Property Owner's Guide to Spongy Moth Management

The spongy moth is easy to recognize in all its stages. For pictures and additional information click on "spongy moth appearance", or go to the University of Maryland Home and Garden Information Center (HGIC) Fact Sheet listed on the right.

When you will see them: Usually the first sign of a spongy moth infestation is the appearance of large caterpillars in mid to late June. Sometimes, the homeowner will instead notice their droppings (called “frass”) on decks and walks around the home or other buildings. In the early spring, after the eggs have hatched, the tiny (about 1/8 inch) dark fuzzy larvae will be blown about in the wind and will be noticed if they land on your clothing or other light colored objects. Towards the end of June or in early July, the caterpillars will change into the pupal stage and in about a week the adult moths emerge, mate, and lay eggs, often in the same places the caterpillars and pupae were found (see “Where to find them”). Male moths are medium sized brown moths that fly during the day. They are not attracted to lights or flowers, but will be seen in early July fluttering around the trees and shrubs in the yard or woods. The female moth is larger, while with small dark markings and does not fly. She is found in the same locations as the caterpillars and pupae.

Where to find them: The larger caterpillars often crawl down out of the tree during the day and hide in or under objects in the yard or forest floor. Common places for them to be found are the undersides of branches, decks, rails, tables and so forth, underneath the leaves of climbing vines or ground cover plants, under leaves on the forest floor, behind signs, under roof overhangs, where siding of a building meets the foundation, and in the furrows and under flaps of bark on the trunks of larger trees.

What is a heavy infestation? Heavier infestations will produce a noticeable amount of frass, such that the walk or deck or pool needs to be swept or cleaned almost daily. If there are enough caterpillars, at night, the sound of their droppings will seem like a light rain. The landowner will notice holes or ragged edges to a lot of leaves, and the canopy will appear thin, with more light showing through than usual. Frequently, pieces of leaves drop to the ground in June as the large caterpillars eat through the middle of the leaf. Even if the infestation of caterpillars was not heavy enough to cause noticeable defoliation of the trees this year, there may be enough egg masses laid to cause a much greater problem the following year. Therefore, it is important to be able to recognize the gypsy moth egg mass (refer to the publication on the Home and Garden Information site). New egg masses can be seen any time beginning in August. They will typically be found in the same places where the large caterpillars (and the pupal stage) were found. Ten or more egg masses per oak tree on your property is cause for concern!

There are two important reasons to talk to your neighbors about gypsy moth infestations on your properties. First, is so that you each can be informed about any infestation. Your neighbor needs to be aware of any infestation you have since it can spread to near by properties the following spring, and likewise you will learn of any infestation your neighbor(s) may have - and which may be even heavier than yours! Second, any control actions you taken will be more effective and less expensive if you and your neighbors work together, especially if you chose to hire an applicator. Also, it is best to review with your neighbor any options for control you are considering.

The feasibility and effectiveness of the various options will depend on the size and severity of the infestation in your area (see #2 above).

The time to take action is well before your leaves start disappearing! It is best to aim control actions can be aimed at the egg masses or the young caterpillars. Large numbers of egg masses are commonly found in wood piles and on man made objects in the yard. The firewood should be burned, and egg masses can be scraped off lower parts of the trees and house and off objects in the yard any time before early-mid April when they begin to hatch. However simply scraping the eggs on to the ground will not necessarily kill them, so they should be collected and disposed of in the trash, or buried. There are few products registered to spray on egg masses, and unfortunately, the most effective ones are not generally available.

There are a variety of over the counter insecticides that can be used against the caterpillars, but all will be more effective if used when the caterpillars are still small but feeding which is usually during the first couple of weeks in May. The insecticides are applied to the leaves. Contact your local Cooperative Extension agent or go to the Home and Garden web site or call 800-342-2507 for control recommendations. However, it should be kept in mind that heavier or larger infestations may not be controlled adequately by home-owner methods, and a licensed pesticide application firm may need to be contacted. Click on “Commercial Applicators” for a current list of licensed application firms offering gypsy moth control services in your county.