What is this domestic freakery (includes images, possibly of small dead things)

[Nowdecide]

This debris is on our bedroom window sill. I clear it away, more arrives, within a day.

I suspect ants. Maybe down between the sill and bit at the back?

Can anyone identify it and/or suggest a remedy?

I've never seen the like.

[justdontevenfuckingstart]

We had this, I think it was shell casings (?) from some sort of insect. We siliconed up the brickwork from the corner of the windowsill it was piling up in.

[Nowdecide]

Ah, thank you justdontevenfuckingstart (nice, if scary name, btw, respect) so you think they come from outside? Hmmm. Interesting.

[justdontevenfuckingstart]

Had it at work too, came through the brickwork. Never actually saw any creepies.

[Nowdecide]

Bit odd as the garden is outside - and the ground is level with the bottom of the window. So no wall beneath window (there is but it's earth under the garden against wall if you see what I mean) so no exposed brickwork externally.
Could they be inside the wall?!

[Nowdecide]

Carpenter ants! Found more detail based on your replies. Looks like we have an infestation. . .

[justdontevenfuckingstart]

Yes the debris we had was exactly the same when I googled.