Cankerworms aka inchworms. Spring and fall cankerworm images. Get inchworm facts and info about killing inchworms here. Controlling canker worm damage. Photo of inchworm or measuring worm larvae and moths.
The term "canker worm" is used, not to describe a single caterpillar, but a group of inchworms that cause damage to many different ornamental and fruit trees.
Two of the most common and most damaging of this group are the spring cankerworm, Paleacrita vernata depicted above and the fall cankerworm, Alsophila pometaria depicted below.
Like all caterpillars, inchworms have 3 pairs of legs at the front end of their bodies. They are distinguished from other worms by only having 2 or 3 pairs of legs at their rear ends. This causes their strange, looping gait.
The measuring worm "walks" by holding onto a branch with its forelegs and pulling its rear end forward. Then it holds on with the rear legs while advancing its front end. Each advance moves the canker worm about an inch forward.
P. vernata lays its eggs in the spring while A. pometaria lays its eggs in fall or winter. Both species hatch in the spring.
They only spend a few weeks in the larval stage before maturing into moths.
While in the larval stage, the worms feed on the leaves of oak, cherry, elm, apple, and maple trees (this is not an exhaustive list).
Measuring worm populations build up over a number of years and then die off naturally. In years where there are not many of them, the damage they do will be minimal and can safely be ignored.
When heavy populations are present, they can completely defoliate a tree in just a few weeks. This is when you need to step in.
Fortunately, killing inchworms is easy.
A simple spray of a Bt (Bacillus thuringiensis) will dispatch of the young cankerworms. Bt is a naturally occurring bacteria which interferes with the canker worm's ability to eat and causes it to starve to death.
Bt is safe to use around people and pets. Spray weekly until the munching stops.
Another way to keep these creeps off your trees is to apply Tanglefoot (sticky stuff) to the trunks in the spring. The worms get stuck in the band of Tanglefoot and can't climb into the tree's canopy to feed.
Both these controls are approved for use in organic gardening.
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