It is suspected that birds may play a role in the dispersal of this insect along with hurricanes and undoubtedly humans. Spread within Connecticut in 1986 was into distant residential areas, all where bird feeders were being maintained year around. The HWA feeds on the young branches and twigs of the host, usually near the needles.
All stages suck the sap from the host.
The HWA also probably injects a toxin into the hemlock along with its saliva during feeding. On the east coast, HWA damage has been the most severe. It can also cause yellowing, desiccation, and death of the older needles. In severe infestations, main limbs can be killed back the first summer and death can occur in as short a period as one year. It is a threat to both ornamental and forest hemlocks along the Atlantic Coast, whereas western forest hemlocks are seldom severely injured in the Northwest.