IF I WERE inventing a fairy tale, one of the characters would be a leaf-cutter bee. He would be one of the good guys. All week I have been watching these perky insects visiting the borage under our window. Picture a slender version of the honeybee, and add a bright orange abdomen. In the shadows cast by our dense, blue flowers, the leaf-cutters look like searching torch beams. Not only strikingly coloured, as they fly their abdomens lift slightly as though offering a saddle to ride upon. In any fairy tale worth its salt, there would have to be an escape on the back of a friendly leaf-cutter. Naturally, with the falling of night, the abdomen would light the way. Remarkably, the reality is hardly less amazing. Take their nest building. These bees select a leafy plant (in our garden, pumpkin