Lymantria dispar dispar (LDD)/ Spongy Moth

Lymantria dispar dispar (LDD), also known as Spongy Moth, is an invasive insect that has been found throughout Ontario. LDD/Spongy Moth is a defoliating insect that prefers to feed on the leaves of hardwood species causing the trees to lose some or in extreme cases, all their canopy. LDD/ Spongy Moth outbreaks are cyclical and generally surges every 7 to 10 years.  Favoured tree species include oak, birch, poplar, willow and maple. When their numbers are extremely high as they were in 2021, the caterpillar will feed on evergreens such as pine and spruce. Healthy trees can regrow their leaves during the same growing season. While most healthy trees can withstand several years of severe defoliation, trees that are already in poor health may have a harder time recovering which can result in tree morality. 

Current LDD/ Spongy Moth Stage

LDD/Spongy Moth are currently in the egg mass stage. Residents are encouraged to check their trees for egg masses and remove them. From now until the end of April/ early May residents can manually remove the egg masses by scrapping them into a bucket of soapy water. Leave the egg masses in the bucket for 2 days before disposing. Manual egg mass removal will help reduce the number of hatched caterpillars in the spring.

Residents are encouraged to wear gloves and long sleeves while removing pupae/cocoons and egg masses. For more information, please see the Management & Removal section below.

How to Identify LDD/ Spongy Moth

The LDD/ Spongy Moth has four distinct development stages similar to other butterflies and moths.The timing of each stage depends on climate and location.

cycle of the spongy moth

Eggs Mass: Late August - Early May

  • Tan-coloured and can be found on tree trunk and bark crevices as well as other hard surfaces such as outdoor furniture, decks and firewood piles.
  • The insect spends the winter in the egg stage, hatching the following spring.
  • One egg mass can contain 100-1,000 eggs.
  • Egg masses can be between 2-6cm in size
  • Spongy egg masses can be observed on the trunks and branches of infected trees.

Caterpillar: May - July

  • Greyish brown and hairy.
  • Caterpillars hatch from eggs in the spring (end of April/early May) and the emerging caterpillars climb up the tree to feed on the leaves.
  • During the early stage of growth, caterpillars are small and black.
  • Fully grown caterpillars have five pairs of blue dots and six pairs of red dots that run down its back.
  • Mature caterpillars can grow up to 6 centimetres in length.
  • Caterpillars can be found feeding on the leaves of trees causing defoliation and damage.
  • The caterpillar stage lasts approximately 40 days.

Cocoon/ Pupa: June - July

  • At the end of the caterpillar stage, the larvae seek shelter to pupate. In the early summer, larvae enter a transitional stage for 10-14 days in which the larvae transform into adult moths.
  • Once the adult emerges from the cocoon it leaves the empty cocoon behind which is often seen on infested trees.
  • Dark brown, shiny shell with hairs sticking out of the shell

Moth: July - August

  • The LDD/Spongy Moth has less than two weeks to mate and reproduce before they die.
  • Female moths can lay between 500 to 1000 eggs.
  • Male moths fly, female moths do not fly.
  • Female moths often remain on the tree they fed and pupated on.
  • Adult females are larger than males with white colouring.
  • Adult males are smaller and greyish- brown.