I have kept, bred, caught wild snakes and "Milked" snakes in my days. Bee larvae are rich in nutrients, a fact any wild animal would take notice. Snakes tongues are used for smelling and in some varities, assist w/ heat detection. Like some one else pointed out, animals often do that which is unrecognized in books. They don't read after all. I wouldn't worry about a snake eating some larvae. Snakes don't consume huge amounts of food like a skunk for example. A few larvae would probably suffice to fill a small snake. I like snakes, so I wouldn't do anything. Also, top entrances would probably work, but an opening big enough for the bees is probably big enough for some snakes-no matter where the entrance is placed. Snakes have no shoulders, and can get into places most animals could never get into. Picture please so identity could be ascertained.