Spongy moth: declared pest

Page last updated: Tuesday, 4 October 2022 - 1:34pm

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The larval stage of Spongy moth (Lymantria dispar) is a severe defoliator of a wide range of broadleaved trees and shrubs. This pest is not present in Western Australia. Its early detection and reporting will improve chances of eradication and containment to help protect native plants, forests, and tree plantations in WA.

What plants are affected?

  • More than 1000 plant species including eucalypts, pine trees, fruit, and nut trees.

What do I look for?

  • Egg-masses are tan to rust coloured or very pale, with a fine felt-like appearance. These may contain 400-1000 eggs.
  • The moths lay egg masses on hard surfaces, usually tree trunks and branches but also on logs, outdoor furniture, nursery stock, pallets, shipping containers and on the hulls and rigging of ships.
  • Caterpillars are pale to dark grey and hairy (up to 7cm long). They present two rows of raised spots on their back – five pairs of blue spots followed by six pairs of red spots. Occasionally they may have all-blue spots. Caterpillars below 2 centimetres may lack the coloured spots.
  • Caterpillars feed in groups, defoliating trees. Young caterpillars are extremely voracious resulting in branches and sections of a tree suddenly losing their leaves.
  • Male moths are grey-brown (3-4 cm wingspan) and female moths are pale yellow with wavy dark brown bands (4-7 cm wingspan).
spongy moth caterpillars have distinctive blue and red spots along their body
Caterpillars have distinctive blue and red spots along their body
female moths lay masses of eggs with a spongy appearance
Female moths lay egg masses with a spongy rust coloured appearance
spongy moth caterpillars defoliating tree
Caterpillars can quickly devour foliage
caterpillar infestations can result in defoliation of entire tree plantations
Caterpillar infestations can result in defoliation of entire tree plantations 

How does the pest survive and spread?

  • Spongy moth larvae overwinter as eggs. Although it only takes about one month for larvae to develop inside of the eggs, they usually do not hatch for 8 or 9 months.
  • Masses of eggs are located closer to the ground or within crevices which protect them from cold temperatures. Eggs can resist temperatures up to −20°C without freezing.
  • Mature larvae pupate within a silk nest on a trunk, rock or in leaf litter until complete development within three weeks to emerge as moths.
  • Spongy moth larvae can feed on many hosts, making it a very adaptable invasive species. Feeding patterns depend on larval stages (instars):
    • Eggs usually hatch in spring, coinciding with the budding of most hardwood trees.
    • Feeding activity in the first three instars only occurs during daylight hours, but from the fourth instar onwards feeding occurs at night.
    • Young larvae travel from the bark of the tree to feed on the new foliage by cutting small holes in the surface of leaves. Food intake increases as the larvae grow and feed on the edge of the leaves.
  • Young larval stages can travel up to 200m by spinning silk from their head and travelling on wind currents. They can travel several kilometres and reach new hosts when departing from an elevated position.
  • Spread over long distances occurs through human activity such as the movement of infested plant parts, wood, nursery stock, machinery, and equipment as well as on cargo. Shipping containers are considered a major contributor to the spread of the pest worldwide.

What damage can this pest cause?

  • Caterpillars can defoliate trees in farms, orchards, bushland, plantations, and sometimes whole forests, causing billions of dollars damage. Spongy moth is considered the world’s third most costly insect.
  • In high numbers, larvae can strip all leaves from a tree. Severe defoliation can reduce tree growth and predispose trees to attack from other insects and diseases.
  • Spongy moths hold great potential for damage to commercial radiata pine plantations, impacting in building and furniture industries in Western Australia.

Status in Western Australia

Lymantria dispar is absent from Western Australia and is a quarantine pest. It is a prohibited organism under section 12 of the Biosecurity and Agriculture Management Act 2007.

Western Australia's Pest Freedom for spongy moth is supported by general and specific surveillance and specific import requirements to prevent its entry.  A person who finds or suspects the presence of spongy moth in bushland, natural reserves, plantations, nurseries or urban areas must report it to DPIRD.

What do I do if I find it?

It is important that any suspect spongy moth occurrence is reported. Early detection and eradication will help protect Western Australia’s fruit production and nursery industries, and the environment. If you find or suspect plants with spongy moth, please make a report using MyPestGuide® Reporter or contact the Pest and Disease Information Service (PaDIS) to report this pest.

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Pest and Disease Information Service
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Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080
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