Tussock Moth Outbreak Resulting in Tree Defoliation

Mountainair and Sandia Ranger Districts

Albuquerque, NM, September 14, 2022 – If you are viewing brownish-red discoloration of trees on the eastern slopes of the Manzano Mountains or the eastside of the Sandias, it may be the result of defoliation from the Douglas-fir tussock moth. The defoliation occurs within mixed conifer stands affecting Douglas-fir, white fir trees and even some ponderosa pine.

Two Douglas Fir trees with bare lower branches from defoliation

Evidence of defoliation. USDA Forest Service photo.

To the casual observer, the affected trees may appear to be dying, but those brown branches signal the outbreak of the Douglas-fir tussock moth, a native defoliator whose larvae (i.e., caterpillars) feed on the foliage of a variety of trees species. The caterpillar feeds on the previous year’s needles often resulting in defoliation, which weakens affected trees and may be followed by subsequent attacks by bark beetles that may kill the tops or entire trees.

Douglas-Fir tussock moth are experiencing a rise in population on the Mountainair and Sandia Ranger Districts. The caterpillars have thousands of tiny hairs covering their bodies. The female moths, egg masses, and cocoons also have hairs, which can cause tussockosis, an allergic reaction from direct skin contact with the insects themselves or their airborne hairs.

Symptoms may include itchiness, skin rashes, skin irritation, watery eyes, runny nose, and sneezing. More severe reactions, though less common, include blisters, coughing, shortness of breath, wheezing, and chest tightness. Tussockosis severity may vary between individuals, by the amount of exposure, and the level of the outbreak.

Everyone should avoid touching or handling this insect, in any of its forms! If contact does occur, immediately wash the area of exposure. If symptoms become severe or problematic, immediately seek medical care.

Tussock Moth caterpillar up close white and hairy

Tussock Moth caterpillar. USDA Forest Service photo.

Forest Service Entomologist Dr. Steven Souder said, “Trees may recover from early infestations which can look quite dramatic; however, multiple seasons of repeated defoliation can predispose trees to disease and other insects causing tree mortality.”

Trees that regrow their needles will put out new shoots over the summer that will appear more bronze than gold in the fall. In old trees or trees stressed by the elements, the caterpillar can hasten mortality, but may survive this annual harbinger of summer in the southwest.

The Forest Service conducts annual aerial surveys over the summer months to track the damage done by Tussock Moths and other insects in New Mexico national forests.

Review the Tussock Moth flyer posted at trailheads: "Do Not Touch: Allergic Reaction May Occur".