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These larvae were found under a now abandoned hornet (Vespa crabro) nest (NW Slovenia). They were residing under a PVC cover (the dark patch seen on the floor) which was uncovered for the purpose of this image. Some larvae have already traveled some distance and pupated (dark ones).

Any tips on what dipteran larvae this may be? Phorid maybe? Is this species/group known to be associated with hornets? I'm curious how they came to be there and why they stayed. Maybe something was oozing/falling from the nest serving as nutrition? I don't think it's likely that they fell out of the nest.

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Not Phoridae - perhaps Achanthiptera rohrelliformis (Muscidae)?

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Thanks Tony. If this indeed is A. rohrelliformis, how do you reckon they came to the floor? Could all those larvae have fallen out of the nest? Or maybe something drove them out? Have you encountered any literature on this subject by any chance?

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Having read a bit more about Achanthiptera, I think the puparia are too dark for this species - but there are many other flies that inhabit hornet nests. If you have a sample of larvae and puparia, then examination of the mouthparts and spiracles should enable a family determination.
Often larvae will leave their food source to find somewhere to pupariate, but the density of these larvae suggests that there may have been a food source under the PVC.

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Thank you for your efforts. Unfortunately I don't have the pupae or larvae handy so we'll have to leave it at that. But an educated guess that these larvae may have come from the nest and somehow migrated down may be good enough for now.