From what I know of earthworms they are likely not the problem but are ingesting the decayed material caused by the basic problem.

I haven't had this problem on my irises altho some of mine have spots on the leaves that are either a fungal or bacterial infection and I need to trim them all, wash them in bleach solution, and replant. I'll throw out a lot as I've let them multiply and they are too crowded. Huge job I've neglected as my best ones are not near those infected and are OK.

Have you checked out this link?

Here is a link that might be useful: pests and diseases of irises

Sounds like an iris borer may have done the initial damage and then an earthworm moved into the opening.. The link lucky gal posted has info on them. Scroll down past the disease section. Unfortunately it starts with this ominous warning:

"This critter is the scourge of the East and Midwest."

Yeap. It looked like that iris borer. Darn. we cannot use system insecticides here.

It's just as well that you cannot use systemic insecticides - they are suspected of being at least a contributing factor to the decline of pollinating insects like honeybees, bumble bees and butterflies. There are more environmentally responsible ways to keep your irises healthy:

1. Give them the proper environment: good soil, air circulation and sunlight.

2. Pest and disease problems that occur despite the above can often be addressed with simple hygiene: keep the garden clear of debris which harbors pests and diseases. Rinsing the rhizomes in a mild bleach solution (1 part chlorine bleach to 9 parts water) before replanting can also help reduce pathogens and pests.

3. Bacillus subtilis is a naturally-occurring beneficial bacteria that is now formulated for use in the home garden and is labelled for suppression or control of about 30 bacterial and fungal diseases. I have found it to be effective in my garden when used according to label directions. Serenade is one brand name, Bayer's Natria line has one as well.

The article linked below about growing irises organically may be of some help.

Irises seem to be as tough as they are beautiful. I hope a significant portion of your collection is unaffected and will return next spring.

Here is a link that might be useful: Growing Irises Organically