I noticed a hole in the ground where the trees had been removed. Is the insect feeding off the roots that remain? Now I notice holes in the ground within 4-5 feet from an oak that is located about twenty feet from where the willows were. Ants also invaded the willows which speeded up their demise.
There is no buildup of dirt, etc. on the outside of the holes in the ground. The openings are "smooth".