Caterpillars Count: Invasive Spongy Moths in Southern Ontario
Invasive Spongy Moth (Lymantria dispar dispar) caterpillars are a common species found during EcoSpark’s Caterpillars Count surveys. Should you spot a Spongy Moth caterpillar or one of their egg masses, report your observations to EDDMapS or contact Ontario’s Invading Species Hotline. In this blog you will learn more about this species, its population control, and what can be done to slow its spread.
Caterpillars Count is a citizen science project that studies arthropods to understand their population abundance and seasonal changes (their phenology). Data on arthropod populations is helpful to understand food availability for forest and migrating insectivorous birds. Identified by their black hairs, and pairs of red and blue bumps, Spongy Moth caterpillars were one of the many arthropods found in our Toronto ravine survey site at Brookbanks park.
Native to Europe and Asia, the moths were first located in Ontario in 1969 where they later destroyed the leaves of native trees. The leaves of softwood and hardwood trees, oak especially, are defoliated by the moths’ large appetite. This can cause stress to the trees and leave them more vulnerable to diseases and insects. Most of the damage occurs when the moth is in the caterpillar stage. From its hatching in the spring to July, the caterpillars eat numerous leaves as they mature. Large periodic population bursts of the caterpillars can strip trees of their leaves on a massive scale if not controlled.
Spongy Moth populations are naturally limited by predators, parasitoids, and pathogens. Birds, small mammals, ants, and beetles are predators that feed on the Spongy Moth. Parasitoids are organisms that need a host to survive and kill the host as they grow. Specialized wasps and flies are parasitoids of the Spongy Moth, laying their eggs in or on the caterpillars. Finally, a fungal disease (Entomophaga maimaiga) and the NPV (nucleopolyhedrovirus) viral disease are two pathogens that cause Spongy Moth death.
Despite natural population control, widespread damage still occurs. Many Ontario municipalities have programs to prevent harm to urban forests. The City of Toronto has four methods of Spongy Moth removal used throughout various neighbourhoods. Treatments include manual egg removal, tree injections, ground sprays, and aerial sprays. Wondering what they inject/spray on the trees? Injections are usually a form of pesticide which is incorporated into the leaves and kills the caterpillars if eaten. Sprays contain BTK which is a bacterium from soil that does not harm other organisms. The spray laces the leaves and protects them from caterpillar damage.
So, what can you do to keep the Spongy Moth population under control? Unfortunately, they have become well established in Ontario forests and cannot be eliminated entirely. But they can be stopped from spreading further. As mentioned above, you can report your sightings to EDDMapS or the Ontario’s Invading Species Hotline. You can also participate in Caterpillars Count with EcoSpark to gather data on these creatures. If you like getting messy firsthand, look for their spongy egg masses on tree trunks, vehicles, outdoor furniture, and other flat surfaces. They can be scraped off and killed in a container of soapy water. Caterpillars can also be removed by hand and squished – but be careful of a possible allergic reaction to their hairs.
Happy exploring!
References
City of Toronto. (2020). European Gypsy Moth. Retrieved from https://www.toronto.ca/services-payments/water-environment/trees/forest-management/threats-to-trees-insects/european-gypsy-moth/
Government of Ontario. (2020). Gypsy Moth. Retrieved from https://www.ontario.ca/page/gypsy-moth
Michigan State University Extension. (1999). Natural Enemies of Gypsy Moth: The GoodGuys! Retrieved from https://www.canr.msu.edu/uploads/files/e2700.pdf
Ontario's Invading Species Awareness Program. (2012). Gypsy Moth. Retrieved from http://www.invadingspecies.com/gypsy-moth/
Rebecca, an EcoSpark intern, is a fourth-year student at the University of Toronto studying Environmental Science and Environmental Geography. Her passion for birdwatching keeps her outdoors quite often - learning the sights and sounds of nature. By writing this blog, she hopes her work on local citizen science projects can educate others interested in the field.
