I don't want to be pedantic but if you are talking about an individual bee and comparing sizes of things to his dick then its 'half a bee's dick' as the dick belongs to that particular bee.
But if you are creating a standard unit then the unit is '1 bee dick' singular and if you are measuring things against that standard unit you will need a range that assumes more than one unit so your graduation should be labelled 'bee dicks' as in 10 bee dicks for example. That was my thinking anyway, I may be wrong grammar is not my strong point.