Fall cankerworm larva

Fall cankerworm female moth laying eggs

The fall cankerworm, Alsophila pometaria, is a native defoliating insect found throughout much of North America. The caterpillar stage of these insects is often referred to as inchworms or loopers. Fall cankerworms feed on a wide variety of trees but tend to prefer maples, hickories, ashes, and oaks, all of which are found in abundance throughout Fairfax County. Fall cankerworm caterpillars emerge in early spring and feed on leaves for about a month. Once the caterpillars mature, they drop off the trees, enter the soil, and pupate. You can look for the wingless females and their egg masses on the trunks of trees in January and February.

Infestations in Fairfax County

Severe infestations of cankerworms can cause widespread defoliation, tree stress and possible tree death. Major infestations and defoliation have occurred in Fairfax County:

• 1996 and 1997, along the George Washington Parkway near Mount Vernon
• 1998, nearly 1500 acres of defoliation throughout the Lee and Mount Vernon Districts
• 1999, nearly 5000 acres of defoliation in southeastern Fairfax County
• 2002, approximately 2000 acres of defoliation in the Mason Neck area of the county

Since 2002, no significant defoliation has been detected in the county. County foresters will continue to monitor fall cankerworm populations and develop suppression programs as warranted.

For further information, or if you find signs of this insect on your property, contact the Fairfax County Forest Pest Branch at 703-324-5304, TTY 711, or via e-mail.