Probably baby ticks. I get them on my pants and they look like a spot the size of a quarter...then the spot starts to move...it's hundreds, maybe thousands, of ticks. They quickly spread out and are very hard to get off your clothes, and skin if they get to it. The best way to get them off is wrap duct tape around your hand with the sticky side out and roll the adhesive side all over your clothing, they will stick to it.