Hi Kriszta

The short answer is that I have absolutely no idea. However, I have often wondered about this. There seems to be no consistent theme but I do notice that bright, pale blue or green eyes is often a feature of small, fast-flying summer bees such as the subgenus Heliophila of Anthophora. This includes bimaculata as you point out. Another is Megachile leachella - a small, fast-flying summer megachilid. On the continent other genera like Tetraloniella or Anthidium have pale-eyed forms. Again, it seems to be smaller, summer species that do this. Maybe the pale eyes are of assistance in rapid, highly-manoeuvrable flight - perhaps helping to reflect more light onto the back of the facets. The only problem with my theory is that there seems to be as many exceptions as there are species that follow the rule! But, as I say, this is only speculation. I would love to know if anyone else has any ideas.

Ian