The hemlock woolly adelgid (HWA), a tiny sap sucking insect related to aphids, is causing widespread death and decline of hemlock trees in the eastern U.S.. Two species of silver flies from the Pacific Northwest are showing promise as potential biological controls of hemlock woolly adelgid in the East: Leucopis argenticollis and Leucopis piniperda. Both species are abundant predators on western hemlock adelgids, but it was not known if they would perform as well on the hemlock woolly adelgids introduced from Japan to the eastern U.S., where they are devastating pests of hemlock trees. In laboratory tests, the flies developed on eastern adelgids as well as they did on western adelgids. Scientists also released the silver flies onto mesh-enclosed hemlock branches infested with adelgids in Tennessee and New York, where they successfully reproduced. The number of fly offspring increased with increasing adelgid density, which is a good sign for their ability to control adelgid populations. The research demonstrates that these predators can feed and develop on hemlock pest adelgids in the eastern U.S. and that they are able to tolerate environmental conditions at the southern and northern ends of the area invaded by the Japanese adelgids. Efforts are underway to release these flies to establish them in the East and evaluate their ability to control this invasive pest.