Free ride without raising a thumb: A citizen science project reveals the pattern of active ant hitchhiking on vehicles and its ecological implications

Species hitchhiking on human transportation objects such as vehicles can facilitate long-distance dispersal of organisms, allowing increased probabilities of successful biological invasions. In Taiwan, there have been observations of ants actively moving onto motor vehicles (defined as 'ant hitchhiking' hereafter), yet no study has explored this phenomenon. Here, we provide the first qualitative and quantitative report on ant hitchhiking behaviour using citizen science data. From 2017 to 2023, 52 cases of ant hitchhiking on vehicles were reported (at least three cases with queen[s] and another eight cases with brood), attributed to nine species. Seven of the nine species were exotic/invasive. Arboreal or semi-arboreal ant species, particularly the exotic black cocoa ant (Dolichoderus thoracicus), accounted for over half of the reported cases. The parking duration of the vehicles on which the ants hitchhiked ranged from several hours to over a month (30 cases occurred within a day). Moreover, more cases were reported in the warmer seasons (spring and summer) than in the colder seasons (fall and winter). To our knowledge, this study represents the first effort to profile active ant hitchhiking on vehicles. We encourage future studies to examine the abiotic and biotic factors that determine the success of hitchhiking events to better predict the spread of exotic/invasive ants and to develop effective management strategies for preventing their biological invasions. We characterised ant hitchhiking incidences, defined as ants actively moving onto motor vehicles, through a 7-year citizen science project to inform strategies for mitigating ant invasions resulting from hitchhiking. A total of 52 cases were reported/analysed. Nine ant species were recorded, with seven being exotic/invasive. Functional group analysis indicates most of the species were arboreal or semi-arboreal. Interplays of several factors, including ant population density, life history traits associated with arboreal/semi-arboreal ants, season, and vehicle parking habit, may determine the occurrence of ant hitchhiking. image