Crop pests are among the greatest threats to human livelihoods and wellbeing. Some of the worst offenders are invasive species, accidentally or thoughtlessly spread around the world by people. Once these pests are well established, it can be too late to tackle them. We’re working on improving early response to invasions in developing countries by designing rapid forecasting techniques for the most pests most likely to invade. For example, the Fall armyworm is a moth whose caterpillars attack a wide range of crops in the Americas. It has recently spread to Africa, with potentially devastating results for millions of farmers. Our recent modelling work contributed to an evidence note commissioned by the UK Department for International Development, and led by collaborators at CABI. The report finds that each year the caterpillars could destroy between 8 and 20 million tonnes of the 39 million tonnes of maize that Africa produces, at a cost of up to US$6,187 million.