These piles could be drywood termite droppings known as frass.
Termite frass termite droppings from ceiling.
The peculiarity of the drywood termite is frass fecal droppings of termites.
Unfortunately if frass is kicked out of a termite burrow in the ceiling or some other place it can fall unto the floor wooden or carpet where it is unlikely to ever be detected.
Piles of wings or mud tubes.
When they clean out their nest they push these droppings out through holes.
While cleaning their nests they push this frass outside of their nest through the holes.
When two drywood termites establish a small nest in wood they seal the hole they used to enter the wood and do not leave the nest.
This is especially true for homeowners who have know clue what frass looks like.
Termite droppings is the important sign of the presence of drywood termites.
Often these pellets look like coffee grounds however they can imitate the appearance of sand and sawdust as well.
When it comes to the color termite frass differs greatly depending on the kind of wood and cellulose food source ranging from dark brown to beige.
When drywood termites infest structural timbers in your ceiling cracks may occur due to the shifting wood.
Unlike sawdust which looks more like small shavings and slivers the frass consists of multicolored light white and dark brown granular pellets.
So there would be small black marks and dark substances which would result into the termite droppings.
If you look closer you may notice that a drywood termite pellet has six concave surfaces and rounded ends which makes it similar to a deflate football or an oblonged pea.
Termite droppings drywood termites leave behind ridged light brown fecal pellets called frass.
Mysterious piles of pellets are indicative of drywood termite presence.