Spongy (LDD) Moths

The spongy moth is an invasive moth species from Europe that has established in southern Canada, as well as the eastern and central United States. It is a forest pest of concern because of the ability of the moth’s larvae (caterpillars) to defoliate trees (consume leaves). Healthy trees can typically survive severe defoliation by the spongy moth larvae; however, repeated defoliation stresses trees and makes them more vulnerable to other forests pests, diseases and drought.

Though the spongy moth accepts many tree species as its host, some of the more-preferred hosts include oak, maple, alder, beech, and birch species. Defoliation from larva feeding on leaves typically stops in early summer when the caterpillars have entered the pupae (cocoon) phase for one-to-two weeks.

Male and female adult moths then hatch from pupae around mid-July, but do not feed on the leaves of the trees. Instead, the adult moths spend their short-lived lives reproducing and laying egg masses to restart the life cycle.

Spongy moth population outbreaks occur in cycles, so while there may be an aggressive infestation one year, it does not mean it will continue year after year.

Learn more about the spongy moth’s life cycle and impacts:

• Toronto and Region Conservation Authority (TRCA)
• Credit Valley Conservation (CVC)
• Invasive Species Centre
• Ontario’s Invading Species Awareness Program
  

NOTE: Some of the resources may address the species as "LDD moth".

Like other Lepidopteran species (moth and butterfly species), the spongy moth has an egg, larval, pupal, and adult life stage.

Eggs are protected by a golden brown or yellow fuzz, in the form of an egg mass. One egg mass can host between 600 and 1000 spongy moth eggs. Egg masses stay dormant all winter and hatch the following spring during late April to mid-May.

Larvae (caterpillars) hatch from the egg mass and climb up to feed on the foliage (leaves) of the host tree. When larva hatch they are about 0.5 cm long and are very dark in colour. Over time (one to two months) the larva will continue to feed and grow up to 6-7 cm in length, and are identified by the five pairs of blue dots and six pairs of red dots along their backs.

CAUTION: spongy moth larvae contain hairs that can cause skin irritation or allergic reactions.

Pupae (cocoons) are formed by the larvae once they have matured (after about seven weeks of feeding). This one to two-week phase is how/when a larva transitions to an adult moth. When the adult moth emerges, the shell of the pupae is left behind. Female spongy moth pupae are often larger than the males, and are also larger than the males when in the adult stage. 

CAUTION: spongy moth pupae also contain hairs that can cause skin irritation or allergic reactions.

Adults (moths) are short-lived and seen in mid-summer. Both genders die after the (flightless) female lays a single egg mass on the limbs and/or trunk of the host trees. Egg masses can also be laid on surrounding rocks, buildings, or in other sheltered areas. Male moths are brown in colour, and females are white with dark markings (and larger in size). The moths do not feed on the host tree, they only reproduce.

Yes. Natural predators include parasitic wasps, beetles, and mice. When caterpillars first hatch, birds such as chickadees, blue jays, robins and nuthatches may prey on them. Young caterpillars contain fewer irritating hairs than adult caterpillars, making younger larva easier for animals to eat. Spongy moth populations are also reduced by diseases caused by fungi and viruses.

Depending on location and seasonal conditions, timing for managing infestation may overlap. These methods are also intended for individual trees and not large-scale woodlot management.

Inspect your property for egg masses between mid-August and the end of April of the following year. Conducting two search and removal efforts (one in the fall and one again in early spring) will ensure that all accessible egg masses will be found and destroyed. It is easiest to spot egg masses when the leaves are off the trees and shrubs.

Start in one corner of your property and walk in a systematic manner making sure to look high and low, on all types of vegetation and structures. Spongy moths lay their egg masses just about anywhere; but they prefer sheltered locations. Be sure to look at all natural and unnatural structures such as the underside of branches or bark, the underside of patio furniture, on stacks of firewood, rocks, and fences. Inspect all surfaces of your house including windowsill, under eaves, around bird houses or mailboxes as well.

LDD egg mass removal:

• Scrape egg masses off the tree (or other surface) into a water/soap mixture.
• Do not scrape egg masses onto the ground- they will still be able to hatch.
• Let the egg masses soak for a minimum of 48 hours. Stir the mixture occasionally to ensure complete coverage.
• Dispose of soaked egg masses into the garbage, and soapy water accordingly.

NOTE: Wear gloves when handling caterpillars and/or pupae since they contain hairs that can cause skin irritation or an allergic reaction.

The Town completed spongy moth monitoring by counting and assessing dormant egg masses attached to Town trees (located on the Town-owned section of streets and woodlot areas) throughout the municipality. Over 150 locations were monitored from January to March 2022.

The Town will use the monitoring data to predict the loss of leaves as well as what the 2022 outbreak population may look like. In general, monitoring has indicated that there is evidence of natural predators (birds, parasitic wasps) feeding on the egg masses. Overall, we have observed many masses which have not been intact or a “golden brown". This indicates they are not in a healthy condition or are egg masses from previous years.

Based on 2021/2021 egg mass monitoring data, 38 streets were selected for egg mass scraping efforts by the Town of Caledon’s Forestry Team. A total of 454 trees were scraped in the month of March based on monitoring efforts, and 15 locations were scraped based on service requests initiated by residents. 

Watch this video to meet our Invasive Species Coordinator and get an update on what the Town is doing to manage spongy moth throughout the municipality.

To help landowners manage spongy moth on private properties, the Town provided free burlap kits for pick up at various locations. Each kit contained two burlap bands, two pieces of twine and a burlap band how-to guide. 

Kits were made available in late April, and over 1000 kits were picked up by residents or handed out at various events hosted by the Town. 

Please note this service will not be provided in 2023.

Town of Caledon Forestry staff, and licensed exterminators working on behalf of the Town of Caledon sprayed trees with two rounds of Bacillus thuringiensis subspecies kurstaki (Btk). Btk is made from a naturally occurring bacterium found in soil and is the active ingredient in biological pesticides (biopesticides) approved for spongy moth management by Health Canada.

Btk was applied via ground spray application, using hydraulic sprayer equipment. For effective protection against spongy moth, a single tree required two Btk applications (about two weeks apart) to its leaves. When a spongy moth caterpillar consumes treated leaves, the Btk activates in the stomach of the caterpillar and kills it.

Only select trees that met specific size requirements and/or infestation levels were treated via ground spraying.

A second treatment option performed by licensed contractors was tree injections. Injections are conducted by drilling shallow holes into the trunk of a tree and placing canisters filled with a biopesticide inside the holes. Like water, the tree naturally uptakes the biopesticide and absorbs it into the tissues of the tree.

The pesticide used for tree injections is TreeAzin Systemic Insecticide®. It is also a biopesticide since its active ingredient is made from Neem tree (Azadiracta indica) seed extract. For effective treatment results, trees only require one injection treatment in a year. Overtime, the tree will heal and re-fill the holes within its trunk.  For more information on TreeAzin® visit the BioForest website.

Only select trees that met specific size requirements and/or infestation levels were injected throughout the municipality.

The Town installed sticky barrier bands on trees that met specific infestation levels but did not meet conditions suited for biopesticide application. Sticky barrier bands are most effective when caterpillars first hatch and are difficult to remove or hand-pick. The Town opted to use barrier bands that do not contain pesticides of any kind, and were removed in early July 2022. 

Prioritization of spongy moth management areas was dependent on the following:

• Infestation levels as indicated by winter egg mass monitoring
• Host tree species and height/size
• History of tree defoliation
• Proximity of infested trees to surrounding Town trees
• Current best management practices for spongy moth

• Installed early May, removed early July

Ground Spraying Treatments with Btk:

• Application period: May 24 - June 22  
• Two treatments were applied to trees approximately 7-10 days apart

Injections with TreeAzin®:

• Early June
• Only one treatment required
  
  

Please Note: Selected trees only received one biopesticide treatment type. A tree that was sprayed was not injected and vice versa. 

The Town of Caledon did not conduct an aerial spray in 2022. 

High counts of old egg masses from 2020/2021, signs of animals and parasitic insects feeding on egg masses, as well as cold winter temperatures supported signs of a declining outbreak population. These results were in line with observations made during the Ministry of Northern Development, Mines, Natural Resources and Forestry 2021 egg mass surveys, and observations made during monitoring conducted by local conservation authorities.

Impacts of outbreak population levels throughout the Town was predicted to vary between urban and natural forested areas. This is because trees experience different conditions, and pressures or stressors in these locations. The Town opted to manage highly infested urban areas (park and street trees) using methods such as sticky barrier bands, ground spray treatments with a Btk biopesticide, and injections with a biopesticide.

Aerial application of Btk biopesticide is not typically used in urban areas due to logistical limitations. Instead, aerial application is favoured for areas with remote or isolated woodlots. The Town of Caledon will continue to monitor Town-owned trees and will use the results to inform future management of the spongy moth. This could include aerial spraying Town-owned trees if it were deemed necessary and available as an option for the Town.