This insect was discovered in Connecticut in 1985 and has spread rapidly to both cultivated and forest hemlocks.
Adelgids are small, soft-bodied insects that are closely related to aphids.
They have piercing-sucking mouth parts, which are inserted to remove plant sap for food. The HWA feeds primarily on young branches causing cessation of tree growth, discoloration and premature drop of needles, the dieback of branches and possible death of the tree in as little as one year. The females are oval, blackish-grey, about 2mm in length and serve as the overwintering stage. May. The presence of the egg sacs offers the most visible diagnostic evidence of an HWA infestation. Some of the adults are wingless and remain on hemlock for a second generation, while the winged forms may fly to nearby hemlocks or spruces.