HWA is immobile for most of its life. However, there is a small period of time right after it hatches from the egg when it can be transferred from tree to tree. This is called the “crawler” stage. When it’s in the crawlers stage, it can be passively distributed many ways such as by wind or by birds who have landed on an infested tree and carry crawlers to another hemlock. Transplanting of infested trees can speed up their spread.
Returning NC's Hemlocks to Long-Term Health