ANNAPOLIS, MD (June 6, 2025)– The Maryland Department of Agriculture has announced populations of spring hardwood defoliating caterpillars have reached outbreak levels in Garrett, Allegany, and Washington Counties, causing widespread leaf damage to hardwood trees, especially oaks. While trees are not dead, over the next few weeks affected trees will take a similar appearance to that of trees in the winter. Additionally, the caterpillars causing the leaf damage will be a major nuisance for property owners and will produce large amounts of silk and frass (caterpillar droppings) falling on anything underneath the trees they are feeding on. Caterpillars will remain in the affected areas until mid-June when they begin to pupate in the soil. Maryland Department of Agriculture Forest Pest Management, Maryland Park Service, and Maryland Forest Service are working together to map and monitor this region-wide outbreak.
Areas in which defoliation will be most visible include the following:
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In Garrett County, near Grantsville and along the ridgetop of Meadow Mountain from Deep Creek Lake to Keyser’s Ridge, extending north into Pennsylvania.
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In Allegany County, in Green Ridge State Forest along the ridgetops of Town Hill, Green Ridge, and Polish Mountain.
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In Washington County, on the west side of South Mountain, visible from Annapolis Rock and Black Rock vistas.
The defoliation is being caused by a native “looper complex”; multiple species of geometer caterpillars, also known as “loopers” or “inchworms” that emerge in spring to feed on new leaves. Geometer caterpillars can be distinguished from other caterpillar types by the unique way they move; the caterpillars “inch” forward by making a small loop with their bodies. In Garrett County, the main species causing damage is the fall cankerworm (Alsophila pometari). In Allegany and Washington Counties, the majority of the damage is being caused by half wing geometer (Phigalia titea), linden looper (Erannis tilaria), and fall cankerworm. The invasive spongy moth caterpillar (Lymantria dispar dispar) causes similar defoliation, but is not contributing to this outbreak.
Trees affected by defoliating caterpillars are not dead and will grow a new set of leaves by late June-early July, however, repeated looper defoliation, especially in stressed trees on high ridgetops, can cause mortality. Natural predators of these caterpillars including birds, Calosoma beetles, parasitic wasps, and various naturally occurring diseases usually cause high populations to crash before major tree mortality occurs. These predators, parasites, and diseases have been seen at all outbreak sites by the department’s Forest Pest Management staff.
For more information on looper caterpillars and other forest pests in the State of Maryland, please visit the Maryland Forest Pest Management website at mda.maryland.gov.
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