The elm zigzag sawfly (Aproceros leucopoda) is now established in several places in North America. This non-native forest pest can be a threat to elm species and hybrids and is capable of large defoliation events. Will it turn into a full-blown invasive species, or simply co-exist with native herbivores in natural and urban forests? At this point, we don’t know. A new review highlights elm zigzag sawfly biology, ecology, and management strategies in the U.S.