The female Spongy Moth can lay between 600 to 1,000 eggs
Spongy Moth Scientific Classification
- Scientific Name
- Lymantria dispar
Spongy Moth Facts
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“Adult spongy moths only live for approximately two weeks!”
The spongy moth, formerly known as the gypsy moth, was one of the first completed projects of the Entomological Society of America’s Better Common Names Project. The name “gypsy moth” changed because it was derogatory to the Romani people.
In Canada and France, derived from the common name, “spongieuse” references the egg masses which appear sponge-like. The spongy moth is part of the Erebidae family and is divided into three subspecies. The species quickly spread once it was introduced to different continents. It is now in North America, South America, Asia, Africa, and Europe.
Their larvae survive on different coniferous and deciduous trees and often inflict significant destruction during seasons of mass reproduction. As a result, they are among the world’s 100 worst invasive alien species as compiled by the Global Invasive Species Database.
- Spongy moths are native to Asia, Japan, central and southern Asia, southern Europe, and northern Africa
- Adult spongy moths live for approximately two weeks only to reproduce
- Though they have wings, the European strain of the adult spongy moth cannot fly
- Female spongy moths will mate with only one male, while males are polygynous
- Spongy moths are incredibly destructive, feeding on the leaves of more than 500 species of shrubs and trees
The scientific name of the spongy moth is Lymantria dispar. Derived from Latin, the word Lymantria means “destroyer” and dispar means “to separate,” referring to the sexual dimorphism seen between the male and female during the last stage of metamorphosis.
Carl Linnaeus first detailed the spongy moth in 1758. Throughout the years, the classification has changed, which confused the taxonomy of the species. The family has moved between Erebida, Lymantriidae, and Noctuidae. In 1869, the species first appeared in North America. It became an invasive species once released from captivity. Various reports detail how and why this happened. Regardless, once released, various eradication programs began as the species quickly spread as far as the Pacific Northwest. The original intent was to breed the species with silk moths to create a silkworm industry in the United States.
Spongy Moth Appearance
Adult males and females have different appearances and coloration due to the sexual dimorphism which occurs in the last stage of metamorphosis, called the imaginal state. A few notable characteristics which distinguish the male and female are size, color, and antennae.
The adult female is more prominent, generally 30-35 millimeters long, compared to the adult male which is between 20-25 millimeters long. The female has yellowish-white wings with brown spots dotting the outside edges. Additionally, she has brown markings on the top of her forewings. In comparison, the male’s abdomen and wings are a brown and golden color. The male has dark brown markings on his forewings and brown stripes on his hindwings. The female has thin white antennae, while the male has long, feathery brown antennae. The male’s antennae capture the pheromone scents released by the females.
Spongy Moth Behavior
Food resources, predatory threats, and sexual competition affect the behavior from the larval, or caterpillar, stage to the adult moth stage. If the host tree provides suitable feeding the larvae will remain on the host for the remainder of its life cycle. However, if the host is not suitable, the larvae will use a process called ballooning. The larvae will climb up to the end of a shoot or branch and drop down a silk strand. They will hover in the air and wait for the wind to blow them to another host tree. The larvae can repeat this process until they find a satisfactory host. Most larvae will travel less than 200 yards from their hatch site, but studies have shown they can be carried up to half a mile by the wind.
The spongy moth will reside on the same host tree during their instar stages, the periods in which they will molt to grow. Males usually molt five times and females will molt six times, also known as six instars. During their early instar stages, the larvae feed during the morning and late afternoon, and by the fourth instar, they transition to nocturnal feeding. By dawn, they retreat to areas that provide the most protection, such as crevices and under bark or branches.
Upon emerging from their pupae state, males will fly searching out the pheromones emitted by the females who remain on their host tree to mate with them. While European spongy females do not fly, Asian spongy moth females do. The Asian spongy moth is capable of traveling long distances, which presents a real threat concerning the destruction of habitat. Female Asian spongy moths can lay their eggs on human-made objects, which allows the eggs to be easily transported. If they need new foliage to feed on, colonies can move from one place to another in pursuit of a new food source.
Spongy Moth Habitat
Spongy moths are a part of the Lepidoptera order which includes moths and butterflies. The species is non-native. It has naturalized and quickly spread. They reside in wooded areas and temperate forests whose density includes their primary host trees. In the United States, the species can be found throughout the northeast, including Minnesota, Tennessee and Maine.
Spongy Moth Diet
Spongy moths are herbivores and are voracious eaters while in their larva, or caterpillar, state. They consume foliage from more than 500 species of shrubs and trees. Most often densities of spongy moth are low and cause little noticeable damage. However, in years of high densities, the outbreak population can cause significant destruction by completely defoliating host trees. When outbreaks occur, they will often last one to five years. Factors such as prolonged defoliation and drought can result in crown dieback, reduced tree growth, and tree mortality. In North America, the preferred host trees of the spongy moth include alder, basswood, cherry, white birch, elm, maple, oak, trembling aspen, and willow.
Predators and Threats
Due to the invasive nature and frenzied breeding that occurs with spongy moths, there are not many threats to this species. The female has hair on her abdomen, which covers and protects the egg clusters. While birds such as the blue jay, northern oriole, robins, chickadees, and towhees will consume larvae, pupae, and adults, they are not a primary food source. However, the white-footed mouse and northern short-tailed shrew have proven important in regulating spongy moth populations, consuming larvae and pupae found closer to the ground.
Reproduction and Life Cycle
The spongy moth is a holometabolous insect, meaning it goes through a complete metamorphosis. The four stages of the life cycle are egg, larva or caterpillar, pupa, and adult. The eggs, which are found on tree branches or trunks, are laid in July and August close to where the female pupated. A female will mate only once, while males will mate multiple times. In her lifetime, the female will produce one egg mass, containing between 600 to 1,200 eggs.
The larvae develop in four to six weeks; however, the eggs enter diapause, a period of suspended development, to overwinter (approximately eight to nine months). In April or May, the egg will hatch and enter the larval, or caterpillar stage, which lasts about two months. The larvae are less than six millimeters when they emerge. During the summer months of May and June, the caterpillars are the most active and likely to cause destruction by defoliation.
In order to grow, the caterpillars complete several instar stages. They shed the exterior layer of their exoskeleton, before entering the next instar. In the first instar, the caterpillars are black. They present blue and red dots in their second or third instar. After completing her final instars, the female caterpillar is between 2.5 to 3 inches long, while the males are 1.5 to 2 inches long.
The larvae will seek out a protected area, which she will use to spin a cocoon and pupate. Cocoons are often found in tree bark crevices, under branches, or on outdoor items like planters and picnic tables. The pupation stage takes approximately two weeks, during which time the caterpillar completes its metamorphosis into an adult moth. Both male and female moths are sexually active upon emerging from their cocoons. The males typically emerge a few days before the females.
Adult moths do not eat, and they live up to two weeks exclusively for the purpose of reproduction. Mating occurs once per year typically in July or August. The female emits pheromones, a process known as “calling,” from a small gland near the end of her abdomen. The female can only mate once as she stops emitting pheromones after mating. The scent attracts males who fly in a zig-zag pattern in order to locate the female. Oviposition, or the depositing of eggs, occurs after mating and thus the cycle continues.
The population of the spongy moth is contingent upon factors such as food resources, weather, and predation. Outbreaks are cyclical and occur every 10-15 years. The population during this period varies, and if there are low numbers of predatory mammals and insects, the population can dramatically increase. If an outbreak occurs, it will typically last one to three years. Factors like disease, starvation, and predation will determine when lower populations emerge. However, the population often remains low and caterpillars and adult moths, along with their foliage consumption, go unnoticed.
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Spongy Moth FAQs (Frequently Asked Questions)
Why is the spongy moth a problem?
The spongy moth as a caterpillar has an insatiable appetite for over 300 varieties of shrubs and trees and poses a serious threat to North American forests. Losing foliage can leave the shrubs and trees vulnerable to disease and additional pests.
Can a spongy moth hurt you?
The hairs of the caterpillar can irritate skin, similar to poison ivy, but they are not harmful.
How do you get rid of spongy moths?
A bacterial insecticide spray called Bacillus Thuringiensis, also known as BT is the most common way to treat spongy moths. It is the preferred method, as it’s naturally found in soil, doesn’t affect other animals, and degrades when exposed to sunlight.
What causes spongy moth infestation?
One of the most common reasons a spongy moth infestation can occur is thought to be a drier than usual spring season. There is a fungus that is effective at keeping the population manageable. However, during a dry spring season this fungus is suppressed and unable to be as effective at killing off the caterpillars.
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- Wikipedia, Available here: https://en.wikipedia.org/wiki/Lymantria
- Portal.gov, Available here: https://portal.ct.gov/DEEP/Forestry/Forest-Protection/The-Spongy-Moth-Life-Cycle-and-Related-Moths
- CABI.org (1970) www.cabi.org/isc/datasheet/31807#totaxonomicTree
- CANR (1970) www.canr.msu.edu/resources/spongy-moth-life-cycle
- IUCN (1970) www.iucngisd.org/gisd/species.php?sc=96
- USANPN (1970) www.usanpn.org/data/forecasts/Spongy_moth