[arm85]

Some hives have enclosed floors. But modern hives, at least in the UK, now have a mesh floor. Which is there to reduce the numbers of a parasite, varroa. The mesh allows the parasite to fall out of the hive.

[DFHippie]

It's been a couple years since I kept bees, but it's the same in the US: a mesh floor the better to shed the mites.