Nature: Curve-lined owlet caterpillars have a remarkable ability to camouflage themselves

A curve-lined owlet dangles from a leaf in Adams County/Jim McCormac

Nature: Curve-lined owlet caterpillars have a remarkable ability to camouflage themselves

Columbus Dispatch
October 4, 2020

NATURE
Jim McCormac

The world of caterpillars is fantastically bizarre and their role in nature cannot be understated. Many of these creatures are by turns beautiful, outrageous, astonishing, and otherworldly. The fertile minds of Dr. Seuss or J.R.R. Tolkien could not have dreamt up some of these insects.

Caterpillars are one of four phases of a butterfly or moth lifecycle. Life begins as an egg, from which springs a caterpillar. Fresh from the egg, the larva will be so tiny as to be barely visible. But it is a plant-eating machine and grows rapidly through multiple molts. With each shed of its skin, the caterpillar emerges bigger. By the time this phase concludes, the caterpillar might be thousands of times more massive than when it began.

Next stop is the cocoon (moth) or chrysalis (butterfly), which is how many species overwinter. This is where a magical reorganization of tissues occurs. The caterpillar that formed the transformative chamber will eventually materialize as a winged adult, ready to start the cycle again.

Butterflies are chump change in this world. Only about 140 species have been recorded in Ohio. Moths? Try 2,000 or more species. And scores more await discovery.

The mortality rate of caterpillars is staggering. Some experts believe it hovers around 99% for many species. They are nature’s hotdogs and seemingly everyone wants a bite. Birds and other insects are especially voracious predators.

Astronomical kill rates have led to carpet-bombing reproductive strategies. Some female moths might dump several thousand eggs in the quest to survive the predatorial gauntlet to reach adulthood.

Bird predation, most likely, has spawned the evolution of fabulous camouflage in an enormous number of caterpillar species. Many of them hide in plain sight, but blend so well with their surroundings that even a sharp-eyed warbler might miss them.

On Sept. 6, I received a message from Chris Zacharias alerting me to his discovery of one of the grand prizes of the caterpillar world. Zacharias and his wife Sue are expert lepidopterists and sharp-eyed observers. They had discovered a curve-lined owlet caterpillar in a remote Adams County woodland.

I have searched for years for one of these extraordinary caterpillars, unsuccessfully. As have many of my entomologically-minded friends. Plans were made to seek the caterpillar early the next morning. Even though Zacharias found it a half-mile from the nearest road, his directions were explicit.

The next morning, I met naturalists Cheryl Carpenter and John Howard at the site. As we worked through the woods, we inspected the numerous greenbrier plants in the understory. Greenbriers are straggly shrubs in the genus Smilax. Curve-lined owlet caterpillars are specialists that feed only on these plants.

Suddenly a cry arose from John: “Here’s one!” Finally the spell was broken. We had found our larval Holy Grail. And it wasn’t even the caterpillar that Zacharias pointed us to, which we did find later.

As greenbrier foliage ages, brownish patches of necrotic tissue form, especially along leaf margins. Greenbriers also have tendrils to assist them in clambering over other vegetation. The curve-lined owlet mimics all these things, simultaneously resembling dead leaf tissue and greenbrier tendrils.

When disturbed, even by a gust of wind, the caterpillar will slowly twist and turn in the manner of a hanging dead leaf. Even the most sharp-eyed titmouse could easily overlook this potential meal.

This organism’s name stems from the moth, which has a prominent curved line across the wings. It, like its larva, is spectacular.

Caterpillars are a little-known but abundant part of the natural world. They are an endless source of fascination.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.

Curve-lined Owlet: A most extraordinary caterpillar!

 

A typical Ohio woodland, especially in southern Ohio's Adams County, where I made this shot. The leaves in the foreground belong to Common Greenbrier, Smilax rotundifolia. Many hikers/woods-people know this plant because of its heavily thorned stems. Walking through a dense greenbrier patch is not fun.

But greenbriers - there are about a half-dozen Smilax species in Ohio - are ecologically important and play host to some very cool critters. One of them, the extremely bizarre Curve-lined Owlet Moth caterpillar, has been on my hit list for years. I have searched scads of greenbrier, which sometimes seems like the proverbial needle in a haystack quest, to no avail. Until September 8. The quest caterpillar is actually in the greenbrier in the above shot, but might be a bit tough to spot. You'll certainly see it well in the following images, though.

Chris Zacharias knew that I and a few others were hot on the trail of this owlet cat, and soon after he stumbled into one at the location above back on September 7 (his first, I believe) he sent John Howard and I messages with details. And so launched my first ever major caterpillar chase, as it was a two hour drive to reach the site. But the following day I headed out at dawn, and met John and Cheryl Carpenter at the site. Our hopes were high. If some annoying titmouse or other caterpillar-killing bag of feathers hadn't taken out the owlet, we were pretty confident about finding our Holy Grail.

The Curve-lined Owlet caterpillar in silhouette. Even from this, we get a sense of the strangeness of this tubular oddity.

Chris, detail-oriented as he is - not to mention sharp-eyed! - had sent explicit directions to the cat, which was feasting on a greenbrier plant about a half-mile down a woodland path. We headed that way, but were slowed by numerous greenbriers dotting the forest floor. Figuring that the moth that laid the golden egg that produced Zacharias's owlet caterpillar probably laid scores of other eggs in the area, we carefully inspected plants on the way.

The three of us were gathered around a small patch of greenbrier, when suddenly John uttered magic words: "Here's one!" And just like that, the spell was broken. Years of fruitless quests and thorny greenbrier searches fell by the wayside, and we drank in the charm of what may be our (in Ohio, at least) most bizarre caterpillar.

The Curve-lined Owlet caterpillar hangs from a stem of Common Greenbrier, Smilax rotundifolia. Greenbrier leaves are often dappled with brownish patches of necrotic tissue, and leaf margins often turn brown and crisp. Furthermore, plants are beset with filamentous tendrils. The caterpillar seems to mimic all these things, and they can be incredibly hard to spot in the thickets. I shudder to think how many I've been in close proximity to, but missed.

A dead greenbrier leaf snagged on a stem. You can see how well the caterpillar mimics the look of dead plant material.

PHOTO NOTE: To get the uniformly brown bokeh (background) in some of these photos, we just held a piece of cardboard a foot or so behind the subject. I always carry such things - including sheets of other colors - to help separate my subject from a cluttered background when needed. I believe the greenish background in the previous shot was achieved by having John get behind the caterpillar so we could use his shirt for the bokeh.

After a suitable admiration session of the first caterpillar, we worked on down the trail and located Chris Zachariah's animal. Not one, but two Curve-lined Owlet cats in short order! This owlet was on a different greenbrier species, Bristly Greenbrier, Smilax hispida.

Their appearance is truly remarkable - look at those pseudo-tendrils! - but equally astonishing is the caterpillar's behavior. If disturbed, or even jostled by a puff of wind, the caterpillar will begin to slowly twist and turn, just as a hanging dead leaf will. John has great video of this leaf-mimicking behavior. I think the larva is aided in its ability to slowly twist and pivot from a single point by the fact that it has only two sets of medial prolegs - most non-inchworm caterpillars have four middle sets of legs.

Photo by John Howard and used with permission

If all goes well for the strange caterpillar, this is what it will become. The Curve-lined Owlet moth is also a very interesting insect. The common name derives from that prominent whitish line across the wings. I have never seen the moth, and appreciate John allowing me the use of his image. I believe he has seen only one or two of the moths. I too hope to some day clap eyes on one.

The seeming scarcity of this species is a bit of a mystery. Its host plants are common, and often locally abundant. Obviously the caterpillars, in spite of being of a decently large size, are tough to spot. But I and others I know have spent many hours looking for them and you'd think if they were fairly common we'd occasionally encounter cats. It's not like we're brand new to the caterpillar-hunting rodeo. Also, the moths don't seem to turn up very often at moth sheets. Perhaps they just are not strongly attracted to light, though. Anyway, some mystery surrounds this extraordinary animal.

Major thanks to Chris Zacharias for tipping us to his discovery. The caterpillar was everything we hoped for and more. Besides and as always, this foray got us deep into some interesting habitat, and that night we hunted more caterpillars and set up moth lights. Scores of other interesting finds were made and in all it was a highly productive long day of exploration and photography.