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Spongy moths (Lymantria dispar): Identification and control strategies

Theme: Pest guides

Overview:  

Spongy moths, previously called gypsy moths, are a species of moth native to Europe and are therefore considered invasive in North America. They are also referred to by their scientific name Lymantria dispar. The larvae of spongy moths (sometimes referred to as gypsy caterpillar moths) are responsible for the damage caused by these pests. The larvae feed on the leaves of a large variety of trees leading to defoliation (leaf loss) which can cause the plant to die after repeat infestations. 

In this article, we will provide an overview of spongy moths, including how to identify them and how to get rid of them using biological approaches. 

What are spongy moths?

Spongy moths are an invasive species of moth that are considered significant pests in the United States and Canada. Spongy moth caterpillars feed on the leaves of many types of trees, both leafy and evergreen, and can significantly damage plant health over time. ​​When the caterpillars are young, they can be brown or black and are about 0.6 cm long. Mature caterpillars can be 6-7 cm long and are easier to identify with their dark colour and a double row of 5 blue spots on their back followed by a double row of six red spots. Adult male moths are light brown and fly, while females are larger, white, and flightless. 

Females lay their eggs on trees which overwinter in this form. Eggs hatch in late spring and the caterpillars create silk threads which allows them to be carried to other host plants by the wind. The caterpillars feed on leaves for several weeks before developing into adult moths. Adults are short-lived and the females die after laying their eggs. 

A close-up image of a Gypsy Spongy moth caterpillar showing red two red spots on the lower half of the spine feeding on the leaf of an unidentified plant.
Spongy moth (formerly gypsy moth) Lymantria dispar. Credit: USDA Forest Service, Bugwood.org

What are the different types of spongy moths?

There are three primary subspecies of the spongy moth: the European, Asian, and Japanese spongy moth

Spongy moths/european (Lymantria dispar dispar)

This moth is a major forest pest in Canada, where it inflicts significant damage on deciduous forests. The European spongy moth can cause canopy loss, which weakens trees over time and makes them less resilient to environmental stresses. The damage this pest does can cause significant economic damage as well as loss of habitat for other animals. 

Images of Spongy moth adult. An adult female (upper) showing the mainly light colours with brown markings and male (lower) showing mostly brown in colour with dark brown patterning.
Spongy moth (formerly gypsy moth) adult female (upper) and adult male (lower) (Lymantria dispar (Linnaeus, 1758)) – Credits: USDA APHIS PPQ, USDA APHIS PPQ, Bugwood.org 

Asian spongy moth (Lymantria dispar asiatica)

This pest is known to attack hundreds of plant species and cause significant economic damage. Female Asian spongy moths are capable of flight which means that this subspecies has a greater capacity for spreading compared to the European variety. It is commonly found in Russia, China, Korea, and Japan, though there are reported incidents of it spreading to North America.

A full-length image of an Asian spongy moth (Lymantria dispar asiatica) larva, observed on the side of a tree.
A larva of the Asian spongy moth (Lymantria dispar asiatica) – Credits: John Ghent, Bugwood.org 

Japanese spongy moth (Lymantria dispar japonica)

As the name suggests, this moth is native to Japan, though it has also become established in Russia. Like the Asian spongy moth, females of this subspecies can fly, increasing their ability to travel to new areas. This species is considered a significant pest and can feed on a huge variety of plant species.

A male adult Japanese spongy moth brown in colour with small darker markings (Lymantria dispar japonica)
Japanese spongy moth (Lymantria japonica) – Credits: DAFF Archive, Bugwood.org 

What is the impact of spongy moths?

Spongy moth caterpillars (larvae) cause damage by feeding directly on the leaves of plants. This can lead to significant loss of leaves which impacts the plant’s health. In addition to many species of trees, spongy moths can attack shrubs and fruit plants. Typical fruit plants attacked by spongy moths include apples, pears, cherries, and peaches. Orchards in areas with high spongy moth populations can experience a significant loss of yield due to the impact of this pest. 

Are spongy moths dangerous to humans?

Adult spongy moths are not considered dangerous to humans. However, the small hairs present on spongy moth caterpillars can cause itching and rashes when they come into direct contact with the skin and respiratory issues when inhaled, particularly in sensitive individuals. 

How do I know if I have a spongy moth problem?

Spongy moth egg masses remain visible on trees throughout winter making them a clear way to spot this pest. These masses contain 100-1000 eggs and are light brown or tan-coloured. The larger the size of the egg mass the greater the local infestation. During feeding, caterpillars can be easily identified by the distinctive blue and red spots as described above

A close-up shot the 'spongy' egg mass from a Spongy moth, attached to a tree.
Egg mass of spongy moth populations (formerly gypsy moth) (Lymantria dispar) – Credits: Milan Zubrik, Forest Research Institute – Slovakia, Bugwood.org 

How do I get rid of spongy moths?

Though these pests pose a significant threat to many industries and habitats, integrated pest management (or IPM) strategies can offer solutions to control spongy moth populations. As preventative measures, we encourage individuals in high-risk areas to regularly check their vehicles or equipment for egg masses. If you spot an egg mass, you can scrape it off with a knife and discard it safely. 

Biological control

Biological control involves using products with a biological source. This includes microbials, natural substances, semiochemicals, and macrobials. 

Microbials

These are microorganisms such as bacteria, fungi or viruses that kill pests. The nucleopolyhedrovirus virus kills spongy moth larvae around 10 days after infection. Gypchek is a product containing this virus and should be applied as a spray when spongy moths are in their early larval stage. Many products use a bacteria called Bacillus thuringiensis which also kills many pests in their larval stage. This bacteria is usually applied in a spray. 

Natural substances

These are products derived from nature that kill pests. Azadirachtin is found in neem seeds and has potent activity against spongy moth larvae. Treeazin systemic insecticide is a product containing azadirachtin. It is injected directly into the base of the tree and can provide two years of protection with a single dose.

A farmer observing a bottle of Neemazal. an insecticide containing neem oil
Example of an insecticide: Neemazal azadirachtin. Credit: CABI

Semiochemicals

These are a group of organic compounds, such as pheromones, that organisms use to communicate with each other. Econex Lymantria dispar disperses male spongy moth pheromone, significantly disrupting spongy moth mating. Since adults are short-lived, products like these need to be used at specific times during the spongy moth lifecycle.

Macrobials

These are insects which naturally kill pests. The greenhouse rove beetle is predatory in its larval and mature state and is a natural predator of spongy moths. Parasitic wasps that deposit their eggs within spongy moth eggs are also useful for controlling pest numbers. Species used for this purpose belong to the genus Trichogramma.

Conclusion and future directions

The spongymoth is a critical environmental and economic challenge in North America, particularly in Canada. Canadian authorities, along with the United States Department of Agriculture, the Washington State Department of Agriculture, and various other states’ departments of agriculture, are actively implementing strategies to curb its spread. These efforts are supported by insights from the Entomological Society of America, which contributes vital research and guidance on effective pest control techniques. 

Biological strategies offer a solution to spongy moth infestations without causing damage like chemical pesticides. These strategies include the use of microbes, semiochemicals, natural substances, and releasing natural native predators (macrobials). Integrated pest management strategies are important for maintaining the health of forests and orchards and preventing economic damage caused by spongy moths. 

To discover more about biological control, you can visit our article which explores this topic in more detail. For specific solutions to spongy moths, please visit the CABI bioprotection portal.

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