Godzilla: King of the Monsters made a big addition to Mothra's arsenal by giving her a stinger, but why was this change made? Mothra never had a stinger in any of Toho's classic Godzilla and Mothra movies, nor does the insect that the character is inspired by come equipped with one, either.
Godzilla: King of the Monsters added three Toho kaiju to Legendary's MonsterVerse with the introduction of Ghidorah, Rodan, and Mothra, who have all been associated with Godzilla since the 1960s. The new movie kept the basic designs for all three monsters to make them easily recognizable, but also made a few slight (but important) adjustments. Rodan was updated with a new look that is both fiery and menacing, Ghidorah received a design that allowed for better mobility, and Mothra was given longer, clawed forelimbs and a deadly stinger.
During a Godzilla: King of the Monsters watch party, director Mike Dougherty explained in a tweet the reasoning behind Mothra's new stinger. According to Dougherty, it "was born from the concept that she lived in a pretty vicious environment full of predators and would need an equally harsh method of self defense" [via Twitter]. Dougherty also added that Mothra's stinger is possibly how she lays her eggs, and joked about the idea of Rodan now being pregnant (since he was stabbed with it at the end of the film).
Dougherty makes a good point about Mothra needing a weapon to defend herself with, considering that she lives in a world full of predators. It's possible that in the thousands of years that Mothra has been around, being reborn time after time, the evolutionary process caused her to adapt to the world around her, and gave her the tools she needed to survive in a place full of creatures like Rodan, Ghidorah, and all of the unseen Titans in King of the Monsters. In Toho's movies, Mothra's primary tool against other kaiju was her silk, which she used to bind her opponents. Granted, it's come in handy a few times, even against Godzilla himself in Mothra vs. Godzilla, but it's not much of an offensive weapon, and is more of a restraining technique. As a creature of a beauty - more so than a force of destruction - Mothra has never been as dangerous as other Toho monsters, nor was she ever supposed to be.
Fortunately, the addition of the stinger in King of the Monsters doesn't change this element of Mothra too drastically, and just gave her something that put her on a more even playing field with the other Titans. It also created a fun, surprising moment when it was used to impale Rodan in the movie's final battle. And while it may force enemies to take Mothra more seriously than before, it doesn't alter the image of Mothra presented in Godzilla: King of the Monsters. The third MonsterVerse installment succeeded in staying true to Toho's vision of Mothra as a peaceful and benevolent Titan devoted to keeping the balance and protecting the world.
