Spongy (LDD) Moth

How to identify the spongy moth

The spongy moth has four life stages: egg, caterpillar, pupa, and moth.

Egg mass

Egg masses are tan in colour, between the size of a dime and toonie. They are usually in tree bark crevices or other hidden places. It’s common to find them on vehicles, garbage cans, firewood piles, outdoor furniture and children’s toys.

Caterpillar

Caterpillars start off very small (about 2 mm) and molt three to four times, growing larger each time. By the time they reach their last molt, caterpillars can be 5-6 cm long. They are dark and hairy, with five blue and red dot pairs on the back.

Pupa

At the end of the caterpillar stage, the larvae seek safe shelter to pupate.

Adult moth

Female moths are white with dark markings and cannot fly. Male moths are light brown with dark markings and can fly.

History of the spongy moth

The spongy moth is an invasive species that is native to Europe. It arrived in North America as a result of a misguided attempt to create a domestic silk industry. It was first detected in Ontario in 1969. Its presence was met with alarm as the impact of defoliation became apparent. This defoliator feeds on a variety of hardwood species, preferring oak, birch, and aspen. During severe outbreaks, softwoods such as eastern white pine, balsam fir, and Colorado blue spruce may be affected.

Recent evidence, however, shows that spongy moths are behaving more like a native pest than an invasive species. This is due, in part, to the presence of several natural factors that help to regulate the population.

Why isn't the Town doing aerial spraying?

The County of Simcoe's research and resulting forecast predicts the spongy moth outbreak is in decline. The report did not recommend aerial spraying for county forests or municipal woodlands for several reasons. 

Timing

Aerial sprays require precise timing to be effective. Sprays require two applications within a very narrow time frame, which need to happen right after the caterpillars emerge and require specific weather conditions.

Cost

Aerial spraying over urban/residential areas is highly specialized and requires federal and provincial permits. Innisfil staff have limited capacity and in-house expertise to execute aerial spraying given the constraints of such work. Contracting out the service comes with a expensive price tag. 

Logistics

Despite the well-established safety record of Btk, some residents will oppose its use, creating logistical challenges where enough properties must be eliminated from spray blocks.

Natural controls

There are natural controls on spongy moth populations in Ontario, including:

• Cold temperatures
• Competition from other defoliators
• A natural fungus (Entomophaga maimaiga) known to contribute to spongy moth population collapse
• A viral infection (nuclear polyhedrosis virus or NPV) that kills moth larvae
• Natural enemies of spongy moth, such as parasitic insects and predators such as birds and mammals

These natural controls contribute the most to keeping levels within a normal range and tend to follow 2-3 years after the spongy moth populations peak.

Can spongy moth caterpillars cause allergic reactions?

Histamine found in the spongy moth caterpillar’s hair can cause red, itchy bumps to form. While the rash is not contagious, it can be quite uncomfortable. Wearing a hat, gloves, long sleeves and long pants can help protect your skin from coming into contact with the hairs. When handling caterpillars, egg masses and pupa always wear gloves to avoid an allergic reaction.

If you are experiencing any sort of reaction, please contact your family care physician for medical advice.

How do I scrape egg masses?

Please review this How To Sheet from the Invasive Species Centre for information on properly scraping and disposing of spongy moth egg masses.

Where can I purchase burlap?

We are not providing burlap for property owners. It is more readily available at local hardware stores and comes in different formats and sizes to meet your individual needs.

Watch this video from the City of Toronto for more information on using burlap to trap caterpillars.

How much damage can spongy moths cause?

Spongy moth caterpillars eat the leaves of trees, defoliating them. While most healthy trees can withstand several years of severe defoliation, trees that are already in poor health may have a harder time recovering. Additional stressors such as other pests and diseases or hot, dry weather may result in tree decline or death. 

If you're considering chemical treatments such as Btk-based products or TreeAzin, be aware that the effectiveness of these treatments at controlling the spongy moth is extremely time-sensitive. We recommend you consult with a private arborist as early as possible to allow the arborist time to properly schedule the work.