I would guess that some sort of 'critter' got into that piece of fabric and left you a present! I've had it happen when field mice came in (through the dryer vent??) and decided that my linen drawer was a perfect nesting spot. Not only did they leave a mess and damage some of my tablecloths, they brought in the little mites as well.
I washed everything in hot water and the whites in bleach, then dried on the highest setting on my dryer. Took care of it, except for the holes in my crocheted tablecloth. Haven't repaired them yet, and its looking like I may not since it has been several years already. LOL!
Hot water, bleach and a hot dryer should take care of your problem.