Recent studies demonstrate that Harmonia axyridis Pallas is displacing native coccinellids in North America. Although we do not completely comprehend why this phenomenon happens, understanding of respiration and metabolic activities should help clarify mechanisms of interspecific competition. In this study, the metabolism and physiological ecology of H. axyridis is compared with that of Hippodamia convergens Guerrin-Manaville using calorespirometry. Metabolic heat rates (R_q) and respiration rates (R_CO2) of adult multicolored Asian lady beetle, and convergent lady beetle were measured in isothermal calorimeters at 5°C intervals from 0 to 40°C. Anabolic rates and R_q/R_CO2 ratios which are indicative of energy use efficiencies were calculated as functions of temperature from the calorespirometric data. The results show H. convergens has a higher anabolic rate in the mid-range of temperatures from 15 to 30°C and tolerates higher temperatures better than H. axyridis. Although the two species have similar metabolic rates and efficiencies at temperatures from 0 to 10°C, H. axyridis tolerates temperatures below 10°C better than the H. convergens. These data agree with field observations in the temperature range of 15 to 30°C.