Spongy Moth Suppression

The Macomb County Spongy Moth Suppression Program (formerly known as the Gypsy Moth Suppression Program) was established in 1993 and is administered by Michigan State University (MSU) Extension. The program is provided to residents in both rural and urban areas within the county.

Why is there a Spongy Moth Suppression Program?

The Spongy Moth is a foreign pest with few native predators to keep populations in check here in the United States. It was introduced to Massachusetts in 1869 and has spread across the much of the northeast. Spongy Moth outbreaks began to occur in the lower peninsula of Michigan in the mid-1980’s. Caterpillars feed on tree leaves, preferring those of oak, aspen, poplar, and birch but will feed on over 500 types plants throughout the summer. Large populations can defoliate entire wooded areas. Caterpillars in large numbers (and their waste, frass) are a nuisance in residential areas. Spongy Moths cannot be eradicated, but they can be suppressed to tolerable levels.

What are the goals of this program?

Reduce high caterpillar populations to tolerable levels
Reduce tree loss by preserving at least 60% tree foliage, to reduce stress on trees
Prevent indiscriminate use of chemical controls
Provide educational information

How are Spongy Moth populations suppressed?

The main defense is an aerial application of Bacillus thuringiensis var. kurstaki (Btk), used to reduce high populations of Spongy Moth caterpillars at sites that meet certain guidelines for treatment. Btk is a naturally occurring bacterium found in the soil and is not harmful to pets, birds, fish, plants, beneficial insects, or humans. Btk specifically targets only caterpillars of a certain age. It is applied when the caterpillars are young (usually in May) to ensure the greatest impact in reducing numbers. Alternative mechanical techniques, such as tree banding, egg mass scraping, and hormone traps to help reduce populations. The suppression program recommends the use of a combination of methods.

What is the Spongy Moth life cycle?

The Spongy Moth life cycle has four main stages: egg, caterpillar, pupae, and moth.

Egg stage

In mid-August, after mating with the male moths, the females lay their eggs in masses. Egg masses are generally firm, oval shaped, about the size of a quarter, and buff or tan colored. Egg masses are laid on any surface, such as tree bark, rocks, woodpiles, decks, buildings, and outdoor equipment. Since Spongy Moth complete only one life cycle per year, eggs laid in mid-August do not hatch until spring.

Spongy Moth (Lymantria dispar) egg mass starting to hatch with many small caterpillars emerging.

Photo credit: USDA Forest Service, USDA Forest Service, Bugwood.org

Caterpillar

The eggs hatch into caterpillars late April or early May. Hatch date is directly affected by weather. The colder the spring, the later the eggs hatch. A healthy egg mass can hold 1000 eggs, although the average is probably between 300 and 500. Once the eggs hatch, the caterpillars will remain on the egg mass for a few days before they leave to feed. In its short lifetime, a caterpillar can eat one square meter of leaves. Mature caterpillars are about 2” in length with long hairs grouped in bundles. They have 5 pairs of blue dots and 6 pairs of red dots running down their backs. Their heads are black with yellow markings.

A Spongy Moth caterpillar.

Photo credit: Daniel Herms, The Ohio State University, Bugwood.org

Pupae

In mid-July to mid-August, mature caterpillars stop feeding and weave silk around their bodies to form a hard, brown shell or cocoon. In this pupa stage, caterpillars start their metamorphosis or change into the moth stage of the life cycle. This process takes about two weeks.

Three Spongy Moth egg masses on the trunk of a tree with a pupae casing (left).

Photo credit: Daniel Herms, The Ohio State University, Bugwood.org

Moths

Moths, the adult stage of the life cycle, emerge from the pupal cases in mid-August. The moths do not eat and they live only for a week. Female moths have white wings with brown chevron or ‘V-shaped’ markings and do not fly. Male moths have smaller brown wings and are able to fly. Attracted to a pheromone emitted by the female, the males can fertilize several females before dying. Female moths lay egg masses that remain dormant until spring.

Adult female (right) on an egg mass with an adult male (left).

Photo credit: Daniel Herms, The Ohio State University, Bugwood.org

How do Spongy Moths travel?

Caterpillars hang in trees on a silk strand and can be carried a great distance by the wind. Humans also move egg masses or pupal cases on travel trailers, firewood, cars, etc. Vehicular travel is how they came to Macomb County! Make sure you do not give the Spongy Moth a ride.

How do I know if I have Spongy Moths?

A number of MSU Extension bulletins can help you identify the Spongy Moth and caterpillar. You can also use the Macomb County MSU Extension diagnostic facility. There is a small fee for some services.

What does Spongy Moth damage look like?

Spongy Moth caterpillars feed on tree leaves creating ‘swiss cheese’ type holes. They do not cause pre-mature leaf drop, browning, or curling of leaves. They do not make a web or tent in trees. In addition to damage to the trees, Spongy Moth caterpillars can be a nuisance if populations are high enough. Caterpillars and their frass (feces) can drop down from trees on to sidewalks, driveways, yards, porches, and vehicles. Frass can stain surfaces, especially if it is rained on or becomes wet. Additionally, the hairs on the caterpillars can cause irritation or an allergic reaction to bare skin.

What happens when trees are defoliated?

Trees defoliated more than 40% become stressed by using next year’s energy reserves to grow new leaves during the same season. Healthy trees may withstand several years of defoliation. Evergreens are unable to replace their needles and may die when defoliated. Keep trees watered and fertilized to reduce any stress.

Should I report a Spongy Moth infestation?

Yes! To determine if your property is eligible for the Spongy Moth Suppression Program, report all infestations to the program coordinator at the Macomb County MSU Extension office. An egg mass survey can be done to assess the level of infestation and determine if an area qualifies for the program. For more information, please contact:

Macomb MSU Extension Spongy Moth Suppression Program (586) 469-6432.