Poison Ivy Has Its Plusses

by Jane Hill

Sycamore Islander, September 2000

Poison ivy can produce a skin rash if we touch its stem, root, leaves, or fruit. But this plant, a native, has considerable value to wildlife, which generally are not sensitive to its toxin, called urushiol. Poison ivy’s clusters of round, waxy, whitish fruits develop in summer and persist into winter, when they are of particular benefit to wildlife because of the scarcity of other foods at that season.

-- Drawing by Jane Winer      
At least 60 species of birds—including all of Maryland’s game birds and many songbirds—are reported to eat the fruits. This explains why poison ivy is common along fencerows and other places where birds roost—and leave deposits.

Local bird species that are known to eat the fruits include Eastern Bluebird, Gray Catbird, Dark-eyed Junco, Carolina Chickadee, Northern Flicker, Eastern Phoebe, White-throated Sparrow, Brown Thrasher, Tufted Titmouse, White-eyed Vireo, Cedar Waxwing, Carolina Wren, and Woodpeckers (Downy, Hairy, Pileated, and Red-bellied).

In addition, deer browse the fruits and foliage, and cottontail rabbits feed on the twigs and bark. The flowers are much frequented by bees.

Poison ivy grows across much of the United States, in southern Canada, and in Mexico, as well as in many other parts of the world. Because it is so widespread, and is not controlled in natural areas that many of us visit, such as parks or wilderness, it is important to learn to identify the plant, and to teach children to do so. You can learn to recognize it fairly easily by its alternate, compound leaves, each leaf consisting of three leaflets that are commonly toothed on the margins (though they are sometimes smooth). The leaflets are usually pointed at the ends, and the middle leaflet has a longer stalk than do the lateral ones. Leaves of a few other local plants also come in three parts, but poison ivy is one of the commonest. Therefore, teaching children to follow the old adage, “Leaflets of three, leave be,” will help steer them clear of the plant.

Another characteristic to look for is the growth form: Poison ivy can be either a trailing vine that sends up short, erect shoots, or a climbing vine that ascends trees and is “hairy” with aerial rootlets. In our area, avoid any “hairy” climbing vine because it is undoubtedly poison ivy. In addition, poison ivy has a close relative, poison oak, that is very similar in appearance but takes the form of a small shrub. It is also toxic, so using the “leaflets-of-three” rule will guard you against that plant, too.

In view of poison ivy’s wildlife benefits, and the incidental killing of other, nearby plants when chemical sprays are used to control it, poison ivy is best “left be” in natural areas.

Should you come in contact with the poison ivy or poison oak, wash with cold, running water as soon as possible to minimize the severity of the rash and help control its spread. Launder contaminated clothing.

Jane Hill, a botanist and a birder, contributed the article on Sycamore trees in the February issue. She and Bill are on the waiting list.