Tarantula. Thermogram of a tarantula held by a pair of hands. A thermogram shows variation in temperature on the surface of an object, measured by the long-wave radiation it emits. The temperature scale is colour-coded and runs from dark blue (coolest, 22.8 degrees Celsius) through green, yellow and orange to light red (warmest, 35.9 degrees Celsius). The tarantula is cooler than the human because it is an ectotherm. Ectotherms use their external environment to regulate their body temperature while endotherms (mammals and birds) are able to regulate their body temperature internally.