Another Snack: Forest Tent Caterpillar Returns for Sixth Year of Defoliation

By on June 17, 2020

The forest tent caterpillar is the larva of a golden-brown moth. While the adult form is plain, the caterpillar has a splash of bluish lines running along its sides with a row of white dots on top. Many describe the shape of these white dots as keyholes, footprints, or, cutest of all, little penguins.
Image: Steven Katovich, Bugwood.org

The year 2020 is bringing plenty of surprises, but another forest tent caterpillar defoliation is not one of them. For the sixth year in a row, the forest tent caterpillar is causing damage along the Roanoke and Chowan Rivers and near Lake Waccamaw in the coastal plains of NC. However, with a global pandemic and social distancing guidelines in place, figuring out the extent of this damage looks a little different in 2020.

Normally, N.C. Forest Service surveyors take to the sky to determine the extent of the outbreak. This year, aerial surveys were not possible due to COVID-19 social distancing guidelines. Surveyors are normally next to others in a small airplane cabin for hours at a time while completing aerial surveys, so to maintain safe distance, information was gathered differently this year. Using past defoliation data, remote sensing (using data received via satellite technology), and field reports from N.C. Forest Service personnel, surveyors documented this year’s defoliated areas without a formal aerial survey. Based on this, an estimated 59,300 acres near Lake Waccamaw and another 99,400 acres along the Roanoke and Chowan Rivers were impacted. While it is not the ideal mode of assessing the damage, remote sensing proved a valuable alternative for estimating the location and size of the defoliation when traditional surveying is restricted.

Due to social distancing guidelines, surveyors turned to remote sensing to map the areas of defoliation near Lake Waccamaw (left) and along the Roanoke and Chowan Rivers (Right). Nearly 159,000 acres are estimated to have been defoliated by the forest tent caterpillar in NC in 2020. Map: K. Oten, NCFS.

Forest tent caterpillars are considered cyclical pests, which means outbreaks occur and subside regularly. Historically, outbreaks normally last three to six years. Hopefully, this sixth event is our final year of defoliation!

The forest tent caterpillar boasts a beautiful design, but it can cause extensive defoliation, or loss of leaves. The caterpillars snack on leaves of bottomland hardwood trees like oaks, gums, maples, and tupelos. They can eat most or all the leaves off a group of these trees during an outbreak. Despite what their name implies, these caterpillars do not spin tents. Instead, they create silken mats on the trunk of trees where they congregate to rest or molt.

The forest tent caterpillar defoliates hardwood trees, as shown in this image captured during a forest fire patrol flight near Lake Waccamaw. Image: Bobby Parker, NCFS.

Extensive defoliation from the forest tent caterpillar can lead to stunting and dieback in trees, but most of our trees recover without long-term damage due to the long growing season in North Carolina.  The caterpillars are usually controlled by natural enemies, such as parasites, predators, and diseases. On individual trees, they can also be controlled by simply removing the caterpillars and their mat from the tree.

Many areas affected by the defoliator are already starting to recover. Based on historical events, we may not see a seventh year of forest tent caterpillar defoliation. Only time will tell if these hungry caterpillars decide to make a reappearance!

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