What did this - sand on floor

I got a call from a client today that says this there has been sand on the floor (more and more, I think) for the past few years since he bought this house. Its a small room (wine cellar) in the basement of the home. Block wall, dirt floor with 1x4s laid down. The floor is about 7 feet below grade. He called today because now there are dirt mounds outside, but that is just a coincidental pocket gopher, which I wouldn't think is the cause of this sand. I suggested maybe ants, but he says he has never seen ants down there. What do you guys think did this?

My initial thoughts were ants as well. If the sand can be inspected, if it's ants the sand will be dirty with insect parts and other debris.

I’ll be curious to hear what others say about this as well.
If there are critters involved, I would think it must be insects. I’d be down on my hands and knees trying to find any larval casings, droppings, body parts, etc.
I see what appears to be rings of sand, which look like aging anthills. The one in the bottom left(ish) corner looks like an anthill that has collapsed back down through the crack.
If the customer is patient, then perhaps sweep the floor to drive the sand back down between the cracks, then wait and see what reappears.

I'd guess ants too.

I would guess some kind of insect, I would clean up the sand and put down some glue pads. JMO

Webfootwhacker- Have you physically inspected the site to determine that the substance is, in fact, sand? To me, it looks like it could be frass from wood destroying insects or larva. I have seen frass resulting from carpenter ants, termites, carpenter bees and wood boring grubs.

If indeed sand, I'm thinking a hydraulic effect from water bringing up sand and it settles on the boards, then runs back thru the cracks.

Thanks for the replies guys. I will keep all of this in mind when I do the inspection on Tuesday and report back.

I know I'm from the South but that sure looks like termites or carpenter ants. We see that year round down here. We don't have basements but I would think it would almost have to be an insect to be 7' below grade. I doubt it's water as there is no staining and it looks loose.

Sarlacc sand creature, an invasive species from the desert planet Tatooine specifically found in Great Pit of Carkoon.
Whatever you do, don't fall in!

I’m no bug guy, but after consulting with a reputable one in my area, he says carpenter ants. I got some better pics for him and he was pretty confident. To answer LA trapper’s question, it was a mix of larval casings insect parts and sand. Referred the bug job and doing the gopher myself - win win.