A brief essay in defense of poison ivy

A Yellow-rumped Warbler amid masses of poison ivy berries

The Columbus Dispatch
Sunday, February 2, 2014

NATURE
Jim McCormac

Not all animals let poison ivy be

“Mammals, a day of reckoning is coming. That’s right: The same plants and flowers that you saw crawl from the primordial soup will reclaim the planet.”
— Dr. Pamela Isley, aka Poison Ivy, a nemesis of Batman
 
Even the botanically illiterate know poison ivy. Toxicodendron radicans is probably the most despised plant in its range, which covers eastern North America. Plants in the genus are infused with urushiol, a compound that causes a blistering dermatitis.

We’re often rash in condemning the beautiful native plant. Poison ivy, if it were not chemically caustic, would make a fine ornamental. It often grows as a high-climbing liana, providing interesting ornamentation to its supporting trees.

The tired axiom “Leaves of three, let it be!” refers to the showy leaves, which are cleft into three leaflets. Many plants have leaves of three, but few are as showy as those of poison ivy. In fall, its leaves turn rich maroon — botanical fireworks punctuating the woodlands.

Come winter, clusters of porcelain berries become conspicuous. They arose from luxuriant panicles of greenish-white flowers that bloomed the previous spring.

Although people might overlook poison ivy flowers, the bugs don’t. Legions of valuable insect pollinators sate themselves on the rich nectar.

Poison ivy fruit is a wintertime staple for birds and other animals. The hardy yellow-rumped warbler depends on the berries to ride out the winter. So do bluebirds, robins, mockingbirds and many other species. A number of mammals also eat the berries, and others use the dense vines as shelter. These creatures are obviously immune to the itch factor.

So what is the reason for the plant’s toxicity? The itch-making urushiol wards off caterpillars, which are usually a plant’s greatest enemy. Urushiol is an effective deterrent to most of Ohio’s 3,000 species of caterpillars, which are the larvae of butterflies and moths.

But at least a dozen species have cracked poison ivy’s chemical code and can eat the plant with impunity.

Ironically, two of the ivy-eating caterpillars become gorgeous moths. The eutelia is a flying piece of postmodern art colored in chestnut, reddish-brown and white. The showy emerald is an exquisite moth clad in jade and trimmed with ivory stripes.

Ninety-nine percent of the poison ivy co-evolved caterpillars won’t make it to the moth stage. They will become bird food, just as will most of the ivy’s berries.

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