Isn't every day Mothra's Day? It certainly should be. I haven't watched the Simpson's regularly now for several years, but I'm not one of those fans who proudly proclaims the shows best years are way back. Still, it's rather hard to believe that the show has been on for 25 years. I know that beats Gunsmoke's record now. It's the "Longest-running animated American series, longest running American sitcom and longest running scripted prime-time series." All that is pretty amazing, overall, and I think it's fair to say it's an institution now.
It does have some blame in saving the Fox Network from insolvency, since it, along with Married with Children were the shows that lasted the longest on that fledgeling network's first couple season.
Anyway, Godzilla and friends have been featured and mentioned more than once, as is seen in this cute opening gag. I know we've actually seen Godzilla in the show, making me think Toho thought twice about suing another studio for copyright infringement, as is their wont to do these days. Mothra was in the gag about Monster Island "just being a name" since it was really a peninsula.