The species of botfly we have here in the US are harmless to humans. Not so in other parts of the world!
Yep, just scrape the eggs off, or ignore them. The lifecycle requires the horse to scratch his legs with his teeth, thereby ingesting the eggs, which hatch in his gastrointestinal tract and bore through his gut. This, obviously, can cause some pretty serious problems...but most conventional dewormers kill the larvae, and you're never going to get all the eggs off, anyway, so as long as your deworming program is appropriate, your horse will be fine.