I never seen one and neither has my husband, never had them on us. It freaks me out. So it could have been on him for who knows how long but not have started to eat off him i guess till wed night - thursday morning because according to the vet it takes up to 24 hrs to get to a size of a pea then will fall off easy when the are done.
I joined a beagle club so that was new, I know i will never figure out where it came from. I will have to make it a habit to check him.