The people who wrote the books being too oblivious to realize the monsters were having sex seems to be a thing (that, or in the closet and not mentioning it), but if it doesn't mention where to find something, you can typically get it from sex.
Basically Flint is the first one to ever tried fucking the monsters. The others were too scared to push their studies far enough to give proper answers. Hence why they never really met the lamias or even visited the ghost sea.
