The Iris sawfly is a pest where the larval phase voraciously eats Iris leaves, and can be quite damaging, especially if present in large numbers. And this year they appeared in large numbers in some of our Iris beds.
The best method to remove them is manually. Put on some thin gardening gloves, look for the larvae on leaves (they can be both on leave edges and on the flat surface of the leaf) and just squish them. The larvae will tend to drop from the leaf when approached to quickly, but if they do, it is easy to find them on the ground and dispatch them there instead. Repeat the hunt daily until you find no more larvae.
And after you have purged your Iris beds of this pest, you can proudly say:
I pursued fly. I sawfly. I squashed fly.