Spongy Moth (LDD Moth)

Same insect; new name: The Entomological Society of Canada (ESC) has adopted the new common name of 'Spongy moth' for Lymantria dispar dispar (LDD) moth. The Township, among many other government, agencies is adopting this new name.

The Spongy moth is a non–native insect pest that has become endemic to much of Southern and Central Ontario, with outbreaks occurring every seven to ten years. The invasive Spongy moth in Ontario is beyond the stage where it can be eradicated and as a result is expected to continue to have periodic population increases with varying levels of defoliation. In Ontario, major outbreaks have peaked in 1985, 1991, 2002, and 2008. Additionally, there was an upsurge in Simcoe County beginning in 2019, with moderate to severe levels of defoliation in 2020 and 2021.

Spongy moth outbreaks are not uniform throughout municipalities, forests, and woodlots each year. The population level in specific areas depends on several factors, including forest composition (tree species), weather conditions and topography / landscape features. Spongy moth populations vary annually and fluctuate with local conditions.

Despite the successful use of insect predators, as well as fungal and viral controls, Spongy moth populations do occasionally reach outbreak levels and continue to expand their range. Spongy moth caterpillars defoliate host trees, mostly hardwood species such as oak, birch, poplar, willow, maple and others. During peak outbreak years, broadleaf trees may be completely defoliated, caterpillars appear everywhere, and 'frass' (caterpillar droppings) appear to rain from the trees.

As experienced in 2020 and 2021, Spongy moth outbreaks are triggered by warm winters and hot, dry spring and summer months. However, a series of natural factors can cause a Spongy moth population collapse. These include cold winter temperatures (below -20°C), heightened tree defenses (i.e., development of tougher leaves from regrowth and less nutrients), competition for food, predation, parasitism, and naturally occurring diseases—NPV (nucleopolyhedrosis virus) and an introduced fungus (entomophaga maimaiga).

NPV is one of the most important factors in the collapse of Spongy moth outbreaks in North America. NPV spreads naturally when caterpillars are abundant, regardless of weather conditions. Its presence has been detected in Simcoe County Forests and within the Township. In turn, the fungal disease is dependent on cool wet weather to facilitate the spread of fungal spores. Both naturally occurring diseases result in mass mortality of Spongy moth larvae, supporting the known cyclical nature of Spongy moth outbreaks.

The Spongy moth has four distinct developmental (life cycle) stages like other butterflies and moths:

Egg Mass - typically seen September through April
Caterpillar - typically seen May through June
Pupa - typically seen July through August
Adult Moth - typically seen July through August

Property owners are encouraged to monitor trees on their property and take action by removing Spongy moth where possible. Look for egg masses in the winter and spring, caterpillars in the spring, and moths in July through August.

Residents may pick up a Burlap Banding Kit from the Township to assist with removing Spongy moth from trees on their property. In the event that managing populations becomes unfeasible through the methods described, seek a professional tree care company for assistance. Tree care professionals can provide options for tree injections and ground spray methods.

Residents are also encouraged to Report an Spongy Moth Infestation through the Township's online reporting tool. This tool will help inform and coordinate monitoring efforts across the Township.

TreeAzin Injections

For larger trees, it is recommended that you consult with a private arborist about the possibility for pesticide injections. Injections work for larger trees that can’t be sprayed from the ground, or are too difficult to access. TreeAzin is a commonly used botanical injectable pesticide formulated with an extract of neem tree seeds. It provides a treated tree with protection from Spongy moth feeding for one season. When a caterpillar eats the leaves of a treated tree, the pesticide kills the insect by preventing it from growing any larger. This limits the amount of damage to the tree. High-risk trees—trees that are predicted to be severely defoliated—are generally selected for this treatment. The timing of treatments is essential for successful control.

Spray Programs

Property owners may also consider a commercial spray program to help control spongy moth populations while preserving the trees on their property. Insecticides or biological controls such as BTK (bacillus thuringiensis kurstaki) may be used to help control spongy moth population on private property. Before considering the use of BTK, consult with a Certified Arborist or Professional Forester to apply sprays or tree injections. These insecticides are most effective during the caterpillar stage, therefore, the timing of the application and treatment of the entire canopy is essential to the success of control. While these applications may not completely eradicate Spongy moth populations, they can be effective in reducing Spongy moth population when used appropriately.

To contact a Certified Arborist or Professional Forester, please visit:

International Society of Arboriculture​

Ontario Profes​​​s​ional Foresters Association​

The Township will continue to monitor Spongy moth while working with the County of Simcoe and Severn Sound Environmental Association (SSEA) and other nearby municipalities on best practices to control populations.

The Township is currently providing 150 Burlap Banding Kits for residents to control Spongy moth populations on their property. Kits can be picked up at three locations while supplies last:

• Township Administration Centre - 2231 Nursery Road Minesing, ON L9X 1A8
• Springwater Library (Elmvale Branch) - 50 Queen St W, Elmvale, ON L0L 1P0
• Springwater Library (Midhurst Branch) - 12 Finlay Mill Rd, Midhurst, ON L0L 1X0

It is recommended that burlap wraps are installed in mid-May or whenever you start to see caterpillars crawling on your tree. Spongy moths will move down the tree trunk to seek shelter from the heat and predators. By installing a burlap trap, it will make it easier for you to collect Spongy caterpillars and help reduce the amount of Spongy moth on your tree. It is recommended to leave the traps up from June to August and to check the burlap skirts daily while picking off the caterpillars with gloves. The caterpillars should be placed into a container of soapy water and should be left in the soapy water for 24-48 hours. Afterwards, dispose of the water accordingly.

Below is a simple 4-step process that will allow you to install a burlap trap on your tree:

Spongy moths are most destructive during their larval stage, as caterpillars strip away tree foliage by consuming leaves. In most cases, trees will be able to regrow their leaves. Certain species (such as oak trees) are more vulnerable and the preferred food of Spongy moth caterpillars. These species require intervention as repeated defoliation can weaken a tree's defense system causing long-term, negative impacts to the tree.

The Township will not be spraying Spongy moth with pesticides in 2022. The use of pesticides has a limited time window to be effective, and requires weather conditions and lifecycle of the Spongy moth caterpillars to be favorable. As such, the effectiveness of pesticides is limited.

Additionally, spray pesticides not only kill Spongy moth caterpillars but other species of caterpillars as well, which can have a negative impact on native species of moths and butterflies.

At this stage of the infestation, the Township is not undertaking an aerial spray program. Township staff will continue to work with the County of Simcoe to monitor egg masses and defoliation to estimate insect populations. Based on reported data and in consultation with experts and partners in Ontario, Township staff are developing future response plans for Spongy moth outbreaks.

The hairs of spongy moth caterpillars contain histamine which some people can be allergic to. While not everyone will have a reaction if they come in contact with a Spongy moth caterpillar, it is possible to have an adverse effect.

If you experience any sort of reaction to Spongy moth, please contact your family care physician for medical advice.

There is a wide variety of insects, birds and small mammals that eat Spongy moth eggs, caterpillars, pupae and adult moths. There are more than 40 predatory bird species in Canada that are known to feed on Spongy moth. Some of the best known are the blue jay, American robin, black-capped chickadee and gray catbird. Tiger beetles, stinkbugs, ants, the yellowjacket, and the bald-faced hornet are some of the better-known insects that help maintain low residual Spongy moth populations between outbreaks. Among small mammals, shrews, moles and mice are effective predators. There are also more than 100 insect parasites that attack Spongy moth at the egg, larval and pupal stages.

There are also two other natural controls that cause Spongy moth populations to collapse, including Nuclear Polyhedrosis Virus (NPV) and Entomopgaha maimaiga fungus. Combined, these two natural controls will infect healthy egg masses, which are typically the size of a toonie. Where NPV and fungal infections occur, egg masses will reduce to roughly the size of a dime. This is a good indication that the Spongy moth population is unhealthy, leading to a mass die off.