Boston Ferns are quite resilient when it come to cutting it back. Many people whack the entire plant back in spring, after being indoors all winter long, to get new growth and for repotting as well. I'm not sure what worm you have, since I've never run into any worm that would unless your talking about slugs. If you haven't found the critter, then I'd whack it back so you can look at the soil underneath to see if you can find it, which could also be a cut worm. The ones that curl up when touched. They hid during the day and come out at night. They do cause a lot of damage to plants as I found out this year with my Amaryllis. I couldn't figure out what was causing damage to the leaves until I found the cut worm neatly curled up way down at the bottom of the leaves. Out it came and I threw it away. But to get back to cutting back, whack it back and water it and watch the new growth come back up. Just don't cut too far back that you cut the growing tip off.
if you have the little runners you could let some root in another pot, if you're worried about it dieing. Epsom salts would probably be okay to use on the fern, but be careful of how often you do use it. Once or twice in a growing season should be enough. You don't want residue building up in the soil since ferns are not heavy eaters so to speak.
Good growing to you all out there, and lordy I go away for a few weeks and the messages pile up like crazy on me
