ANNAPOLIS, MD (June 6, 2025) ~ The Maryland Department of Agriculture has issued a warning about a recent outbreak of spring hardwood defoliating caterpillars in Garrett, Allegany, and Washington Counties. The caterpillars have caused widespread leaf damage to hardwood trees, particularly oaks, and are expected to continue their destructive feeding until mid-June.

According to the department, affected trees will take on a similar appearance to those in winter as they lose their leaves. In addition to the damage caused by the caterpillars themselves, property owners can expect to deal with large amounts of silk and frass (caterpillar droppings) falling from the trees.

The outbreak has prompted collaboration between the Maryland Department of Agriculture Forest Pest Management, Maryland Park Service, and Maryland Forest Service. Together, they are working to map and monitor the affected areas.

The most visible areas of defoliation include Grantsville and along the ridgetop of Meadow Mountain in Garrett County, Green Ridge State Forest in Allegany County, and on the west side of South Mountain in Washington County.

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The defoliation is being caused by a native "looper complex" consisting of multiple species of geometer caterpillars. These caterpillars are also known as "loopers" or "inchworms" due to their unique way of moving; they make small loops with their bodies as they inch forward. The main species causing damage in Garrett County is the fall cankerworm (Alsophila pometari), while half wing geometer (Phigalia titea), linden looper (Erannis tilaria), and fall cankerworm are responsible for most of the damage in Allegany and Washington Counties. However, an invasive species called spongy moth caterpillar (Lymantria dispar dispar) is not contributing to this particular outbreak.

Despite the damage caused by these caterpillars, it is important to note that affected trees are not dead and will grow new leaves by late June or early July. However, repeated defoliation, especially in stressed trees on high ridgetops, can lead to tree mortality. The department's Forest Pest Management staff has observed natural predators of these caterpillars, such as birds, Calosoma beetles, parasitic wasps, and various diseases, which usually cause high populations to crash before significant tree mortality occurs.

For more information on looper caterpillars and other forest pests in Maryland, the public is encouraged to visit the Maryland Forest Pest Management website at mda.maryland.gov.

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