Hemlocks in southern Appalachia – more specifically, Great Smoky Mountains National Park – received a surprising ally in the battle against hemlock woolly adelgid (HWA). Unusually frigid temperatures that settled in the region this winter appear to have helped abbreviate the life cycle of the pest, which completes part of its development in winter, protected by its white, woolly silk. Snow cover also can help shelter the pest.

A prolonged period of below-zero temps at higher elevations of the park appears to have killed several populations – many of which have managed to survive and rebound in past winters. Last year’s drought encouraged growth of the pest population, but the combination of dry weather and sub-zero temperatures has taken its toll.

HWA was confirmed in Great Smoky Mountains National Park in 2002, where it thrived until the polar vortex of 2014-2015 stemmed its spread. It’s unlikely the pest will be completely eradicated, but efforts by the National Park Service – including some spraying and the introduction of predatory beetles – is aimed at keeping populations in check.

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