Spongy moth caterpillar crawls on a leaf

Caterpillar Rain

Insects dropped like rain from the trees.

The caterpillars, larvae of the spongy moth (Lymantria dispar), fell everywhere. Some landed on people’s shoulders, purses, and heads. Others hit the ground before crawling onto shoes, then upward on unsuspecting visitors to Allegan’s Oakwood Cemetery.

I can hear you uttering ugh. ick. gross! If you’re squeamish about insects… please keep reading anyway!

Oaks are a preferred host of the invasive spongy moth, whose larvae can defoliate a tree. It’s no surprise that a place called ‘Oakwood’ is a hotspot during our county’s huge spongy moth outbreak this year. Bert and I were at the cemetery for Allegan’s annual Living History Cemetery Tour, where actors portray notable citizens from Allegan’s past. Visitors swatted, squished, and picked the caterpillars off each other’s backs. But the actors didn’t flinch. Is that what they call getting into character?

Spongy moth caterpillar crawling on a hemlock branch
Spongy moth larvae don’t limit themselves to oak. This one picked a hemlock.

Things are less dramatic in our home’s wooded acre just a few miles from the cemetery. The critters are falling and crawling but on a smaller scale. Even so, I’ve squished them in the hundreds. And as I make my seek-and-destroy rounds, I do wonder: Where are these caterpillars’ natural predators?

The caterpillars are hairy. Touching them provokes an itchy rash in many humans, including me. So, I understand if nature’s pest-control pros are reluctant to scarf them down.

But quite a few species are known to prey on spongy moth caterpillars. The predators I see in my backyard include blue jays, orioles, starlings, robins, crows, nuthatches, chipmunks, stink bugs, spiders, and ants. Other predators are likely here, but I don’t notice them: ground beetles, various parasitic wasps, and the nocturnal raccoons and skunks.

The native defense team has no doubt helped reduce the invasive spongy moth population. Otherwise, I’d be squishing in many tens of thousands. A single spongy moth egg mass can contain up to 1,000 eggs.

In the spring, I didn’t find any bird nests close enough to monitor and film. So, I don’t have videos of parents feeding their kids this year’s caterpillars, spongy moth or otherwise. But I did find a few spiders that stepped up to the plate. Here’s one:

Spongy moth caterpillar wrapped in spider silk.
It took several days, but this spider eventually consumed the caterpillar.

I can also see the work of two unseen natural pest-control workers: a virus and a fungus.

The nucleopolyhedrosis virus, or NPV, attacks only the spongy moth. Caterpillars killed by this virus hang in an upside-down V shape from trees (and on my house’s vinyl siding). I’ve seen lots of these:

The lethal fungus, called Entomophaga maimaiga, causes the caterpillar to dry up while in a vertical position, head pointed down. Here are two. The one on the right is visibly dried up. The bigger one looked the same just a few days later.

Two spongy moth caterpillars hanging with heads down on a tree.

I find many virus- and fungal-infected caterpillars on our trees and siding. I leave them there on the advice of my conservation district. That way, the virus and fungus have a better chance of spreading and infecting other spongy moth larvae.

I’m grateful to my backyard’s spongy moth SWAT team. If this were a caterpillar-control competition, I suspect the virus and fungus would be tied for first place. But in my view, the real winner takes the prize in the best-effort category. Take a look:

The larva appears to have been squished before the ant found it. It seems unlikely that a carpenter ant could have done that to the caterpillar. Or do I underestimate an ant’s strength and tenacity? In any case, what do you suppose this ant’s nestmates think of its hairy contribution to their community pantry?

Resources and a Related Kids’ Book

Here’s a link to a spongy moth informational handout by the Allegan County Conservation District.

The district’s web page about spongy moths gives many more resource links.

Roscommon County, Michigan, also has an excellent spongy moth resource for homeowners.

For a kids’ book, I recommend Nature Out of Balance: How Invasive Species Are Changing the Planet by Merrie-Ellen Wilcox. This book is packed with fascinating facts and photos. It features compelling examples (called Invasive All-Stars) of non-native plants, insects, and animals that were introduced and then out-competed other, native species. The book is suited for kids about nine to twelve. I love how it presents the challenge of dealing with invasives. Using kid-friendly language, the text highlights the problem’s complexity: There are no simple solutions, and sometimes, a solution backfires. This is a great book for kids and adults alike.

Image Credits: Carol Doeringer.

2 thoughts on “Caterpillar Rain”

    1. There are so many of them, I had to do a deep dive to keep my sanity. And hmmm… maybe there is a book buried in the spongy moth saga!

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