The spongy moth (Lymantria dispar dispar) is a non-native insect from France. In New York, spongy moth caterpillars are known to feed on the leaves of a large variety of trees such as oak, maple, apple, crabapple, hickory, basswood, aspen, willow, birch, pine, spruce, hemlock, and more. Oak is their preferred species. Spongy moths have "naturalized" in our forest communities and so they will always be around.
- spongy moth factsheet (PDF)
Spongy moth has several life stages:
- Egg masses are light brown in color and appear as fuzzy or spongy patches on tree trunks, branches, firewood, or in a sheltered spot, even on lawn furniture. Each egg mass contains 600-700 eggs.
- As a newly hatched caterpillars, they are tiny, black, and eat tender new leaves.
- Caterpillars grow to about 2.5 inches in length and have five pairs of raised blue spots followed by six pairs of raised red spots along its back. The hairs on their backs can cause mild to moderate skin irritation in some people.
- Female moths are white with brown markings and cannot fly. Males are brownish and are often seen flying around in summer and fall.
Tent caterpillars look similar to spongy moths and also feed in the spring. However, unlike spongy moth, tent caterpillars are native species and are an important food source for a number of bird and other wildlife species.
|Forest Tent (Native)
|Eastern Tent (Native)
|Dark compact cylindrical mass with square ends, encircling the branch. New masses are shiny without holes. Old masses are dull and show exit holes. Deposited around small twigs in July. Masses may contain up to 350 eggs, average 150 in NY.
|Dark compact cylindrical mass with tapered ends encircling the branch. New masses are shiny without holes. Old masses are dull and show exit holes. Deposited around small twigs in July. Masses contain up to 350 eggs.
|Tan-colored or lighter fuzzy patches (masses) on tree trunks, branches, firewood, or in a sheltered spot, even on lawn furniture. Usually 600-700 eggs/mass.
(Ansel Oommen, Bugwood.org)
|Larvae (caterpillar) appearance
|Dark with light blue lines down sides and line of white "footprints" down back. Light blue heads. Fully grown is about 2 inches long.
|Dark with white line down back with light blue and black spots on sides. Black head. Fully grown is about 2 - 2 ½ inches long.
|Five pairs of raised blue spots followed by six pairs of raised red spots along back. Fully grown is about 2 inches long.
(Whitney Cranshaw, Colorado State University, http://www.forestryimages.org/)
(Lacy L. Hyche, Auburn University, http://www.forestryimages.org/)
Minnesota Department of Natural Resources Archives, http://www.forestryimages.org/)
|Hatch at bud break in spring. Tend to migrate to treetops. Feed on opening buds and new foliage one branch at a time. Young larvae are gregarious, often group together, follow each other in a line, and form silken mats on trunk, branch or leaves where they gather, rest and molt. Older larvae are nomadic foragers even prior to complete defoliation.
|Hatch at bud break in spring. Congregate in obvious silken tents in branch forks. Feed on opening buds and new foliage in colonies. Use tent to rest and as protection from extreme temperatures, rain, birds and other predators. Larvae leave the tent to feed. Fully grown larvae leave the host tree to find a protected place to pupate.
|Hatch when oak buds are opening. Younger larvae chew small holes in the leaves. Older larvae feed from the outer edge of the leaf toward the center. Will feed until tree is stripped, then go in search of food. When feeding will leave behind noticeable frass (droppings). When populations are sparse, larvae feed at night, crawling down the trunk to hide in a protected spot during the day. When populations are dense, feeding occurs day and night. When tree is stripped, larvae go in search of new food sources.
|Solitary cocoons, pale yellow silk in folded leaves or protected areas
|Solitary cocoons, white silk with yellow powder
|Hard brown case, pointed at one end in sheltered location
|Light brown with two narrow dark bands/stripes on the forewings. Lay eggs on hosts. Strongly attracted to light. Sexes look similar.
|Reddish brown with two white stripes on forewings. Sexes look similar.
|Females do not fly. Females are white with brown markings. Males are brownish.
|Most common host trees
|Sugar maple, aspen, cherry, apple, oaks, birch, ash, alder, elm, basswood and willow. Does not feed on red maple, sycamore or conifers
|Mostly cherry, apple, and crabapples, also other fruit trees ash, birch, maple, oak, poplar, and occasionally pecan, hawthorne, beech and willow
|Oaks preferred. Also apple, sweetgum, speckled alder, basswood, gray and white birch, poplar, willow and others. Avoid ash, yellowpoplar, sycamore, black walnut, catalpa, locust, American holly, and shrubs such as mountain laurel, rhododendron and arborvitae. Older larvae will also feed on conifers such as hemlock, pines, spruces and southern white cedar. When populations are dense, larvae will feed on almost any tree and shrub.
Spongy moth populations rise and fall in cycles of roughly 10-15 years.
- Populations vary during the cycle, from years with few caterpillars and very minor damage, to years with large numbers of caterpillars and very noticeable leaf damage and tree defoliation.
- Population cycles are driven by predator-prey interactions and a decrease of predators can cause high populations, or outbreaks, of spongy moth.
- Outbreaks occur every 10-15 years in New York State.
- Outbreaks are usually ended by natural causes such as disease and predators.
Distribution and Habitat
Spongy moths were accidentally introduced in 1869 when they were brought to the U.S. in the hope that they could breed with silkworms to create a hardier variety of silkworm and develop a silk industry in the US. Even though they failed as a textile producer, some of the spongy moths escaped and established their first U.S. population in Medford, Massachusetts.
According the U.S. Forest Service, the current "invasion front" stretches from North Carolina across to Minnesota and includes: Maine, New Hampshire, Vermont, New York, Massachusetts, Rhode Island, Connecticut, Pennsylvania, Delaware, Maryland, Michigan, Wisconsin, Minnesota, Illinois, Indiana, Ohio, West Virginia, Virginia, and North Carolina.
Although thousands of acres of trees can be damaged, spongy moths do not pose a major threat to New York's forests overall. Deciduous trees (trees that lose their leaves each fall) can regrow a new set of leaves by July and can usually withstand 2-3 successive years of defoliation (removal of leaves) without being killed. However, spongy moth can impact the health of individual trees.
- Defoliation reduces a tree's overall health and resistance, making it more susceptible to pests and diseases.
- Tree death can occur when other stresses such as disease or other insect outbreaks attack trees in the same year.
- When populations are very high, or when oak and other preferred trees are limited, spongy moth will eat evergreen species including pine, spruce, and hemlock. Evergreens do not regrow leaves as easily as deciduous trees and can die as a result of complete defoliation.
How to Control Spongy Moths
Please note that all of these options may protect individual trees or small areas, but they will not erase a local spongy moth population now or in future years. In large forested areas, manual removal is often not practical during an outbreak.
DEC and its partners typically do not manage spongy moth, and treatments are usually limited to ecologically or culturally significant forests. At this time, DEC does not provide funding for controlling spongy moths on private property.
Caterpillars are always being naturally controlled by birds, rodents, parasites, and diseases. Extremes in temperature can also reduce population numbers.
Squishing and Scraping
When populations are low or when you have just a few trees you want to protect, spongy moth caterpillars and adults can be killed by squishing them. Egg masses can be destroyed by scraping them off trees or other structures and dropping them in a container of detergent.
Bands, Barriers, and Traps
In late April, sticky/barrier bands may be placed around the tree's trunk to catch caterpillars when they hatch and crawl. These bands can be bought or made at home using common household materials. View detailed instructions on how to make and use your own trap on the University of Wisconsin website. If you choose to use a barrier band, please check it often in case unintended wildlife pass through, and replace as necessary after rain events.
In mid-June when caterpillars are larger, replace sticky/barrier bands with a burlap trap. View detailed instructions on how to do this on the University of Wisconsin website.
When considering whether to act or not, consider the extent, severity, and context of the outbreak first, as most management options generally can not impact regional spongy moth outbreaks. In certain cases it may be economically feasible to spray large areas. For example, maple syrup producers may be interested in aerial spraying since severe defoliations can reduce maple syrup production. If you are considering spraying, start planning in fall or winter as many of these services book up early. Various insecticides for spongy moths are available at garden centers.
Microbial insecticides are biopesticides made from naturally occurring bacteria, viruses, fungi, or protozoans that can be targeted to a specific pest. The most common of these is Bacillus thuringiensis (Bt), which occurs naturally in soil and on plants. The Bt subspecies kurstaki (Btk) is the most appropriate to use for LDD control.
Btk works best on young caterpillars, which become more resistant to treatment as they mature. When Btk is eaten, the caterpillar becomes paralyzed, stops feeding, and dies of starvation. Btk is harmless to people, animals, and plants, but does affect other young moth and butterfly larvae. Proper application will help limit exposure to non-LDD larvae.
Chemical insecticides are contact poisons. These chemicals can have an impact on a variety of beneficial, native insects (such as bees), as well as nesting birds and other wildlife so they should be used wisely. Spraying is not effective against spongy moth pupae or egg masses, and it is less effective once caterpillars reach 1 inch long.
Horticultural oil insecticides (aka dormant oils) are solutions refined from petroleum or plants and, when applied, smother insects or disrupt the protective coating around eggs. As with chemical insecticides, horticultural oils are non-selective but have the advantage of being relatively safe for humans and animals. The oils should be applied to egg masses in late March to early April before caterpillars emerge, and again in October to early November after adults have ceased activity.
Greater detail on insecticide treatment and timing can be found in the US Forest Service's guide to spongy moths. Professional pesticide applicators can be found online. In order to use restricted insecticides, applicators must be certified. You can check the certification status of a pesticide applicator on our website. We also recommend reviewing our tips for selecting a tree service.
You can use the egg sampling survey (PDF) in winter to determine if you will have a large infestation and may want to consider spraying.
How to Help Trees Recover From Defoliation
Most healthy trees can withstand a couple years of leaf loss from spongy moth caterpillars. Long-term damage depends on the type of tree as well as how much defoliation took place:
- Conifers - If a needle-bearing tree loses more than 50% of its needles, it probably won't recover. Check it for new needle growth in the months after the caterpillars are gone.
- Hardwoods - A healthy leaf-bearing tree will likely leaf out again as the caterpillars disappear in July/August, though leaves will probably be smaller than usual. If a tree loses ALL its leaves and does not grow any new ones in late summer, check it in the spring. If it still does not leaf out next spring, it has died.
If you have concerns about a dead or dying tree, or if think your tree could endanger a house if it were to fall, contact an arborist .
Losing lots of leaves in spring or summer can stress and weaken trees, which makes them vulnerable to pests, diseases, or competition from invasive plants that move into the now-sunny understory. If you have trees that show signs of recovery after the caterpillars have gone, check on them in the following months to watch for potential issues.
Urban or suburban trees that have been impacted by spongy moth caterpillar damage can benefit from some extra care such as:
- watering during dry or drought conditions,
- weeding around the trunk,
- mulching properly - just 1-2 inches deep and away from the trunk - IF you plan to mulch, and
- scraping off spongy moth egg masses in fall/winter (if applicable).
If you are a woodland owner who saw multiples acres impacted by the caterpillars, watch for new leaves in mid to late summer. If you are considering spraying, start planning in fall or winter as many of these services book up early.