Bees and Spuds

I was surprised last week to find a bee when turning out some spuds, I thought it was maybe been sat on a leaf, or landed nearby for a closer inspection, but today found another two that I can only assume were buried (yep, buried!) in the soil. Four questions: Anyone know what these are, what they were doing (I think nesting?), why they only like spuds (to date) and if I can (or indeed want to?!) tempt them back?

Ta!! Bzzzzzzzzzzzzzz.......