Invasive plant species do more than harm agriculture and native species as they reshape landscapes. They also cause economic losses of more than $20 billion annually in the U.S. alone. Identifying where and how quickly invasive plants are spreading is critical to fighting an invasion. Scientists and land managers currently use on-site field surveys of population size, density or growth rates to obtain this information, which can be prohibitively expensive and labor intensive. Furthermore, invasive species are spreading so rapidly around the world that traditional methods have become untenable. New techniques are urgently needed to track invasive species more efficiently.