Public Works and Environmental Services

Fairfax County, Virginia

CONTACT INFORMATION: Our administrative offices are open to the public by appointment only at this time. Please call or email 8 a.m. – 4 p.m. Monday - Thursday; 9:15 a.m. - 4 p.m. Friday

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

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

Fall Cankerworm FAQs

What type of trees do fall cankerworms prefer?

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.

Have trees died from fall cankerworm?

Tree weakened by repeated defoliations may be more susceptible to secondary pests. It is difficult to determine how many trees in Fairfax County have died due to cankerworm. The Forest Pest Management Branch has been very successful in achieving the goal of preventing cankerworm defoliation and the resulting possible tree decline and mortality.

Why do fall cankerworms cause more damage to urban trees than to trees in a rural environment?

Fall cankerworm is a spring defoliator of hardwood trees.  Typically, trees defoliated early in the season will re-leaf by mid-summer and suffer only moderated growth loss.  Successive defoliations combined with other environmental stressors commonly found in an urban/suburban environment may lead to dieback and eventual death.

Fairfax Virtual Assistant