Hello, Aaron. When hemlock woolly adelgid (HWA), is in its crawler life stage, it is possible for them to be transported onto unrelated plants, or they could fall onto the soil. However, they are not able to survive without hemlock, so without a suitable host, they could die within 24hours or in a few days depending on if they are exposed to the sun. There is also a winged adult stage known as sexupara and they can fly to different plants (mid-summer), but in order to survive they need to find their host, which would be the tigertail spruce. Unless you have planted a tigertail spruce, you should not have to worry about HWA spreading through the soil or onto other plants besides hemlock.

Best,

Carrie

Oregon IPM Center