Not A Clue...!!??

As to what’s causing these....they are appearing all around our garden wood now..and we have no idea who is doing it....yesterday we did see some wasps flying around and actually coming out of some of the holes and sawdust...!
Hubby has swept some of it up but whoever they are...they are extremely industrious and the large piles of sawdust appear very quickly again...
The wood is around the garden about 10 years now and is probably getting to the soft rotting stage..
Has anyone any ideas or advice we would greatly appreciate it...!!???