Ian Jackson wrote
Rod Speed wrote
Ian Jackson wrote

I was alarmed to find that the 'mineshaft' was almost full to the brim
with fine sand - which presumably had been transported there by ants.

Unlikely.

So how did it get there?

Most likely the result of floods etc.

It certainly wasn't there when we moved here. BTW, the soil is essentially
heavy clay and flint - but when the ants make a nest in the lawns, the
create a small erupting 'volcano' of fine sand at the entrance hole.

Sure, but they don't fill holes with sand.

I have a couple of holes like that, one for the lawn sprinkler taps
and one for the solenoid valve that was my kludge that avoided
me doing anything about the leak in the copper plumbing under
the concrete slab and plenty of ants, but neither of those filled
with fine sand.