Just as trees begin to leaf out in the spring season, spongy moth caterpillars (formerly gypsy moth) are hard at work, eating those brand-new leaves.

As spongy moths strip trees of their leaves, trees become weak and susceptible to other injuries.

When it comes to tree pests, the best thing we can do is learn more, then take proactive steps to control them. Here are all the gypsy moth facts you need!

Spongy Moth Caterpillar: The Damage It Does and How to Control It

Where did the spongy moth come from?

Originally from Europe and Asia, spongy moths made their debut in the U.S. more than a century ago. In the late 1860s, Leopold Trouvelot transported a trove of moths to his Boston home.

Soon after, the first spongy moth outbreak was around 1890.

How many spongy moths are expected in Massachusetts?

As the birthplace of the U.S. spongy moth outbreak, Massachusetts trees are especially affected by the insects.

The good news is that the moths are slowing down this year. The University of Massachusetts reported that nearly 90 percent of spongy moths died last year. The rain in 2017 activated a native soil fungus that reduces the spongy moth population.

But that doesn’t mean spongy moths are gone for good. Defoliation is expected in Essex, Hampden, Hampshire, Norfolk, and Worcester Counties. But, Massachusetts trees won't experience the extreme rate of leaf loss they have in past years.

What's the life cycle of the spongy moth?

Spongy moths go through four stages.

  1. Adult moths lay eggs toward the end of summer.
  2. The following spring, usually around late April or early May, young caterpillars emerge. That’s when they begin feeding on all your new tree leaves!
  3. After eating your trees for about a month, the caterpillars rest in their pupal cases.
  4. Sometime during July or August, they emerge as white or brown-winged moths. They get ready to lay eggs, which starts the whole process over!

What kind of damage does the spongy moth do?

Spongy moth caterpillars partially or entirely strip trees of their leaves. They prefer oaks, especially white and chestnut. But they’ll also eat alder, aspen, basswood, birch, hawthorn and willow trees.

Then, because the tree is weak from the loss of its leaves, it becomes vulnerable to other problems.

Like people, when trees get weak, they’re more susceptible to certain pests and diseases. The year of the drought, we lost a lot of trees or they were under stress," said the manager of Hartney Greymont, a Davey company.

How can I control the spongy moth?

The best advice? Be proactive. Here’s what to do:

  • If you have damaged, compromised, or beloved trees in your landscape, be prepared to treat those trees early if spongy moth injury is expected. Talk to your arborist about applying a well-timed insecticide treatment. An ounce of prevention goes much further than no prevention at all.
  • Consider adding a tree band in late May. These trap spongy moth caterpillars as they hike up and down your tree.
  • Fertilize your tree to improve its ability to recover from spongy moth damage.
  • Water your tree on dry days in the summer to prevent any added stress from drought.

Ready to rid your tree of a spongy moth infestation? Talk to your arborist about a plan.


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