Lasius Niger fungus garden?

[jarnozoxx]

Hi,

I've had this Lasius Niger colony for about 2 years and I have noticed something weird.
In one of the chambers of the nest (Ytong nest) they're constantly busy with what I would imagine a fungus garden would look like. This seems unlikely to me because Lasius N. doesn't usually have them. I thought it could be a garbage pile, but why would they tend to it and keep some larvae close?

Pictures:



Does anyone have any idea what it could be?

Thanks!

[Batspiderfish]

Most cocoon-using ants bury their mature larvae before pupation, to provide anchoring points for the silk.