Photo by urbpan. Location: Forest Park, Springfield, Mass.

Urban species #348: Hemlock Woolly Adelgid Adelges tsugae

This insect spends most of its life hidden in a fluffy white shelter. It sucks the fluid from the needles of hemlock trees, and it is believed that as it feeds it introduces a toxic substance into the tree. Every plant has sap-sucking pests that feed on them, and most are not seriously damaging. An infestation of these hemlock woolly adelgid can cut the lifespan of an eastern hemlock down from hundreds of years to less than ten. The Asian hemlocks that the insect feeds on in its native range developed resistances that allow the trees and adelgids to coexist.

Adelgids are close relatives of aphids. Like some aphids, hemlock woolly adelgids are all female, and several generations are born in a single year. In the short time that the insects are mobile, they are carried from tree to tree by animals or by the wind. Adelgids have fully infested the hemlocks in all counties of southern New England, as well as the areas around New York CIty, Philadelphia, Washington D.C. and New Jersey. It's possible that the adelgid affects urban trees more severely because they are already weakened by pollution and other stresses. Methods to control the infestation include saturation of individual trees with pesticide, and the introduction of predatory beetles.