This fan has the characteristic ragged, chewed edges that indicate a borer infestation.

You can be absolutely sure that a borer has passed down through the fan by the frass (excrement) left behind in the fan. The borers (2) were only about half an inch long as this took place in late May, peak TB time in Maryland. Clarence Mahan had thoroughly squashed every borer in the clump--I went another two years before finding a good shot of an undamaged borer and that was only a small specimen.