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.
- Watch the Fall Cankerworm Video!
- History and Background of the Fall Cankerworm Program
- Map of Fall Cankerworm Survey History in Fairfax County
- FAQs: Fall Cankerworm
What do I look for?
Severe infestations of cankerworms can cause widespread defoliation, tree stress and possible tree death. Major infestations and defoliation have occurred in Fairfax County. In the past, up to 5,000 acres have been defoliated by cankerworms.
2015 Supression Program Update
Urban foresters have detected high populations of cankerworms in portions of Mount Vernon and Mason Districts. To minimize tree mortality, the Fairfax County Forest Pest Management Branch has developed a 66-acre suppression program using hydraulic ground spraying equipment. In late April, Fairfax County will conduct spot treatment with the most environmentally sound insecticide available, Bacillus thuringensis kurstaki.
Fall Cankerworm Sticky Band Monitoring
Fairfax County Urban Foresters monitor the population of fall cankerworm insects each fall with sticky bands. These sticky bands are a band of tar paper wrapped and taped to a tree trunk and then covered in a very sticky glue. This technique takes advantage of the fact that female moths have no wings and must crawl up tree trunks where they get stuck in the Tanglefoot glue. Urban Foresters then count the number of female moths caught in the glue as a predictor of outbreak populations that would require further management.
We highly encourage residents to become actively involved in the fall cankerworm monitoring effort. If you are interested in cankerworm monitoring, click one of the links below. Sticky bands are installed starting in early to mid-Dec. and are removed approximately by the end of Jan. to coincide with emerging adult moths.
Homeowner Alternative Control Options
Fall cankerworms are a great source of food for wildlife, such as birds and beetles. Residents can create an inviting habitat for wildlife on their properties if they are looking for a natural control for fall cankerworms or other undesirable pests.
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 email.