I have grey-green fairly large caterpillars eating my foxgloves. They are eating them to shreds but I have hopes that they will still flower. They are leaving what looks like rodent droppings in the leaves. They are eating only the foxgloves. My question is what are they and is it okay to keep the plants or should I pull them up?
I strongly suspect you have variegated (or climbing) cutworms. I have these nasty bugs too and can give you a long list of plants they eat. Foxgloves are their favorite. Here are some management solutions in order of most work, least toxic to less work, but more toxic:
1) hand-pick after dark (with a flashlight) starting in January and continuing through May.
2) spray Bt (Bacillus thuringiensis) (found in Caterpillar Killer). It must be reapplied after rain. Be careful where you spray it because it will also kill butterfly caterpillars.
3) general pesticides will kill cutworms and many other critters that come along, including bees and may harm birds.
Here are some links to more information:
U.C. Davis Integrated Pest Management
Oregon State University Department of Horticulture