any of various homopterous insects of the family Adelgidae, as Adelges abietis (spruce gall aphid) and Pineus pinifoliae (pine leaf aphid), that feed and form galls on conifers.
Hemlock woolly adelgid – Wikipedia
Landscape: Hemlock Woolly Adelgid | UMass Center for Agriculture
Adelgidae – Wikipedia
What are the impacts of Hemlock Woolly Adelgid? – Hemlock Woolly Adelgid