Spider-changeling alt-species of changeling.
Some spiders cannibalize their moms upon birth for their first meal, this changeling variant does.
Spider changeling hunts other changelings. Captures them, they struggle, poison fangs them, they grow paralyzed, but can still feel everything Then we could go like an actual spider and suck them dry, but that's lame, a singular action, how boring.
Eating them alive sounds much more painful lol.

5946094
What`s the point? Spiders and their preferred methods are a product of evolution. Your spider-changeling, however? No logical way for it to evolve. Changelings by themselves are NOT comparable to flies - they`re more like termites. They stick together and act together. This calls for wholly different predator and mechanism of attack.
However, I`m... dubious about the likelihood of writing a reasonable aardwark-changeling either.

5946317 Changelings are infiltrators, so all you need to do is bait one with love, then theres the opportunity already. Termites? Ba.

5946517
They don`t operate as "one".
Besides, if spider had any idea about love, I would think they`d be a mite too preoccupied to bother luring stray changelings.

5947731 Who cares, there are liberties to making a fic for the sake of the idea. And spiders get rid of pest insects, that's how I got the idea. And since there are no shape-shifting bugs irl, I figure making the spider shape-shift isn't too much of a stretch. So, if you want a BDSM rather than grimdark, then you know where the spider would get its love. But this is a grimdark group, so idk why you care about that bit anyways, tho it could always be made in a kinky manner. Hmmm changeling chitin is a problem tho, I mean eating the flesh of ponies makes more sense, what you gonna do besides just drain a changeling, eat it like its crab meat I guess, or gonna have to take the whole thing apart.

5947895
Let me put it simply then. Horror does not work if the reader is constantly going "What the fuck, author?".
When you take too many liberties with suspension of disbelief, it ruins the mood of story entirely. Of course, you can do it on a purpose and call it comedy, but it takes a gifted author to pull it off well. Most attempts at this route end up just being "stupid stuff that sounds good if you`re baked".

5947988 Hm good point, prolly why they tend to take familiar characters, starting in a semi-normal setting.