Sunday, October 4, 2020

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.

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