What are these small green worms in my trees? 

The small green worms you find in your trees are called cankerworms or inchworms. Cankerworms overwinter as eggs in the top of shade trees and typically hatch at the end of March and early April.  

What do inchworms look like?  

Cankerworms can be green, brown or brown with a black stripe. They are called inchworms because of the peculiar movement they do.  

Are inchworms harmful to plants? 

Large enough populations will defoliate a tree, however, since the feeding happens in early spring most trees will push out new buds and leaves to full recover from cankerworms. Four to five weeks after hatching, the cankerworm will drop to the soil to pupate which means that they are only harmful to trees for a short period of time.  

How to control inchworms? 

Since the wingless females must crawl into the trees to lay their eggs, attempts at control are often made during this time by banding surrounding trees with sticky material. Another control method is to introduce a bacterial pathogen called Bacillus thurigiensis (Bt.) to the early instar cankerworms, about 10 days after hatch. This spore forming bacteria causes a fatal disease in cankerworm, but timing is critical with this method as it is not effective on the latter instar cankerworms. 

The surest control is to spray your high value, susceptible trees with a residual contact insecticide. The application should coincide with the larvae emergence and the tree’s leaves should be expanded considerably. This chemical application will not eradicate the cankerworm but will offer some protection to the tree from defoliation. An arborist can advise of the need to treat the trees or not, before applying pesticides.  

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