worker size. We predict that larger workers’ fertility will increase their propensity to drift. We found that larger workers are more likely to drift and those drifters are larger than both in-nest workers and foragers from their natal colony. This result provides further support that drifting in bumble bees functions as an alternate reproductive strategy.