Tent caterpillars once again munching on the aspens

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By The Staff

Visitors and locals driving up NM 475 (the road to the Santa Fe Ski Basin) may notice something happening with aspen groves that create one of the most popular vistas on the Santa Fe National Forest.

To the casual observer, the aspens may appear to be dying. But those bare branches signal the return of the western tent caterpillars, native defoliators whose larvae feed on a variety of hardwood trees species. At least here in New Mexico, they seem to be particularly fond of aspen.

The caterpillar gets its name from the conspicuous “tent” it builds on branches and twigs. The silken shelter protects the larvae during molting. As they mature, the larvae disperse and continue feeding on leaves until it’s time to retreat into cocoons for their transformation into moths. The process takes a couple months after which the adults mate and the female moths lay the eggs that become next year’s caterpillars.

Forest Service Entomologist Dr. Andrew Graves said, “Although the defoliation can look quite dramatic, the trees often recover with limited tree mortality.” The good news is that, in most cases, the affected aspens will refoliate, putting out new shoots over the summer that will appear more bronze than gold in the fall. In old trees or trees stressed by disease, the caterpillar can hasten mortality, but most survive this annual harbinger of summer in the southwestern United States.

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