Why do spiders balloon? a review of recent evidence

Abstract

Spider aerial dispersal, also known as ballooning, is a behavior that enables spiders to escape adverse conditions and colonize isolated habitats, making it crucial for species persistence. This systematic literature review delves into this phenomenon through the lens of three of Tinbergen's four questions for analyzing animal behavior: mechanism, development, and function. We included 130 studies in our analysis, from 1939 to 2024, with particular attention paid to works from the last two decades. We explored two primary theories explaining the mechanisms behind ballooning and concluded that the aerodynamic theory plays the most important role. Additionally, factors such as conspecific density, food availability, habitat heterogeneity, and individual experience significantly influence spiders' decisions to disperse, underlining the highly context-dependent nature of dispersal strategies. The primary evolutionary driver of aerial dispersal in spiders is the need to escape unfavorable conditions, tied to adapting to environmental variability and habitat changes. These findings illustrate the complexity of spider dispersal behavior. The conservation implications of ballooning are also considered, highlighting how this behavior helps spiders respond to habitat fragmentation and environmental change, while also addressing how dispersal may be impacted by these global change drivers. By integrating mechanistic, developmental, and functional perspectives, this review provides a comprehensive understanding of the factors influencing spider ballooning and evidences the lack of studies in non-agricultural environments on dispersal strategies, their function and their evolution. Future research in less-explored habitats may uncover new information that could redefine the general patterns of ballooning behavior observed thus far.