Doug Wechsler / Poison ivy vine (Toxicodendron radicans) climbing up White oak tree (Quercus) Fort Washington State Park, Pennsylvania, USA October

Doug Wechsler / Poison Ivy (Toxicodendron radicans) Schuylkill Center, Philadelphia, Pennsylvania, USA, April.

Doug Wechsler / Poison Ivy Sawfly (Arge humeralis) on goldenrod, Morris Arboretum, Philadelphia, Pennsylvania, USA, July.

Doug Wechsler / Poison Ivy (Toxicodendron radicans) climbing round tree trunk, Schuylkill Center, Philadelphia, Pennsylvania, USA, April.

Doug Wechsler / Poison Ivy (Toxicodendron radicans) on tree, Schuylkill Center, Philadelphia, Pennsylvania, USA, April.

Floris van Breugel / Traditional rock climber places a cam in Poison Ivy Crack, near Leavenworth, Washington, June 2013. Model Released

LYNN M. STONE / Chesapeake Bay Retriever in tangle of wild grasses, asters and poison ivy near saltmarsh; Waterford, Connecticut, USA

Doug Wechsler / Poison ivy (Toxicodendron radicans) in autumn, Carpenter's Woods, Fairmount Park, Pennsylvania, USA, August.

Doug Wechsler / Poison ivy (Toxicodendron radicans) vine on tree, Pennsylvania, USA, April.

Doug Wechsler / Poison ivy (Toxicodendron radicans) vine on tree, Pennsylvania, USA, April.

MYN / Piotr Naskrecki / Poison ivy (Toxicodendron radicans) leaves and tendrils, Concord, Massachusetts, USA, May. meetyourneighbours.net project

Doug Wechsler / Poison Ivy (Toxicodendron / Rhus radicans) flowers. Higbee Beach, New Jersey, USA, May.