Catalpa trees are flowering right now. They have big heart shaped leaves and pretty white flowers. They produce long slender bean pods that hang down. Birds like the tree for the dense cover.
I really have never noticed the bees working the flowers much. The significance of the flowering Catalpa tree is that it is the same time as the Basswood/ Linden tree nectar flow. It is easy to spot the trees from a distance to help give a clue when Basswood nectar is coming in.