“Leaves of three, let it be”: that’s the old mnemonic warning for avoiding poison ivy. Spring is the worst season for running into the plant, or rather the sap it carries in the cells of its leaves. That’s because the new leaves, which are often reddish, are particularly thin and fragile. A light touch can breach the cells, releasing the toxic urushiol inside.
For those of us on the East Coast who curse the white-tail deer for browsing our gardens, decimating forest underbrush, and make driving hazardous, we can thank them for one thing. Deer are unaffected by poison ivy oil, and happily chow down on the leaves.