Fig. 1. Elevated thoracic temperatures of foragers feeding on sucrose solutions. The relationship between thorax temperature (T_th) and ambient air temperature (T_a) for feeding bees. With the exception of seven measurements from evidently ectothermic foragers at the lowest sucrose concentration (marked by black arrows), all T_th values are above T_a (lower broken line). Pooled data from all colonies for the highest and lowest sucrose concentrations (m) used are shown (m=0.5 mol l^-1: N_colonies=6, N_measurements=250, N_{individual bees}=161; m=2.5 mol l^-1; N_colonies=6, N_measurements=497, N_{individual bees}=161). Linear regression lines with y-intercept values are given.