Spongy Moth (Lymantria Dispar Dispar or LDD moth)

Spongy Moth is a non-native invasive insect from Europe. During their caterpillar phase, Spongy Moth feed on the leaves of oak and other deciduous trees. Caterpillars chew small holes in leaves and can potentially decrease canopy leaf coverage. They are five to 60 millimetres long, dark and hairy with five pairs of blue dots and six pairs of red dots on the back.

In an effort to use more inclusive language, the City of Mississauga, as well as counterparts in Canada and the United States began phasing out the use of the common name “Gypsy Moth” in 2021. The preferred alternative is to refer to the species by “Spongy Moth,” or its scientific name, Lymantria dispar dispar (LDD for short).

The Spongy Moth was introduced to North America from Europe in 1869 in an attempt to develop a silkworm industry in the United States. In 1870, a small number of moths escaped, and, within 20 years, the Spongy Moth had become a serious pest. Despite a quarantine in place since the early 1900s in the United States, the Spongy Moth has been advancing slowly west-ward from the northeastern United States. The Spongy Moth was first detected in Ontario in 1969 on Wolfe Island, south of the City of Kingston.

Spongy Moth are known to feed on hardwood trees such as apple, ash, birch, cherry, elm, hickory, oak, willow and maple species. Other deciduous trees and even conifers such as pine or spruce could be susceptible when Spongy Moth populations are high.

High levels of Spongy Moth caterpillars can cause trees to experience a loss of leaves, which could lead to weakness and make them more susceptible to diseases or extreme weather events such as drought. Trees in urban settings may be increasingly susceptible to these impacts given the additional stresses they face including, soil compaction, restricted root volume, other pests, and human impacts.

Spongy Moth caterpillars tend to only feed on and damage trees for a short period in June and July. As the caterpillars grow, they consume more leaves. Later in this period, trees can look as if they have lost their leaves overnight.

Healthy trees are able to grow back their leaves within the season. However, several years of defoliation can weaken trees and have negative impacts on long-term health. Trees that are already stressed by other pests, diseases or extreme weather events, such as droughts, may also be disproportionately impacted.

Trees in Mississauga are essential to providing an array of social, environmental and ecological benefits to communities.

Trees help to:

• Improve air quality and reduce smog and pollution
• Provide shade
• Reduce energy demand for cooling in summer (shades buildings) and heat in winter (windbreak)
• Reduce the negative effects from urban heat (reducing the ‘heat island’ effect by shading paved surfaces and provides water vapour that cools the air)
• Prevent flooding and reduce peak storm water run-off volumes
• Increase property values and aesthetics and strengthens communities
• Improve emotional well-being and mental health (stress reduction)
• Increase outdoor activity and walkability, leading to improved health (e.g. cardiovascular)
• Provide habitat for birds and other wildlife in the city

Avoid exposure to Spongy Moth caterpillars. Children should be discouraged from playing with any Spongy Moth caterpillars. The spiny hairs on the caterpillars can cause welts or a patchy rash that can persist for four to five days. If you’re experiencing symptoms, contact a health-care professional.

The Spongy Moth is firmly established in Mississauga and across southern Ontario. Eradication is not feasible. Management programs in Ontario, Canada and the United States are based on minimizing impacts and slowing the spread of the invasive insect, but not eradication. Area containing host trees within the City of Mississauga will be periodically affected by the Spongy Moth for the foreseeable future.

The City’s Integrated Pest Management (IPM) program considers many options for Spongy Moth treatment: aerial spraying, ground spraying, individual tree injection, burlap banding and egg mass scraping. Each year, treatment options for Spongy Moth are determined following a robust monitoring program that is undertaken the previous winter by city staff and consultants. A number of factors are considered when determining treatment options to ensure that the significant resources required to treat trees and woodlands are expended only where there is a high likelihood of success and where the potential impacts on the tree/woodland health from not treating it are high. These factors include:

• Predicted risk of defoliation to a tree or woodland area
• Sensitivity of the tree or woodland area to the effects of defoliation (e.g.: size of tree, species of tree, and the number of years it has been predicted to have experienced defoliation).
• Current and predicted state of the Spongy Moth outbreak cycle
• Compounding stressors affecting a tree or woodland health, such as major storms or tree diseases
• Ability to access the tree/woodland for particular treatment types (for example, the height of the trees or the location of roads to allow for equipment access)

It is important to recognize that the Spongy Moth program is adaptive. Modifications to management criteria may occur to address situations where other stressors are present that may predispose trees to mortality or where particularly high value/specimen trees are present.

Egg mass removal involves scraping Spongy Moth egg masses from any surface where they are found. The eggs are placed in a bucket of soapy water for a minimum of 48 hours to kill the eggs before being disposed of. This activity can take place any time after eggs are laid, but typically occurs in the fall and winter months.

The City undertakes targeted Spongy Moth egg mass removal during the winter months. Egg mass removal is determined on a tree-by-tree basis, and is targeted to younger/smaller trees in high-risk areas so that staff are able to reach egg masses along the entire tree. Egg mass removal in large trees is not undertaken given the limited ability of staff to reach into the tree canopy rendering the activity ineffective for control.

Removing egg masses or caterpillars from private property is the responsibility of the property owner.

Burlap banding involves the wrapping of a particular tree with a band of burlap cloth forming a skirt. During the heat of the day, Spongy Moth caterpillars will crawl under the burlap seeking shade. Concentrated in this way, they can be easily picked off a tree and otherwise destroyed.

Installing burlap on trees is an effective, low-cost strategy that can be undertaken on a small scale by homeowners to reduce Spongy Moth populations on private trees, given that there is opportunity to check the burlap and destroy caterpillars on a regular basis.