Localized outbreaks of cankerworm occurred in southern Frederick and Washington counties this spring. The cankerworm is a native insect that becomes a moth at maturity. Cankerworms hatch from eggs laid on trees the previous fall. Cankerworms are of the family Lepidoptera.
This hatching occurs right around bud break in late April to early May and the larvae stay active until early June. Like most insects from the family Lepidoptera (butterflies, moths), it is the immature juvenile stage that does most of the feeding and damage to plants. After hatching, the young larvae begin feeding on leaves in a shot hole pattern. As the larvae enlarge they begin eating much of the soft leafy tissue, leaving on the leaf stem and veins intact.
This feeding activity can cause partial to complete defoliation of the tree.
Because this is a native insect, its numbers are normally held in check by natural predators such as birds and animals, so large outbreaks are uncommon. Normally large outbreaks only last for one or two seasons.
Cankerworms are also known as inchworms since they move in an accordion-like fashion, inching along as they crawl. Cankerworms can also be seen hanging from silken threads. By early June the cankerworm will drop off the tree, burrow into the ground and pupate. The adults emerge in the fall to mate and lay eggs before dying.
Cankerworms prefer elms, apple, oak, and hickory trees.
Normally a tree that is damaged by the cankerworm will refoliate soon after the insect is gone. These insects can impact orchards and weaken elm trees to the point that they are more susceptible to Dutch elm disease.
Article by FCFCDB member
Nature Note for 6/22/14