The key to killing the HWA is to catch it early and act quickly. It's already well established in the Great Smoky Mountains, where Rhea and others are trying to stem the spread of the bugs.

　　HWA multiply quickly: All of the insects are females that reproduce asexually (无性地), laying several hundred eggs a year. When they get to the nymph, or crawler, stage, they are dormant from about June until October, after which they emerge and establish themselves on trees.

　　Winds and birds and other animals spread the crawlers through the forest.

　　HWA crawlers feed on the new growth of hemlocks by piercing the twigs that hold the branches, sucking the sap, and injecting toxic saliva. The needles turn from a deep green to a grayish green and eventually die, depriving the tree of nutrition from photosynthesis.

　　An infected tree usually dies within five years of initial attack. Infection is signaled by either a white, cottonlike material that appears along a tree's twigs or by the "baldness" of a tree's upper branches.