Pittsburgh Post-Gazette: Poison ivy's shiny green leaves are gourmet cuisine for deer, bear and other animals. Birds like its white berries and spread the seeds by unmentionable means. But the leaves, berries and vine are the bane of humankind and primates. In the hours after the lacquer-like oil, urushiol, gets transferred at the slightest contact, mad scratching begins.
Enough urushiol to fit on the head of a pin can cause misery for 500 people. Even a billionth of a gram of urushiol on the skin is said to cause agony....