Dear Land-Sheller’s

While I was looking after land shells, I “discovered” that there are
Plenty of empty shells in the grit of seeds around Ants nest.
Most of them are of the kind of Euchondrus septemdentatus, which looks very
much like a wheat grain by itself.
Now my question is – why?
Were they collected by the ants as ‘seeds’ and than disappointedly removed?
Or were they collected as nutrition for the ants?
Or maybe dug out by the ants while digging their nest?
Are you familiar with these phenomena?
Please shed some light ;-)
Regards - uri