Why are there caterpillars everywhere 2022

Formerly known as gypsy moth caterpillars, these insects infested wooded areas of Ontario, Quebec and the Maritimes last year and it looks like they're back in action in 2022. Here’s everything you need to know.

If you’ve secured a coveted summer campsite and can’t wait to hit the forest with the fam, be aware that spongy moth caterpillars (scientific name lymnatria dispar dispar, or LDD, and formerly known as gypsy moth caterpillars) might have other plans for you. These icky insects, which were popping up on practically every tree in Ontario, Quebec and the Maritimes in 2021, seem to be back at it this summer—and we quickly learned last year that they don’t say on the trees. Families shared horror stories of the bugs raining down on them while outdoors, and others said caterpillar poop has landed in campsite meals (which then went in the trash). These pesky crawlers also pillage healthy trees of their beautiful leaves and can leave nasty rashes on human skin.

So what’s the deal with these things? Are they here to stay and ruin the rest of our summer plans? How can parents keep themselves and their kids protected? We chatted with Chris Darling, Senior Curator of Entomology at the Royal Ontario Museum in Toronto, and Toronto paediatrician Dina Kulik, last summer to get the full breakdown on our newest annoyance: spongy moth caterpillars.

What do spongy moth caterpillars look like?

Spongy moth caterpillars are dark coloured and hairy, with a double row of five pairs of blue spots, followed by a double row of six pairs of red spots down its back.

Why is Ontario seeing such an influx of spongy moth caterpillars right now?

Their populations rise and fall in a cyclical nature, so they build up, and then factors like weather and parasites (things that kill the caterpillars) bring them back down again. When natural enemies are low, caterpillar populations are high.

They’re everywhere right now, but in the coming days and weeks, they’ll transform into moths.

The cycle of these caterpillars infesting our trees is likely to continue pretty much forever, though, says Darling. “They’re established, effectively part of our fauna and flora now, so, they’re here to stay. In some years there will be more of them, some years there will be less.”

What happens when the caterpillars become moths? 

Luckily, we won’t have to worry about the moths bothering us too much. According to Darling, the moths will come out around July, fly around a bit, mate and and then die (the females lay their eggs first and then they die). The moths only live for a week or so.

Some families have described the caterpillars getting in the way of camping or cottage trips by raining down on parents and kids, and poop falling into campsite meals. Should families cancel these trips?

Darling says it really comes down to personal preference. “It depends on different people and different sensibilities so it’s hard to give a recommendation for everybody,” he says, adding we’re getting pooped on by caterpillars pretty much every time we’re in a wooded area anyway. “They’re out there, and not just gypsy moths,” says Darling. “There’s all kinds of caterpillars.”

If families are concerned about their food being contaminated, Darling recommends bringing a tent or tent-like structure (a mosquito tent, for example) for families to sit in while they eat.

Is caterpillar poop harmful to humans?

“There’s no suggestion whatsoever that it’s dangerous,” says Darling. Even if a child were to touch it (it looks like specks of dirt at a first glance, but closer-up the poop or ‘frass’ actually looks like tiny soil-coloured pieces of corn), there’s nothing to be concerned about.

Some people report getting rashes after touching a gypsy moth caterpillar.

It’s the small hairs on the caterpillar, otherwise known as setae, that can cause humans to develop a rash when they come in contact with the creepy crawlers. Darling advises parents not to let their kids handle the caterpillars.

Do the rashes affect everyone?

If a caterpillar happens to land on you or your child accidentally, you might luck out and not develop the rash since it doesn’t affect everyone equally. “Some people experience more local irritation than others, similar to other forms of contact dermatitis like poison ivy,” says Kulik.

How do you treat the rash if you end up with it?

Kulik recommends trying the tape trick, which involves applying a piece of tape to the affected skin and then pulling the tape off to remove the caterpillar hairs and reduce irritation. Beyond that, she says over-the-counter pain relievers like acetaminophen and ibuprofen (Advil or Tylenol) can help if there is pain, and a hydrocortisone cream or ointment can help soothe itchy skin.

Kulik says the rash doesn’t usually last more than a few days.

What does the rash look like?

It resembles welts or small vesicles (fluid filled sacs), with patches of red, scaly skin and raised red bumps, says Kulik, who adds that it can form within minutes or hours of exposure to the caterpillars and their tiny setae.

What can parents do to prevent their kids from developing the rash?

Aside from not touching the caterpillars, Darling says concerned parents could dress their kids in long-sleeved shirts and long pants, plus a hat, but that it might not be worth it. “Think about what’s out there causing rashes,” he says. “I’d be more worried about my kids trundling through poison ivy.”

In terms of deterring the caterpillars, do the burlap or duct tape tricks actually work?

If you have these pests on your property, try folding some burlap and using a piece of string to tie it to your tree trunk. The caterpillars then crawl up the tree trunk and get caught in the burlap fold. With a gloved hand and a bucket of soapy water, you can collect the stuck caterpillars and drop them in the bucket to kill them.

The duct tape trick involves wrapping duct tape around your tree trunk, taking care to press the sticky side into the trunk’s grooves, and then placing petroleum jelly on the shiny side of the tape to trap the caterpillars.

Darling says these strategies are actually more to protect the trees than to control the populations, as the spongy moth caterpillars can actually kill trees if they defoliate (eat the tree leaves) them enough.

What types of trees are they most attracted to?

Oaks are a particular favourite for the caterpillars, but Darling says they also like birch, aspen, sugar maples and even pine or fir trees.

So there we have it, the spongy moth caterpillar phenomenon explained. Even though they make our skin crawl, Darling says like most things—it will pass.

This story was originally published in June 2021.

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