Invasive species change ecosystems and the economic services such ecosystems provide. Optimal policy will minimize the expected damages and costs of prevention and control. We seek to explain policy outcomes as a function of biological and economic factors, using the case of Hawaii to illustrate. First, we consider an existing invader, Miconia calvescens, a plant with the potential to reduce biodiversity, soil cover, and water availability. We then examine an imminent threat, the potential arrival of the Brown treesnake (Boiga irregularis). The arrival of the snake in Guam has led to native bird extirpations, power outages, and health costs.