Most aspects of the bumblebees' rule of departure from an inflorescence of Aconitum columbianum are qualitatively what would be expected if the bumblebees maximize their net rate of energy gain. Flower revisitation increases with increases in the number of flowers already probed on an inflorescence and with decreases in the number of flowers available. Nectar volume per flower tends to decrease with increasing relative flower height and there is a positive correlation between nectar volumes of flowers from the same inflorescence. Consequently the bumblebees should be increasingly likely to leave an inflorescence with increases in either the number of flowers already probed or the relative height of the last flower and with decreases in either the number of flowers available or the nectar volume obtained at the last flower. The bumblebees showed all these trends.