Ok, I did not know this. And I didn't even find out "the hard way", despite picking up all the fallen mourning cloak caterpillars yesterday like a giddy child grabbing the goodies from a smashed-open piñata.

And this afternoon, after I had already read the information on BugGuide, I picked up a couple more caterpillars by hand and still had no problem.

But just be careful anyway.