How to identify and get rid of cankerworms

Picture this: you’re admiring the lush greenery of your backyard when you notice something’s not quite right. Leaves are chewed up, and some trees look like they’re barely hanging on. You might just be dealing with cankerworms, a common foe for trees during the spring or fall.

These little caterpillars can cause quite a headache for any homeowner who prides themselves on their garden. Cankerworms, also known as inchworms, are the iconic caterpillar we see in media today. They fold themselves up to then stretch and inch their way along a branch or leaf.

There are two species of concern in North America: the fall and spring cankerworm. If their numbers are high enough, they can easily defoliate young trees, including elm, apple, oak, maple, hackberry, ash, and many more tree species.

Cankerworms go through a cycle of high populations for 2-7 years, followed by a population crash for 13-18 years. This can make it seem like the population has exploded overnight. However, because of Dutch elm disease, there are fewer elm trees in urban and rural settings, and that has prevented too many outbreaks over the years.

Cankerworms are easily recognized by their inchworm-like movement, where they loop their bodies as they crawl, earning them the nickname “inchworms.” These pests are about an inch long and can be green or brown, allowing them to camouflage seamlessly with the foliage they feed on.

Spring cankerworms will have two pairs of “fake” legs or prolegs near the end of their body, while fall cankerworms will have three.

Signs of an infestation include noticeable chewing damage on the edges of leaves, leading to defoliation in severe cases. During heavy infestations, these caterpillars might also dangle from trees on silk threads, especially in the spring. They are similar in color to a beet armyworm with the greenish color.

How big are cankerworms?

Cankerworms can grow up to 1 inch long.

They can be found throughout the United States, especially in deciduous forests. They are rarely found inside homes but can be on urban trees.

Cankerworms can be difficult to eliminate in a forest setting, but they are manageable for trees in your yard. Fully mature trees can suffer damage for up to three years before they start to weaken. However, younger trees may be more susceptible.

Here are a few ways you can prevent cankerworms from taking over:

• Band trees: Wrap sticky bands around the trunks in early spring to catch females climbing to lay eggs.
• Remove egg masses: Scrape off egg masses from tree bark during winter.
• Encourage natural predators: Birds, beetles, and spiders are natural predators of cankerworms.
• Prune affected limbs: This can help reduce the population on individual trees.
• Try a solution like Pestie to keep them out of your home!