Pacific Northwest | April 18, 2004Pacific Northwest MagazineApril 18, home
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They're back! Creatures only a Mother could love
AH, EARTH DAY. Time to remember our reverence for the planet, to honor and cuddle close to the nurturing bosom of Mother Nature.

You love Mother Nature, you say? Just how much do you love your mother? Shall we put it to a little test?

Picture, for instance, writhing masses of Malacosoma californicum chewing their way through your rose garden. If grossness had a Richter scale, a full-on invasion of Western tent caterpillars is an easy 10.

Oh, a few caterpillars here and there, sure, no big deal. But that is not what we are talking about. No, we mean the special treat some of us enjoyed last spring — at Alki, in Discovery Park, on Vashon Island.
For more on the biology and control of caterpillars, visit:

Washington State University

Washington Toxics Coalition

For questions about tent caterpillars in Seattle parks, call 206-615-1660.

For every year in Pugetopia, somewhere, there comes a time when we must also reckon with our baser instincts, awakened by infestations of tent caterpillars. Biologists coolly refer to these as "outbreaks." More precisely, it's when Mother — remember her? — detonates her bio-bomb of squirming hairy hordes.

We're talking every alder in the neighborhood toilet-papered with caterpillar tents.

Tent cats are always around, but their populations are mobile and variable, booming to plague proportions in isolated hot spots. These heaviest infestations usually peak one year and dissipate over the next two as pests and diseases do the caterpillars in. Then the predators, starved for food, die off and tent-cat populations rebuild once more.
Tent caterpillars are ingeniously equipped to deal with predators. They spin a protective tent to hide during the morning and evening hours when birds are feeding. They come out during the day to gorge on leaves.
The cycle repeats endlessly, but it's a moveable feast. Moths that lay the eggs for next year's outbreak are always traveling to new ground. Scientists debate whether there is any predictable pattern or interval to the cycles.

But there's no mistaking when the party is at your place.

Waves of caterpillars wash up the sides of the house; conga lines of caterpillars cha-cha on the porch furniture, their little bodies twitching with eagerness to latch onto the next surface — perhaps your flesh?

Because tent caterpillar outbreaks are never region-wide, some of us always think the rest of us are exaggerating as we rant, in this our deeply troubled world, about something so mundane, caterpillars. Some of you are probably thinking, really, it couldn't have been that bad.

But we know better.

We huddled at Metro bus stops and park-and-rides and grocery stores, picking reflexively at our sleeves.

And as we talked, it was no ordinary neighborly exchange, but a cathartic, primal scream: the Caterpillar Diaries, the telling of our daily hell of Living With Mother Nature.

In this 1947 photo, a Parks Department crew sprays arsenate of lead on trees around Green Lake to kill tent caterpillars. Parks officials say they rarely use insecticides on tent cats today, relying instead on natural controls.
It was a surprise, this invasion.

Who knew those dingy gray, Styrofoam-like bumps we saw clinging to just about every branch and twig were actually the casings of hundreds upon hundreds of caterpillar eggs?

We would muse at those odd forms, wondering what they were. Ponder, mildly, were they anything we needed to do something about? Or just another interesting aspect of Mother Nature?

And there were so many other things to do, so we let it all be. But how odd, we thought, that we had never seen them before. And there were so many.


Warm days at last, and long, sweet daylight.

But what's this? Gauzy tents suddenly festoon the fruit trees. We look closer and see them full of tiny wiggling worms.

Increasing daylight hours of spring, combined with warmer temperatures, have opened what biologists call the circadian gate. Larvae locked in protective egg masses all winter are hatching out. The timing is perfectly aligned to the unfurling of tender new growth on which the young larvae thrive.
Photo  Photo
Tent-cat egg masses (top left) survive winter ice and snow with aplomb, hatching out to wriggling larvae.
Weird, we think, and brush a few off, grinding the worms into the bark of the branches with alacrity. We don't bother with the ones that are hard to reach. We're busy, after all.

But soon the jig is up, those little worms are no longer little. And no longer contained in their tents. They're on the move now, thousands of them, devouring new growth on the cherry trees and making the very leaves of the hawthorn tremble as they strip it bare.

We want to let nature take its course. We root for the birds.

But the caterpillars have the birds all figured out. Northwest natives, tent caterpillars are ingeniously equipped to protect themselves. They extrude a protein material from their mandibular glands that, on contact with air, hardens into fibers for knitting up a cozy tent.

Very clever: The caterpillars huddle in the tents in the early morning and evening, when the birds are feeding. They disperse to chow down only during the day, laying down a pheromone trail as they walk to find the way back to their tents before the birds' dinner bell.

In no time at all the alders are stripped naked. We figure out, too late, this caterpillar thing is not going to be contained at the edges of our busy little lives. This is a plague of biblical proportions.

The caterpillars, out of alder and hawthorne leaves by now, are on the march. Their attack is not random: They target favorite foods with ferocity. Theirs is a shock-and-awe campaign in the league of locusts, cicadas and army ants. Ash trees, birches, cottonwoods, willows, fruit trees and roses — foliage shredded to lace. Do they even sample the Scotch broom and other plague plants? Of course not.


Within five to six weeks, the larvae are 3-inch-long caterpillars — fat, juicy and robust, molting four times to accommodate their growth. At the bus stops, the grocery, the post office, we share dark fantasies filled with moats of flaming oil; blazing oxy-acetylene welding torches, and squadrons of crop dusters letting loose bellyfuls of Dow Chemical's best.
One beleaguered island couple chronicled the invaders' march across their porch and onto their usually inviting wooden bench.
We put twigs laden with wriggling nests to the flame and love every minute of it. We drive over pavement writhing with caterpillars and lower the windows to listen to the squish.

We spend our Memorial Day weekend on search-and-destroy missions, nailing caterpillars with a splat between thumb and forefinger in a vain attempt to defend the roses.

We keep at it until our gloves are soaked. Until we are buggy, twitchy, swatting at our ankles, whacking at our pant legs, until we can't even look at a pattern on a shirt without an involuntary lurch of the stomach. Until we wake ourselves up at night screaming, "DON'T TOUCH ME!"

Guests? Out of the question. No one could even sit on our porch furniture, alive with wormy, hairy mats of caterpillars. Lie on the grass? Pull an Adirondack chair under a tree for a snooze? Anything but that.

No one in the city has any idea what we are talking about.


For the first time ever, as we commute downtown to work, we can't wait to get there.

We long to take cover inside those sealed buildings, surrounded by concrete and asphalt. By now, even a landscape strip with a few scrawny shrubs makes us uneasy.

Hardest hit are those of us who have chosen to live closest to Nature, deepest in the woods, erecting our King County Stewardship Forest placards with pride.

"Condo! Condo! Condo!" chants one such neighbor as she sweeps tents from the mantelpiece. The caterpillars crawled there and set up house after her partner, planning a festive little caterpillar roast, put infested twigs in the fireplace.

Not that you could keep the caterpillars out if you tried: They hitchhike in on the dog, cling to our clothes. Surge under the doors. No problem for a beast with all-terrain gear: six articulated legs on the thorax grasp and climb, and suction feet provide traction in the back. They can climb upside down, scoot along edges, reach out into space and grab onto the next leaf or haul themselves over grass, gravel, beach sand, plate glass, any surface at all.

Their bodies are so light-weight no thorn will puncture them, and so flexible and sure-footed no corner, twist, turn or slope is too tough to negotiate.

We find caterpillars wriggling on our pajama tops in the morning. We encounter them rearing up on our lovers' collars, as once indoors and finally able to relax — we thought — we lean in for a kiss.

Worst are the warm days drenched with sun, the ones we longed for all winter. But the heat makes the cold-blooded caterpillars go faster. They ripple across the porch and chew through the foliage like wood chippers.

Sure we love nature. But what about our roses, our strawberries and fruit trees? Our sanity?

Mostly, we love it when the local bar holds a caterpillar stomp. And we are not surprised when the hardware store sells out of bug killer, and not just the Earth-friendly stuff.

"Some people bought 'em two at a time," says the clerk gesturing at the shelf where some reached for the chemicals we are Too Pure to Use when in a normal state of mind. Which we are not. "People are fed up," she says.

No kidding: We walk our dogs in the woods and realize that sound of rain is actually a deluge of tiny caterpillar scat pelting shredded leaves.

A weird nuclear-winter look afflicts the alders — strafed, stripped, bare, even as summer bursts out all around. The summer everyone else is enjoying.


Suddenly, tan, cottony wads are everywhere; tucked under the flashing of the house, crammed between the boards of the deck, stuck in the porch light. The tent caterpillars, sated at last, have spun themselves inside cocoons the size of a shelled peanut. In about 10 days they will metamorphose and emerge as dull brown moths. We don't even get butterflies out of this deal.

But we love watching the birds gobble the moths; the swallows make spectacular mid-air kills, nailing the slow, wallowing moths in a single gulp.

Soon we see the ubiquitous egg masses that puzzled us before, but this time it's no more Mr. Nice Guy, we know where all this is headed.

The more vengeful among us will spend the winter rubbing the moth's egg casings off the fruit trees and rolling burlap like battlefield medics, the better to swaddle our trunks, and paint them with goo to snare a million moving legs come spring.


This year, it seems so odd to dread spring, but those most versed in the Caterpillar Diaries do.

What is it, exactly, that is so gross about these bugs? They don't bite, don't sting, don't smell, aren't poisonous, don't carry diseases to people or pets or livestock.

Maybe it's the way they reach out for the next foothold, wagging side to side. Or the bristly hairs all over their body, so useful for deflecting parasitic wasps and flies. Is it the sheer seething, uninvited, disgusting disruption of it all?

We call around, trying to figure out what to do this year. There's no reason to reach for the hard stuff, botanically (or alcoholically) speaking, the experts tell us. Most trees will recover even if completely stripped. There's also a positive side to these invasions: Trees that do succumb make space and let sunlight in for newcomers, which contributes to plant diversity.

All that caterpillar scat feeds the soil, and Western tent caterpillars are an abundant food source for birds and bats.

Besides, time, ultimately, is on our side.

The trees, once stripped, change their chemistry and become harder to attack. Caterpillars don't feed as well the next time around — even as they face increasing assault from disease and predators that thrive on the bumper crop of bugs.

Our favorite is a tachinid fly that lays its eggs in a little white dot on the head of the caterpillars. The eggs hatch into maggots that burrow into the caterpillar and start feeding. Most satisfying.

Yes, the experts say soothingly (from inside their sealed offices) these outbreaks are natural, part of a cycle that has its own logic and rhythm, in which our chemical concoctions should have no part.

While many of us, including the Seattle Parks and Recreation Department, used to spray these outbreaks into submission, we now know better. Those satisfying instant-death sprays are toxic not only to all caterpillars but to birds, mammals, honeybees and other beneficial insects.

The official policy among the folks at Seattle Parks, once those eager dispensers of arsenate of lead? "If you think of it as part of a natural system, it helps," the department's Barb DeCaro says. These days, the department keeps insecticide use on tent cats to a bare minimum, mostly relying instead on natural controls, she says. "In spite of the fact that in large numbers they are gross, we really are better off if we allow these things to happen."

So if this is your year to host the caterpillars, just try taking that to heart. Go ahead. Celebrate spring, drink a toast to Earth Day.

Just remember to chink a towel under the door unless you want lots of company.

Lynda V. Mapes is a Pacific Northwest magazine staff writer. Tom Reese is a Seattle Times staff photographer.

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