I have read with some interest your various encounters with the dreaded
iris borer, but since I live in the Southwest it has not been a problem
here (fingers crossed).
However, on a visit to Chicago last week I found that my mother's few
iris had been decimated. We dug them and found the rhizomes badly eaten.
We also found a number of curious fat worms. They were about 3" long,
somewhat segmented, a little smaller than the diameter of a pencil on
one end and tapered to a point on the other. They were a dark reddish
brown in color.
I'm certain these were our culprits, but are these the borer or some
other devouring critter?