Why bees?

Bees appear to be one of the few creatures you can send through the post. the only restriction is that they be "enclosed in packs constructed so as to prevent injury to Parcelforce Worldwide staff, its agents or damage to other parcels".

So, if you write "bees enclosed" in big letters on the outside of the envelope it's fine.

Why bees as opposed to any other creature? Is there something important I'm missing about the bees?

I'm off to try and get a bee in an envelope.