Public Works and Environmental Services

CONTACT INFORMATION: Our administrative offices are open 8 a.m. – 4 p.m. Mon - Fri - In-person meetings by appointment only.
703-324-1770 TTY 711
12055 Government Center Parkway
Suite 518, Fairfax, Va 22035
Brian Keightley
Division Director, Urban Forest Management

Fall Cankerworm

canker egg mass on tree limb
Egg Mass
Pennsylvania Department of
Conservation and Natural Resources
Forestry Archive

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 and enter the soil to emerge as adults in the fall.  You can look for the wingless females and their egg masses on the trunks of trees in January and February.

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

For further information, or if you find signs of this insect on your property, contact the Fairfax County Forest Pest Branch at 703-324-1770, TTY 711, or by email 

Recognize Fall Cankerworm and Signs of Infestation

Joseph Berger,
Female Adult Moth
Female Adult Moth
Photo by Matt Bertone, 2011
Male Adult Moth
Male Adult Moth
William M. Ciesla, Forest Health Management International,
Pennsylvania Department of Conservation and Natural Resources - Forestry Archive,
FAQs: Fall Cankerworm

Fall Cankerworm FAQs

Fall cankerworms feed on a wide range of hardwoods and favors maples, ash, oaks, hickories, beech and cherries. All of these are found in abundance throughout Fairfax County.

It is almost always a combination of stress factors over time that leads to tree decline and eventual tree mortality. Fall cankerworm is a spring defoliator of deciduous trees that is usually hardly noticed. In an outbreak however, when there may be 75%-100% defoliation, typically the trees will re-foliate by mid-summer. This decreases their energy reserves, leaving them more vulnerable to other stressors. The Forest Pest Management Branch recommends preventing successive (more than a single year) heavy defoliation that would contribute to tree decline and possible mortality.

Urban and suburban trees are under more environmental stress than rural trees. Improper planting, chemicals, construction, poor drainage, soil compaction, poor nutrition, lawn-care injuries, root damage, extreme temperature swings, changes in soil levels, excessive pruning, as well as an imbalance of natural organisms make urban trees less resilient. Trees that are defoliated early in the season will re-leaf by mid-summer and suffer moderate losses of energy reserves. Successive defoliations combined with other environmental stressors lead to dieback and eventual death.

Fairfax Virtual Assistant