This snake story was still quite fun and I would be very much up for it being expanded upon. I just realized that the snakes leaving once they reach adulthood also means they should simultaneously be of breeding age. There could be an explanation of why they need to devour the young girl at this stage as the girl's meat and hormones help kick start the snakes breeding cycle, since the girls are also going through puberty at this time. It can be portrayed as an honorable sacrifice and a pleasurable experience and unique to the girls as Adult women do not have the same hormones and so can't provide the snakes the same level of nourishment.

Oh, perhaps 2 snakes who had recently devoured girls other than their hosts, are ready to breed so the girls have to use them as living strapons. Or perhaps the snakes coil around their legs to control their walk to lead them to potential mates.

Perhaps the snakes don't really need to eat the entire girl and one just devours her ovaries and decides to mate with his host instead. Nesting in her womb and fucking her ass and mouth when horny and emerging to suckle on her breasts when hungry.

Dunno, just spitballing ideas for you. =P. And hope to see more of your stories!