SPONGY MOTH
(Lymantria dispar)

Name and Family

Spongy Moth, Lymantria dispar, is a member of the Erebidae family.

History

Identification Guide

  • Spongy moth overwinters in the egg stage.
  • Eggs appear in masses, and are coated with a soft, spongy-looking substance.
  • In the spring, eggs hatch and the gypsy moth larvae move up the tree and feed on the newly emerged leaves.
  • They mainly feed at night so often you will see the damage to the leaves of your tree but not the larvae.
  • Young caterpillars produce silken threads that catch in the wind and blow them to neighboring trees.
  • More mature larvae begin to feed day and night and can very quickly defoliate your tree.
  • You can identify the larvae by the 5 pairs of blue spots and 6 pairs of reddish spots on their back.
  • Once the larvae are mature (usually around July) they find a protected place such as a crevice in the tree bark, form a cocoon and pupate.
  • Adults emerge in late summer.
  • The males are brown, are strong fliers, and have feathery antennae.
  • Females are white, flightless, and have simple antennae.
  • The adults do not feed and only live for about a week… just long enough to mate and lay eggs.

What it does in the ecosystem

  • Spongy moth is a voracious generalist feeder of over 300 tree species. 
  • It poses a significant risk to forest health, and can spread quickly. 
  • Outbreaks have been known to defoliate entire forests, decreasing tree health and increasing susceptibility to damage and disease. 
  • Fortunately, the pest is considered “cyclical” meaning that large reproductive events only occur every 7-10 years.
    • Most mature trees can survive defoliation at this rate. 
  • Under 20% of trees will die from spongy moth defoliation, but that figure is still significant. 
  • Besides defoliating trees, caterpillars can also cause skin irritation in humans. 
  • An additional revolting result of spongy moth infestation is that in times of mass reproduction, frass (poop) can literally rain down from the trees. 

Management

GENERAL CONSIDERATIONS

  • Spongy moth management is an involved process, but eradication is feasible for new moth outbreaks. 
  • Several effective and ecologically friendly control methods exist. 
  • If you believe you have a spongy moth infestation on your property, begin by ensuring that you have correctly identified the insect.
    • The moth has some native lookalikes that do not require control. 
  • Before selecting a control method, consider the size of the infestation, your available resources, and the amount of effort you are willing to expend.
    • Often, multiple control methods are used simultaneously. 
    • You must also consider the local ecosystem and what other organisms or ecological processes may be affected by management.

PHYSICAL CONTROL

  • Spongy moth egg masses can be scraped off the surfaces of trees and outdoor equipment using a scraper.
    • Scrape the masses off and place them into a bucket of hot soapy water or burn them. 
    • This practice is labour-intensive. 
    • All egg masses may not be easily accessible to scrape away. 
    • Scraping will in any case reduce the number of eggs in the ecosystem and thus the number of larvae that hatch to defoliate the trees. 
    • Scraping should take place from August to May, as this is when the most egg masses will be present. 
  • Physical removal of caterpillars is feasible and can be simplified by using a burlap banding technique.
    • Wrap an infested tree in burlap at chest height and tie a rope around the burlap about two-thirds of the way up. 
    • Let the upper portion of the burlap drape down over the lower portion.
      • This will create a little pocket held up by the rope. 
    • During the day, caterpillars will seek refuge in the burlap pocket. 
    • Visit the trap daily and remove and kill all caterpillars by placing them into hot soapy water. 
    • Wear gloves, as some people will experience skin irritation or an allergic reaction when handling the caterpillars. 
    • Wrapping the tree in bands of sticky material can trap and kill caterpillars without much labour input. 
    • These methods are effective from May to July when the caterpillars are present.


CULTURAL CONTROL

  • An indirect way to control spongy moth is to increase the number of natural predators found in the area. Blue Jays, robins, chickadees, mice, squirrels, and ants have been found to prey upon the various spongy moth life stages. 
  • Place feeders, plant native plants, and install birdhouses to attract these types of visitors!

BIOCONTROL

  • Biological control agents have been widely tested for this species. 
  • A spray infused with the bacteria Bacillus thuringensis kurstaki (Btk) is available.
    • The bacteria only affects insects in the Lepidoptera (butterfly) family, making it safe for other ecosystem inhabitants. 
    • Once ingested, the bacteria will release a toxin, killing the caterpillar. 
    • Btk should be applied to affected foliage twice between May and June when the caterpillars are most active. 
  • Other biological controls include specific viruses, fungi, and insect parasites. 

CHEMICAL CONTROL

  • A professionally administered insecticide called TreeAzin has been proven effective in controlling spongy moth development. 
  • Unfortunately, this treatment is costly and not specific to spongy moth.
    • Other insects that feed on the tree will be killed as well. 
  • For these reasons, this method is not readily recommended.
  • Mating disruption has been shown to be an effective means of reducing spongy moth numbers.
    • Pellets containing the sex pheromone that attracts males to the flightless females are released aerially. 
    • The male moth will become attracted to the pellets, ignoring the female moth. 
    • Other insects in the area will be unaffected by the treatment as the pheromone is specific to the spongy moth. 

POST-TREATMENT

  • Continue to monitor the outbreak year after year to repeat control measures as needed. 
  • Spongy moth may be found elsewhere in your area and may return to your property from elsewhere even if your eradication was an initial success.
  • Diligence is key to the control of this invasive pest. Your trees will thank you for it!

Map

Click to open map in a new tab.

Male moth antennae are generally quite feathery. They use their antennae for “smelling” things like the pheromone from a female gypsy moth.
The female spongy moth is much larger than the male and, unlike the male, it is flightless. This means it lays its eggs very close to where it pupated… mostly on branches and tree trunks but could be on anything nearby like firewood, campers, bikes, boats… things we move around and inadvertently move the gypsy moth with us!
The male spongy moth is brownish in color, smaller than the female and is a strong flier.
The spongy moth larva be identified by the 5 pairs of blue spots followed by 6 pairs of reddish spots that are on its back. This can vary some, but blue dots followed by red dots is a good indication you have found a gypsy moth larva.
Female spongy moth lay eggs in the fall which then, overwinter. The egg masses are covered with fine hairs from the females abdomen. These hairs protect the eggs from predators, insulate them in cold temperatures and help to keep the eggs dry. Mild winters contribute to the eggs successfully overwintering.

References

Spongy moth (Lymantria dispar dispar) – Canadian Food Inspection Agency (canada.ca)

Spongy Moth – Profile and Resource | Invasive Species Centre

Spongy Moth | National Invasive Species Information Center

Spongy Moth – Canadian Council on Invasive Species (canadainvasives.ca)

Spongy Moths and Controlling Populations – Hamilton Conservation Authority (conservationhamilton.ca)