If Fillydelphia is where juvenile mares are nurtured in da Keystone State, would their "equine-boy" counterparts come from locales such as Colt's Station or Camp Colt?
Someone or something that bites your ankles.
To a postman, an ankle biter is often known as a dog.
To an adult, an ankle biter may be a toddler.
To hikers, an ankle biter is sometimes a tick.
And so on.