Specific metabolic heat rates (R_q) and respiration rates (R_CO2) of adult Harmonia axyridis Pallas, the multicolored Asian lady beetle, and Hippodamia convergens Guerrin-Manaville, the 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 were calculated as functions of temperature from the calorespirometric data. The two species have similar heat and CO₂ rates from 0 to 10°C, but both rates are higher for H. convergens at all other temperatures. Anabolic rates and R_q/R_CO2 ratios indicated high-temperature stress in H. convergens at 40°C and at 35 and 40°C in H. axyridis. Anabolic rates and R_q/R_CO2 ratios for the two species differed markedly from 15 to 30°C, where H. convergens had a higher anabolic rate and lower R_q/R_CO2 ratio (i.e., greater metabolic efficiency) than H. axyridis. The data show that H. axyridis maximizes the anabolic rate, and therefore the biosynthesis rate, at low temperatures around 5°C and maximizes the catabolic rate at 25–30°C to support movement. In H. convergens, the optimum temperature range is the same for both biosynthesis (anabolic rate) and movement (catabolic rate), i.e., from 15 to 30°C. The ability of H. axyridis to more efficiently use periods of low temperature for development and reproduction and periods of mid-range environmental temperatures for searching for prey and feeding probably contribute to its competitive displacement of native North American coccinellid species.