The role of climatic similarity and bridgehead effects in two centuries of trade-driven global ant invasions

International trade continues to drive biological invasions. We investigate the drivers of global nonnative ant establishments over the last two centuries using a Cox proportional hazards model. We use country-level discovery records for 36 of the most widespread nonnative ant species worldwide from 1827 to 2012. We find that climatic similarity combined with cumulative imports during the 20 years before a species discovery in any given year is an important predictor of establishment. Accounting for invasions from both the native and previously invaded “bridgehead” regions substantially improves the model's fit, highlighting the role of spatial spillovers. These results are valuable for targeting biosecurity efforts.