To ask if anyone knows what this might be (probably pest related)

[5foot5]

See image.

There is a hole in the corner of a wooden window sill and there are little black things around it

Anyone?

Is the wood rotten? If so I'd get you've got some kind of infestation and the black bits are droppings. Good luck!

Maybe mouse droppings

Pretty sure not a mouse. I know what mouse droppings look like and these are much smaller.

I am guessing some sort of infestation but wondered if anyone knew what it might be so we can deal with it. It is an indoors window sill and house only just over 20 years old

Where does the hole go? Does it lead outside or is it just a crater type thing in the sill?

I would have also guessed mouse based on the hole just appearing. Leave a mouse trap beside it and you'll soon know.

If the window sill is rotten which it looks like it is, can you not take the whole sill off and see what the infestation is and then replace with a new piece of wood.

Probably not an expensive job for a carpenter to do.

From having a rotten window myself I would suggest woodlice, surprising in a 20 yr old house though!

I mean the droppings, not what would have made the hole!

Are they actually droppings? They look very square ended to me.
If you put them on a damp bit of tissue do they dissolve/stain the paper? Just wondering if they could be little bits of the wood?

Are they mushrooms in the hole?!

Cockroaches?

Sadly OP, it looks to me as though it is either Dry Rot or Wet Rot, both of which are caused by fungal infections. The speckles everywhere don't look like droppings to me - they almost resemble vermiculite, which is used as an insulating material, amongst other things, though usually as an 'infill' in chimneys which have a metal flue liner

They don’t look like droppings…. Not sure what would be tho