Classic Hairy Vine

poison ivy on bark

This is particularly clear example of the hairy climbing vine that poison ivy often becomes.

The reddish hairs show nicely against the dark bark. And you can see both thick vine and thinner vines, plus one hanging off the right side that has no hairs at all.

Poison ivy seems very smart: it grows hairs when they are useful and not when they are not.

Are the hairs also dangerous?  Probably, to some extent, but since it is the sap that contains the dangerous urushiol oil, there is likely not much sap in those hairs. But if you cut into the vine itself, sap will ooze out, and that is the most dangerous stuff.