The Naturalist's Journal

Cedar Waxwings are exquisite, black-masked songbirds that typically visit the ridge only in late-winter, but a recent infestation of foliage-devouring caterpillars, many of them the larvae of the Winter Moth, brought a large flock of Waxwings miraculously to the beeches, maples, oaks, and cherries to rid the trees of a true plague. 


In Salt Lake City, the faithful call it “The Miracle of the Gulls,” and, in countless retellings from Mormon pulpits, the story goes like this. In 1847, a band of pilgrims led by Brigham Young, the so-called “American Moses” and second president of the Church of Jesus Christ of Latter-Day Saints, arrived in Utah, and in the vicinity of the Great Salt Lake, set up shop and planted crops. The new arrivals harvested enough to make it through the winter, and the following spring, they planted again and gave thanks as the good earth started to nurture green. 

But in late May 1848, the pioneers made the acquaintance of another group of Utah residents: almost unimaginably large gatherings of “Mormon crickets,” which are actually flightless members of the Katydid family that go by the name of Anabrus simplex. These Shieldback Katydids may not be able to get airborne, but when conditions are right, they start to swarm en masse, and waves of A. simplex legions can travel more than a mile a day. The insects ingest everything green, sometimes including each other, in their path.

So it went that May, and it looked bleak for the pilgrims. But, in answer to fervent prayers, the Mormons were once again saved by birds. On their 1,300-mile trek west from Nauvoo, Illinois, to the Great Salt Lake, one group, in an 1846 Iowa encampment called the “Poor Camp,” were graced by the sudden appearance of multitudes of quail that provided sustenance, and in 1848, those swarms of crop-devouring insects attracted the attention of California Gulls, which swooped down and started devouring the pests. According to legend, the gulls no sooner ate their fill than they regurgitated the now-dead orthopterans and went back for another meal or two... or three... or enough to save the pilgrims from almost certain starvation.

I’m not a member of the Mormon congregation, but every naturalist is more than familiar with this story, which, at its ecological heart, is about the way nature tries to curb what are known as boom-bust cycles. The tale certainly came to the fore recently, when we experienced a similar example of irrational exuberance, natural history style, on the ridge.

For the past five or so years, no sooner has the green foliage curtain begun to descend than a mind-boggling overabundance of insects started turning the leaves to, well, caterpillar poop. The perpetrators of this defoliation are, of course, larval Gypsy Moths.

These terrible creatures were, as is by now well known, introduced into this country as a result of an experiment gone awry when, in the late 1860s, a French-born entrepreneur named Etienne Leopold Trouvelot brought a batch of caterpillars from their native Europe to his adopted home in Malden, Massachusetts, to try to establish an American silk industry. We know what happened next—and has occurred repeatedly, in a classic boom-bust cycle fashion, since then. The most recent Lymantria dispar plague has resulted in the deaths of thousands of area hardwoods, but the cold, wet springs we’ve experienced for the past couple of years have made growing conditions ideal for a Gypsy Moth–killing fungus called Entomophaga maimaiga that was imported here from Japan several times since the turn of the past century and now seems, if the weather is right, to be able to occasionally thwart an L. dispar outbreak early.

But as the tree canopy thinned, I scratched my head and put on a hat to ward off the light rain of caterpillar frass. At least it wasn’t as bad as in other years, when what we experienced approximated a hailstorm.

Because of the fungus and an equally lethal virus, I know these out-of-control defoliators weren’t young Gypsies. To learn their identities, I had to match the larvae with the images and accounts contained in the Bible of the trade: University of Connecticut entomologist and insect wrangler David L. Wagner’s Caterpillars of Eastern North America. The Princeton University Press field guide is one of those must-have books that belongs on every naturalist’s bookshelf, and I consult it often, since I’m forever running into caterpillar species I don’t know.

One of the likely suspects bore a telltale line of tiny white “footprints” on its back: a clear field mark of a Forest Tent Caterpillar. Malacosoma disstria is a native species of our woodlands, and is, notes Wagner, “an occasional forest pest.”

More likely, however, was a way-too-abundant inchworm-type caterpillar that would, if unchecked, give us yet another horde of Winter Moths at the Christmas lights. Operophtera brumata is, like the Gypsy Moth, an introduced species, and during outbreak years, as this one appeared to be, the caterpillars can denude large swaths of forest-tree foliage. Nothing much, as near as I can determine, controls the critters.

Well... then I discovered the Miracle of the Cedar Waxwings.

Waxwings, so named because of the brilliant red wax droplets on the edges of the wing feathers, are songbirds that often bless us with their presence during the cold times—they like to dine on winter-softened holly berries—and then disappear during the good weather. But in late May, when the defoliation was becoming alarming, I heard the telltale high lisps in the tree tops that, I knew, could have come from only one source.

Normally, when I spot waxwings, I’ll see, at most, six or so, but here on the ridge, there were suddenly dozens, each of them gleaning something from the leaves. A few of the birds favored me by coming down quite low and letting me watch them. Clearly, they were harvesting small caterpillars. I’m reasonably certain we both knew the species.

The waxwings were in residence for several days, and when the flocks finally departed, hopefully in the direction of another infestation, it was difficult to find any Winter Moth caterpillars. That was fine by me. When I searched the ridge for the stunning pink blossoms of the Lady’s Slipper Orchids or the pastel shades of the Dame’s Rocket flowers, the latter of which I hoped would attract Spicebush Swallowtail butterflies, Nessus Sphinx hummingbird moths, and various intriguing other insects, from true bugs to flower flies and native bees, I no longer needed to wear a hat.

Maybe the sudden appearance of the Cedar Waxwings wouldn’t serve as the foundation story from which I might craft a new religion, but it’s a “miracle” I’ll take to heart. And, of course, to my un-chapeau’d head.

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