Fall cankerworm is an eastern-US native caterpillar that episodically defoliates hardwood forests. This particular spring 2024 outbreak southeast of Pittsburgh was particularly extensive. The largest region seeing this outbreak was on Laurel Hill, including portions of Forbes State Forest.

Eggs hatch in April or early May, and defoliate trees as leaves emerge in spring. Fall cankerworm's preferred host trees include hickory, maple, ash, beech, basswood cherry and oaks, which are common in southwestern Pennsylvania's forests. At landscape scale, variation in preferred host prevalence and caterpillar population density interact to create the observed variation in severity that these 10m HiForm maps document.  Like defoliation from the non-native spongy moth, defoliation generally occurs with strong local variation in severity with core areas that are largely denuded of canopy foliage to areas where perhaps half the leaf area has been lost.  

According to reports, this 2024 defoliation may have been the most severe since 1977.