End in sight for caterpillar invasion

On these hot summer nights, there is always the soft sound of rain falling on leaves. Only, it’s not rain, it’s frass – the excrement from the Gypsy Moth Caterpillars that have invaded many parts of southern Ontario.
By now, locals will be used to being pelted by the hard round balls of poop, shredded leaves and the caterpillars themselves but it doesn’t mean they are not waging war on the gross invaders. With the pandemic, a heat wave and high water levels covering beaches, more people are looking for refuge in their own yards and the caterpillars are making that challenging, if not infuriating.
The caterpillars – which do sting – can be identified by their distinctive blue and red dots, but it’s not hard to locate them these days. They climb the trees to feast on the leaves at night and then they climb down onto the trunk during the day.
Rick Grillmayer, manager of forestry for the Nottawasaga Valley Conservation Authority (NVCA), said ​​​​​​​​European Gypsy Moths are an invasive species. The species is said to have been brought to North America in the 1860s, for a failed silkworm breeding experiment. First established in Massachusetts, they spread to Ontario by 1969.
“They go through these crazy cycles where the population explodes, and we are right at that peak, and then it collapses and disappears for about seven or eight years and nobody ever sees it and then it peaks again,” said Grillmayer.
“The caterpillars are now starting to pupate but most of the damage is done for the year.”
He said the species is a nuisance but are not as devastating to the forest as, say, the Emerald Ash Borer.
“As unsightly as it is, the Gypsy Moth doesn’t usually cause widespread tree mortality whereas Emerald Ash Borer kills all the Ash,” said Grillmayer. “That’s not comforting for someone who has a big oak tree in their backyard and it’s now completely stripped of leaves and their deck is covered in frass.”
Depending on the health and age of the trees, they are likely to survive the onslaught.
He said the infestation is in pockets, affecting Creemore, parts of Mulmur and other areas, but not the entire watershed.
“In an area where there is an extreme outbreak, I have seen them eat Spruce and Pine, which is a sign that there are a lot of them,” he said.
Grillmayer said they go after the Oak trees first and then move on to the Maples, and so on, indicating at what stage the infestation is at.
“Once it explodes and there are caterpillars everywhere, they will eat everything,” he said indicating the infestation is right at its peak. “They are eating everything, and that’s not usual.”
In Creemore, there is evidence of such widespread feasting but it will not go on indefinitely.
“[The population] is either going to collapse this year or next year or certainly the year after, but this is not something that is going to go on forever,” said Grillmayer.
For better or worse, depending on how you look at it, there are viruses and bacteria that infect the caterpillars and cause them to melt from the inside out. They drip down onto the leaves below and when the other caterpillars eat those leaves, they too become infected.
“It drives the infestation down and then it percolates there for seven to 10 years and then it explodes again,” said Grillmayer.
Although there are measures that can be taken, some are expensive, such as aerial spray programs. Individuals are taking steps to protect trees by wrapping the trunks in burlap or sticky tape, but many, including the NVCA, are simply letting the infestation run its course.
People can scrape the newly laid egg masses from the trees in the fall and winter, which are a spongy, fibrous material on the trunk, to minimize the next year’s population.
“It will get better, we will get through this. It’s the same message you keep hearing in all these different things, but it’s the same in forestry as well,” said Grillmayer.