Thu. Dec 7th, 2023
Very hungry caterpillars

Note: This blog is about the non-native and highly invasive moth species Lymantria dispar dispar, which we previously referred to as the gypsy moth or by the acronym LDD. In this article, we will refer to the moth using its new common name, Spongy Moth.

If you’ve seen an Ontario oak tree recently, chances are you’ve been introduced to the invasive fluffy moth (Lymantria dispar dispar).

Fluffy moth caterpillars were first introduced to North America in the late 1860s and are voracious eaters. Their favorite cuisine is oak leaves, but in particularly bad outbreak years, like this one, they can spread to many other tree species.

How do I protect myself and my campsite?

We know many visitors have questions about this and may be wondering what to do if there are fluffy moth caterpillars in the park during your visit.

When it comes to camping comfort, avoid handling the tracks with bare skin. They do not bite, but their hairs can be irritating and cause rashes.

You should also bring a tarp or eating shelter for your campsite rest area. Tree leaves are high in fiber and these caterpillars are certainly feeling the effects.

Leave me alone, moth!

ChrysalisOnce satiated, the caterpillars will pupate in July.

The caterpillars (or larvae) of the fluffy moth change as they grow. Young caterpillars emerge from egg masses in late May and feed on leaves until early July. Mature caterpillars can measure up to 2.5 inches.

As caterpillars go through their life cycle, trees may seem to lose their leaves overnight. This often causes campers and visitors to worry about the health of our park’s trees and ecosystems.

Although insecticidal sprays exist, they are very expensive.

Bacillus thuringiensis (or Btk), the product commonly used to control fluffy moth outbreaks, can kill other lepidopteran caterpillars (butterflies and moths) when the spray is applied. [1] [2]

Although the timing and method of application can minimize impacts on some species such as monarchs, Ontario is home to more than 1,600 species of butterflies and moths, many of which are found in their larval form at the same time as fluffy moth caterpillars. .

Butterfly and moth caterpillars are vitally important in June: they are what almost all of our breeding bird species feed to their young. A single black-capped tit pair needs thousands of caterpillars to raise a single clutch of chicks. Many of the butterfly and moth species are also rare and need protection.

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Decisions about managing invasive species often require balancing various land values. Other land managers may decide that spraying is necessary to protect their trees.

Ontario Parks has decided not to risk potential impacts to other lepidopterans, so there are no plans to spray for Spongy Moth in any provincial park this year, but spraying may occur outside park boundaries. Ontario Parks environmentalists and park managers will continue to closely monitor the situation in the future.

Should we worry about trees in parks?

Fortunately, healthy trees are quite resistant to these leaf eaters. [3]

Although losing their leaves means the trees won’t be able to grow much this year, many will develop a second or even third flush of leaves later in the season.

Our trees also have an army of natural defenders. Birds such as yellow-billed and black-billed cuckoos, blue jays, orioles, and eastern towhees find the caterpillars of the fluffy moth delicious, while small mammals such as mice and squirrels eat the pupae.

Beneficial wasps parasitize the egg masses and black-capped tits feed on the eggs during the winter. [4] Cold winters are another nemesis of Spongy Moth; Their eggs often do not survive when temperatures drop below -20°C for prolonged periods. [5]

As an outbreak progresses, more devastating natural controls begin to act.

Two diseases, nuclear polyhedrosis virus (also known as NPV) and a fungus called Entomophagous maimaiga It spreads easily through fluffy moth populations during outbreak years. [6] [7] Between predation and disease, populations typically collapse within a couple of years.

The Ministry of Northern Development, Mines, Natural Resources and Forestry is monitoring fluffy moth outbreaks in Ontario. You can find the results of their survey and more information about this species on their website.

How I can help?

This is something our trees have seen before and will see again. But there are many things you can do to help:

gypsy mothfemale fluffy moth

Act on climate change. The effects of invasive species like the Spongy Moth may worsen with climate change.

Fluffy moth outbreaks are associated with warm winters, while cool, wet spring conditions promote the spread of natural fungi in the population that play a key role in population collapse in outbreak years. Climate change alters weather patterns that keep many invasive or potentially invasive species in check.

Fluffy moth eggs can die in sustained cold temperatures, so continued warm winters may lead to more frequent outbreaks in the future or additional stress on trees.

Do not move firewood long distances.. While the fluffy moth, emerald ash borer, and other pests may already be living at your destination, there are many others we want to keep away. A single piece of infected firewood can destroy millions of trees. Purchase your firewood at the park office when you check in at your campsite or purchase it from a local park supplier.

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Educate yourself and others about the threats to our trees and forests. In particular, our now weakened oak trees are in danger from oak wilt, an invasive fungus found just across the Canada-United States border.

To help prevent infection, landowners and land managers should avoid pruning or cutting their oak trees between April and July. When visiting Ontario parks, let a park staff member know if you see an oak tree dropping its leaves in July or if the leaves are browning at the tips.

gypsy moth

It’s better to prevent than to cure

Once an invasive species establishes itself in an ecosystem, control efforts can sometimes do more harm than good. In this case, we should learn the lesson that prevention is better than cure and focus on keeping new invasive species out of Ontario.

We love our trees, but remember: they are just one part of our parks’ biodiversity networks. Our incredible park staff work with insect and forest specialists to protect all the ecosystem connections that make life in Ontario possible.

Let us remember that when it comes to invasive species, prevention is vital. Show that the trees you care about keep new invasive species out of our parks.

[1] Heimpel AM and TA Angus. 1959. The site of action of crystalliferous bacteria in the larvae of Lepidoptera. Journal of Insect Pathology 1: 152-170.

[2] Broderick, N.A., C.J. Robinson, M.D. McMahon, J. Holt, J. Handelsman, and K.F. Raffa. 2009. Contributions of intestinal bacteria to thuringian bacillusInduced mortality varies in a variety of Lepidoptera.. BMC Biology 7(11).

[3] Eisenbies MH, C. Davidson, J. Johnson, R. Amateis and K. Gottschalk. 2007. Tree mortality in mixed pine-hardwood stands defoliated by the European gypsy moth (Lymantria dispar L.). Forest Sciences 53(6) 683-691.

[4] McCullough, DG, KA Raffa and RC Williamson. 1999. Gypsy Moth’s Natural Enemies: The Good Ones! Extension Bulletin E-2700, Michigan State University Extension.

[5] Andersen, JA, DG McCullough, BE Potter, CN Koller, LS Bauer, DP Lusch, and CW Ramm. 2001. Effects of winter temperatures on gypsy moth egg masses in the Great Lakes region of the United States. Agricultural and Forestry Meteorology 110(2001) 85-100.

[6] Podgwaite, JD, KS Shields, RT Zerillo and RB Bruen. 1979. Environmental persistence of gypsy moth nucleopolyhedrosis virus. Lymantria dispar. Environmental entomology 8(3) 528-536.

[7] Andreadis, TG and RM Weseloh. 1990. Discovery of Entomophagous maimaiga in the North American gypsy moth, Lymantria dispar. proceedings of the National Academy of Sciences 87 2461-2465.