I once thought I was among the 20% of humans who experience no ill effects from poison ivy. But a visit to southern Illinois years ago proved me wrong. Itchy skin with blisters plagued me for weeks.

Still, I do not hate poison ivy and since that episode have learned to admire this plant that offers much to wildlife, especially in autumn and early winter.

A chemical irritant in the plant’s berries, leaves and stems, tricks the human immune system into attacking skin cells causing rashes and itching. Burning the plant can cause smoke that gets into human lungs and causes problems. Botanists speculate that the irritant evolved to help poison ivy defend itself from marauding beetles, caterpillars and slugs, or perhaps to ward off infection. It certainly didn’t evolve to keep humans away.

In fact, mammals such as deer and bears can eat the leaves with no harm, and more than 60 species of birds including catbirds and the yellow-rumped warbler migrating through our region now, eat the berries with no problems.

The key to living peacefully with, and even enjoying poison ivy, is to learn to recognize it and admire it from afar. Some scientists think that climate change may be increasing the population of poison ivy, as well as its potency to humans. So it makes sense to know where it’s at when you’re hiking in the woods.

Throughout the growing season, poison ivy leaves are composed of three leaflets with the middle leaflet typically longer than the other two. In autumn, the leaflets turn red, orange and yellow, and sometimes linger into winter as solid red leaflets.

Another vine-like plant, the Virginia creeper, also turns a lovely red in fall, but it can be separated from poison ivy in several ways. Virginia creeper has five, rather than three leaflets, and its vines are smooth while poison ivy vines are hairy.

Virginia creeper typically grows as a vine crawling up trees, but poison ivy also grows in shrub form or even as a groundcover.

In autumn, Virginia creeper produces dark berries, while poison ivy has clusters of tiny, less than quarter-inch-wide greenish-white fruits. Though Virginia creeper doesn’t cause bad skin rashes like poison ivy, it can cause some minor irritation, so it’s best not to touch either of the plants.

One of my most recent encounters with poison ivy was in a Lake County forest preserve this month. Yellow-rumped warblers, birds that migrate from the northern United States to the tropics in fall, were flitting around the poison ivy. Through my binoculars, I could see they were munching on its small berries. This fruit provides sustenance to this warbler species so that it can hang around longer and fatten up before heading south for winter.

At least four yellow-rumped warblers crowded on one tree branch to pluck berries from the poison ivy. Other migrating songbirds that linger longer in autumn also eat the berries, and I heard a gray catbird give its meow-like call while the warblers were feasting. Some biologists speculate that the chemical irritant in poison ivy somehow gets neutralized in the bird’s digestive system.

Other wildlife, including deer, eat the poison ivy’s leaves. Biologists think minerals such as clay and salt eaten by deer help neutralize the plant’s toxins.

In spring, small, native bees pollinate the flowers while getting some nourishment. And over the summer, larval insects actually use folded leaves of poison ivy to surround them when in the pupa stage.

It might be fun to look for those natural events come spring, but when doing so I’ll be careful not to touch this fascinating native plant.

Sheryl DeVore has worked as a full-time and freelance reporter, editor and photographer for the Chicago Tribune and its subsidiaries. She’s the author of several books on nature and the environment. Send story ideas and thoughts to sheryldevorewriter@gmail.com.