The spatial distribution and environmental triggers of ant mating flights: using citizen-science data to reveal national patterns

Many ant species produce winged reproductive males and females that embark on mating flights. Previous research has shown substantial synchrony in flights between colonies and that weather influences phenology but these studies have been limited by sample size and spatiotemporal scale. Using citizen science, we gathered the largest ever dataset (>13,000 observations) on the location and timing of winged ant sightings over a three-year period across a broad spatial scale (the United Kingdom). In total, 88.5% of winged ants sampled were Lasius niger. Observations occurred from June to September with 97% occurring in July/August but exact temporal patterns differed substantially between years. As expected, observations within each year showed a small but significant northward/westward trend as summer progressed. However, the predicted spatiotemporal synchrony was far less apparent; observations were not significantly spatially clustered at national, regional or local scales. Nests in urban (vs. rural) areas and those associated with heat-retaining structures produced winged ants earlier. Local weather conditions rather than broad geographical or seasonal factors were shown to be critical in the timing of winged ant activity, presumably to optimize mate finding and to minimize energy consumption and predation. Temperature and wind speed, but not barometric pressure, were significant predictors of observations (positively and negatively, respectively); winged ants were only observed at temperatures >13 °C and wind-speeds <6.3 m-1. All days with a mean daily temperature >25°C had observations. Intriguingly, changes in temperature and wind speed from the day before flight peaks were also significant. We conclude that: (1) spatiotemporal synchrony in flights is lower than previously thought for L. niger, (2) local temperature and wind are key predictors of flight phenology; and (3) ants appear able to determine, at least in a limited way, if weather is improving or deteriorating and adjust their behaviour accordingly