I realize it's an entirely irrational phobia. Moths, caterpillars, and grubs absolutely horrify me. It's something to do with them having a combination of exoskeleton-like insect-y parts and soft, fuzzy, or squishy non-insect-y parts.
Actual bugs are OK (though I don't particularly like them). Snails are fine. Slugs are... less fine but tolerable. Moths, caterpillars and grubs make my skin crawl. Sea slugs are the absolute worst.
You're not alone. In the two cases I know, it's siblings who had a bad childhood experience, and now are both terrified of moths and butterflies. Their idea of hell is a butterfly exhibit!
Interestingly I know two people who are absolutely terrified of moths and cannot stand to even be in the same room.