Managing biological invasions is one of ecology’s most difficult challenges. One controversial approach is the use of biocontrol agents, which involves transplanting an invasive’s natural enemies in an effort to control its spread. In this episode of Field Talk, Dean Pearson, a research ecologist with the U.S. Forest Service, talks about a grassland community in western Montana where a biocontrol insect has been introduced to control an invasive weed. His paper in the September issue of Ecological Applications shows that even the most carefully selected biocontrol agents can have complex and detrimental indirect effects on the community.