You could use Bt (Bacillus thuringiensis). It's available at probably all garden centers and is sold under various brandnames.

If you get a blank look when you ask for Bt, ask for a "safe" or "organic" caterpillar killer. Alternately, read the ingredients list.

But, there's a glitch worth knowing about -- Bt works on caterpillars only until they are half-grown. Those now in my yard, are past that stage.

Thus, search-and-destroy missions about 10 pm are worthwhile. Cut the critters in half or flick into slightly soapy water.

The good news, though, is that two years ago I had a booming infestation, but the population leveled out on its own so that I now have minimal damage.

Thanks, Jean. I forgot about bt and never knew that there was a limitation on its effectiveness. Are these iris borers, or what are they called?

One of several caterpillars -- cutworms or the greater yellow underwing.

Doesn't really make any difference as to management. It's still search-and-destroy.