We know that Hordlings are "born" from larvae (usually, at least), quite much like fiends on other planes are.
We know that Night Hags herd larvae, using them as trading stock and evil planar currency.
What we don't know is, what Night Hags think about Hordlings, how they are connected with them, why the hell they ever began herding larvae, if they like, dislike, love or hate Hordlings, and what Hordlings think about them.
There've been some suggestions in other threads, but I'd like to discuss this over here, so this discussion doesn't get drowned in all those other topics
For this particular topic, I'd say we leave things open in the official books that we'll release, rather giving only hints, legends and opinions, which may all be contradictory. Let's leave the final decision to the individual DM himself.
Little idea to throw in: Some Hordlings (some Hordes?) might consider Night Hags (the race or certain individuals) to be "mommy" ...