Individual variation in ballooning dispersal by black widow spiderlings: The effects of family and social rearing

Individual behavioral variation is ubiquitous across taxa and important to understand if we wish to fully use behavioral data to understand the ecology and evolution of organisms. Only recently have studies of individual variation in dispersal behavior become a focus of research. A better understanding of individual variation in dispersal behavior is likely to improve our understanding of population dynamics. In particular, the dynamics of critically small populations (endangered species) and large populations (pest species) may be driven by unique dispersal variants. Here we documented individual variation in the ballooning dispersal behavior of Western black widow spiderlings Latrodectus hesperus, an urban pest species found in superabundant infestations throughout cities of the desert Southwest USA. We found a great deal of family-level variation in ballooning dispersal, and this variation was highly consistent (repeatable) across time. Maternal egg investment was a poor predictor of this ballooning dispersal. Instead, we show that spiderlings reared in isolation are significantly slower to disperse than spiderlings raised in a more natural setting surrounded by full siblings. Thus, our study examines a widespread but poorly understood dispersal behavior (ballooning), and suggests urban pest population dynamics are likely driven by the interaction of variation in individuals, families and social environments.