I haven't tried to verify species, but it does look like a Woolybear caterpillar, which turn into various types of Tiger Moths. Based on the photo and description, this one might be what is called the Salt Marsh Caterpillar, which can occur in large outbreaks, especially in early spring, and which will eat just about any sort of plant (including Irises). They are usually noticeable for a week or two and then gone. Later you might see lots of moths at lights that are white with black dots when the wings are folded, but which may have a yellowish hind wing.
It could be another species too, but I'm almost certain it is indeed of the Tiger Moth family or the Arctiidae.
They are hard to get rid of, because they are always on the move, and if you kill all of them in a yard one day, there will often be just as many new ones the next day. They (usually) don't do too much damage, and usually aren't around very long in a given season. Sometimes there are more than one big generation in a season, but usually it's only the first generation that is noticeable in it's numbers.
Date: Sun, 7 Jun 2009 20:39:22 -0400
Subject: Re: [iris-photos] What Am I??