Dear Mr. Alice:
We just came back from a very green vacation. Tramped through woods and fields and we all got poison ivy and were pretty miserable. But we also saw lots of animals around that didn't seem to be raiding our anti-itch lotion. Is man the only animal that gets poison ivy?
-- Lisa, out in the woods
Another advantage to being one of the higher primates is that we have a susceptibility to poison oak, ivy, and sumac. Dogs, frogs, not so much. In fact, a variety of birds and forest animals like bears, deer, rabbits, and muskrats find poison ivy berries and leaves pretty tasty fare. Their immunity to urushiol, the sticky resin in the plant's sap that causes all our miseries, could have been built up in the species since they need the ubiquitous plants for food. We, on the other had, have fish tacos and Milky Way Midnight candy bars. Grandma loves telling the story of the elf who scrubbed himself down with poison sumac to avoid a test at school the next day. Blew up like a Macy's Thanksgiving Day Parade balloon for about a week, but he never suffered from it after that. And remember that most animals have very thick fur that protects their skin from direct contact with urushiol.