To test many predictions of "optimal foraging theory" it is necessary to calculate the rate of net energy intake of a foraging animal. Equations are derived for the calculation of the rate of net energy intake of a foraging bumblebee. The assumptions that form the basis of these energy equations are discussed. As examples, the rates of net energy intake are calculated for Bombus flavifrons workers foraging on neighboring patches of Aconitum columbianum and Delphinium barbeyi. If the bumblebees forage optimally, their net rates of energy intake in the two patches should be equal. The observed rates are consistent with this hypothesis. The application of an optimality approach to pollination biology is briefly discussed.