I'm working out a bit of pseudo-story for something, and I've run across a question. I think I've got a partial answer to it, but I'm trying to figure out how well that answer would hold up under outside pressure, and I'm still trying to figure out the rest.

Foal, Filly, Colt, Mare, Stallion. What, precisely, would the proper equivalent terms for a changeling? I'm working with the following at the moment:
Foal::Grub (Extremely immature - on par with Pound Cake and Pumpkin Cake)
Filly::Nymph (Somewhat immature - on par with the CMC, DT/SS, or really most of Cheerilee's class)
Colt::Faun (Male equivalent to Filly::Nymph; think Snips & Snails, Rumble, Featherweight or Pipsqueak)
Mare and Stallion, as yet, I have no equivalent for. I may end up using those as direct counterparts.

Does anyone here see any particular problem with this logic, or have any better suggestions?

Well... it depends a lot on the headcanon, I guess. I've seen hive-structures with Drones, Under-Queens and Queens, and such, too.

I've also seen headcanons where the gender of changelings is completely irrelevant because none of them besides the fertile queens and mating males have any sexual identity at all.

I would say that nymph would be for colts as well and instead of being termed by gender, an adult changeling would be grouped by class:: drone, worker, soldier

this is just my own headcanon, so use what makes sense for the way you are portraying changelings

Male and female Changelings to me are just Stallions and Mares still

Given how large a part mimicry seems to play for changelings I'd honestly stick to the standard horse words.

Still, as long as you keep the bug inspired terms consistent it would probably work just fine.

It also depends on if you like to refer to the Changeling race as bugs. I like to think of them as changed ponies. So I use the Equestrian terms.

I use Drones and Workers for male and female. That's how they classify Bees. Drones are males while workers are non-queen females.

Or you could continue using Mare and Stallion. They are equin-ish.

My Changelings are actually one of the lost Kinds of Ponies. But they don't think of themselves as being so -- not until the Reconciliation.

Gender doesn't seem relevant, especially among drones.

Personally I keep it simple, since I too agree that changelings are a genderless race, and just call them hatchlings (instead of foal/filly/colt) and changelings/stallions/mares depending on their current form. Where it gets a little complicated is that I think the form shown in A Canterlot Wedding is actually battle fatigues, and not their "true" form.

Thank you for the discussion - it's revealed something I was thinking without explicitly stating.

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They're not 'bugs' per se, although they do acknowledge their insectile traits. (Not just appearance - a changeling's coming-of-age ceremony centers around the concept of their flight molt - the point when the chitin covering their wings is finally shed.) And for the notes I've put together for personal worldbuilding around them, the changelings never were ponies of any sort... although there is a connection in there.

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And here, we run into what's probably going to be my biggest problem with presentation, the point I mentioned earlier - that the way I see the changelings is apparently 90 degrees corkscrew from what the community consensus has decided they are. Consensus indicates that the 'proper' insect model for the changelings is from Hymenoptera - the order that contains wasps and ants - most of which are eusocial. That's not the impression I got from the show, though. To me, the changelings register far more as swarming beetles - visually, they sit somewhere between a rhinoceros beetle and a dung beetle, and I have trouble believing that a eusocial species could have been fooled by mere behavioral mimicry, as both Fluttershy and Dash managed. (I'd also argue that the individuality shown by the one facing Pinkie counts against it, but with Pinkie involved, I'm fairly sure all bets are off.)
This works into the question because, unlike ants or wasps, most beetles are explicitly gendered and do not behave on the 'hive'. There's no 'worker/drone/queen' setup like the eusocial insects have. This means that the eusocial terminology doesn't feel right to me, hence my attempt to find something else that would.

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If I remember correctly, entomology refers to an adult insect as an imago. Basically, a larvae becomes a pupa by making a cocoon or chrysalis, then comes out as an adult or imago.
As for headcanons, I am fond of changelings having poorly defined sexuality, and grubs being artificially developed into this or that speciality, like praetorians, infiltrators, carriers (runners of harvested love between feeding grounds and the hive), behemoths, etc.

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Oh, I know your headcanon... better than most here, probably. I was just pointing it out

Note that, as tosety pointed out, though, "nymph" is technically not a gendered word at all.

3699503 I just use normal equine pronouns because of my headcanon.

In your case, use "Drone" for adult males

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I've read a few where they're not the hive social structure, and I'd say a more fluid biology would work fine-- I've even seen the idea that changelings aren't even male/female, but are more hermaphroditic in their 'natural' form

I offered what I did because that's what comes to my mind and I can't think of any terminology for male/female insect distinctions apart from drone/princess

pick the term that works best for your story or even make one up. A different view of changelings won't kill a story for me