The best DMs will allow it as an immediate reward and remember it for minor consequences later to progress the campaign in some way. "Druid knocked unconscious and taken while eating ants" type stuff
I love that you came back and added that edit, that's some commitment to keeping us up to date on the latest scientific breakthroughs about ant brains (I mean, I'd they have one?) and I appreciate it.
Honestly, this would be a lot of fun as a campaign. Starts off a normal group, druid played by the dm as a PC. Druid shifts, hijinks ensue, druid dies, and now the rest of the party has to battle their way across an unforgiven, sapient bug populated map, to reach the wizard's house to turn them back. It's only a mile away, but to them at their size, it might as well be the other side of the planet
Druids shouldn't be engaging in diplomacy anyway. Most of the druids I've known, thought that diplomacy = "destroy all cities and allow the forest to grow you humanoid bastards!"
Or ‘ants are enough energy for an anteater, but not a druid doing other stuff. Buff melee attacks/perception while in anteater shape, but nerf them in some way if they change or try to use magic in human form’
One of my favorite wizard characters was worried about rations, so I wrote into her backstory that she actually made an original 1st level spell for graduation of Wizard's School.
That went over like a Lead Zeppelin. The spell used a tiny touch of wild magic to "randomly multiply" the ingredients you had available. Just a single berry? You're getting a day's worth of berries. A carrot, a celery stalk, and an onion? Well you're getting all the fixins for a delicious vegetable stew.
The spell created magical food that couldn't be used as the material component for a further cast, and consumed the material components given. It then produced 1 day worth of vegetables, fruit, and berries, per caster level up to 5.
The headmaster and two other professors watched my character demonstrate her spell, at which point the headmaster immediately mind wiped the other two professors, and explained that I could only keep that spell if I swore to NEVER allow anyone else to see me cast it. Apparently it strayed too close to Clerical magic, and could have reignited the Wizard/Cleric War, that never actually happened, and actually turn it into a shooting war this time.
That particular character gave up on creating new spells till she was above 16th level.