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Maryland Department of Agriculture

Spongy Moth Monitoring & Management

The spongy moth is by far the most destructive pest of forest and shade trees in Maryland. The caterpillars eat the leaves of oaks and other hardwoods in May and June. Heavy populations of caterpillars will eat most or all leaves in a tree. Large outbreaks have affected hundreds of thousands of acres statewide.

Although Maryland, like other states in the northeast, has suffered severe outbreaks of the spongy moth, the Maryland Department of Agriculture, Forest Pest Management Section has been highly successful in protecting our forest heritage.

Identification

The small caterpillars are mostly black with long hair. Older caterpillars have a light brown, mottled head and a dark-colored body with paired blue spots followed by paired red spots along the back.

The spongy moth caterpillar often is confused with the eastern tent caterpillar, which also appears each spring. Though very visible, the eastern tent caterpillar is not as serious a threat to trees.

Hosts

Spongy moth caterpillars are most commonly found on oaks, but feed on many different hardwood trees. Heavily defoliated trees may refoliate, but are still weakened, especially if defoliation occurs again the next year. Weakened trees are more vulnerable to other forest pests, diseases, drought, and other stresses, and may die. 

Biology

Eggs hatch in April. Young caterpillars feed in the tops of trees, while older caterpillars migrate up and down trees. Large areas of forests can be defoliated by heavy infestations.

Control

Removing egg masses and banding trees may help individual landscape trees; area-wide infestations may require large-scale insecticide treatments.​

The Forest Pest Management Section conducts an Integrated Pest Management (IPM) program for the spongy moth to minimize unnecessary losses as the result of the spongy moth, through monitoring, assessment, inform and education, and pest control. 

Since 1972, the Maryland Department of Agriculture (MDA) has conducted a variety of activities to help manage the spongy moth. MDA Forest Pest Management (FPM) personnel monitor the presence and severity of spongy moth infestations using different surveys. The types of surveys and where they are conducted have changed a little over the years, but the most important are surveys of spongy moth egg masses. Information from these surveys is used to assess the potential for damage and tree loss in each area and is provided to landowners, managers, and the general public.

Natural Controls & Monitoring

The spongy moth is attacked by predators, parasites, and, most importantly, diseases. These mortality agents are monitored by FPM workers. However, if these natural controls have not suppressed the populations, very high infestations may need to be treated with insecticide to protect trees in areas where dieback or mortality can't be tolerated.

Spraying for Spongy Moth

When such areas are threatened with defoliation, the Maryland Department of Agriculture, Forest Pest Management Section may propose aerial insecticide treatments to protect and preserve the forest and shade trees. Such treatments are conducted under the Maryland Cooperative Spongy Moth Suppression Program. The USDA Forest Service, Maryland Department of Agriculture, and local governments or landowners participate in this voluntary program.

See Spray Schedules and Maps

​More Information